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Link Between Eating Meat and Cancer Risk Varies by Race

Link Between Eating Meat and Cancer Risk Varies by Race

Scientists find link between meat and breast cancer depends on race

Wikimedia/Carl-Magnus Helgegren

While studies have indicated that eating a lot of red meat can have a negative effect on a person’s health—including increasing risk of death from cancer—and the American Cancer Society recommends eating red meat only two or three times a week, new research shows that the effect of meat consumption on cancer risks actually varies depending on a person's race.

According to HealthDay, a new study found from the Cancer Institute of New Jersey found meat consumption was linked to an increased risk of breast cancer in white women, but the scientists found no such correlation between meat consumption and breast cancer risk in black women.

"Most breast cancer studies have been conducted in [white] women," said researcher Elisa Bandera in a press release. "Our study provides new information on the role consumption of animal foods play on breast cancer development in women of European and African ancestry."

The study actually suggests that eating relatively large amounts of red meat may even be associated with a reduced risk of certain kinds of tumor in black women. But the scientists say more research is necessary before the findings can be considered conclusive.

“This research supports encouraging Caucasian women to limit their intake of both red meat and poultry in order to reduce their risk of breast cancer,” wrote researcher Urmila Chandran. “Being that this study may be one of the first to examine this association in African-American women, results from this group are not conclusive, and more investigation is needed to replicate these findings.”


Red meat and the risk of bowel cancer - Eat well

Red meat – such as beef, lamb and pork – is a good source of protein, vitamins and minerals, and can form part of a balanced diet. But eating a lot of red and processed meat increases your risk of bowel (colorectal) cancer.

That's why it's recommended that people who eat more than 90g (cooked weight) of red and processed meat a day cut down to 70g or less. This could help reduce your risk of bowel cancer.

Other healthier lifestyle choices, such as maintaining a healthy weight, keeping active and not smoking can also reduce your risk.


Types of Vegetarians

Although all vegetarians avoid eating meat, poultry and sometimes fish, there are many different variations of the vegetarian diet.

    who do not eat any animal products such meat, poultry and fish, including dairy products, eggs and honey.
  • Lacto vegetarians avoid all meat, poultry, fish and eggs, but they consume dairy products.
  • Lacto-ovo vegetarians don't eat the flesh of any animal. No meat, poultry or fish, but eggs and dairy products are acceptable.
  • Ovo vegetarians eat eggs but refrain from eating meat, poultry, fish and dairy products.
  • Pesco vegetarians or pescatarians avoid meat but may eat fish.
  • Pollo-vegetarians don't eat red meat but eat poultry.

Seeing red

Scientists have offered a number of explanations for the link between red meat and colon cancer. One theory blames heterocyclic amines (HCAs), chemicals produced when meat is cooked at high temperatures. HCAs may play a role, but since high levels can also be present in cooked chicken, they are unlikely to be the whole explanation. Preservatives have also been implicated in the case of processed meats nitrates are a particular worry, since the body converts them to nitrosamines, which are carcinogenic. But since fresh meat is also linked to colon cancer, preservatives can't be the whole answer.

Scientists from England have offered a new explanation. Their investigation recruited healthy volunteers who agreed to stay in a metabolic research unit where their diet could be carefully controlled and all of their fecal waste could be collected and analyzed. The volunteers ate one of three test diets for a period of 15 to 21 days. The first diet contained about 14 ounces of red meat a day, always prepared to minimize HCA formation. The second diet was strictly vegetarian, and the third contained large amounts of both red meat and dietary fiber.

Stool specimens from the 21 volunteers who consumed the high-meat diet contained high levels of N-nitroso compounds (NOCs), which are potentially cancer-causing chemicals. The 12 volunteers who ate vegetarian food excreted low levels of NOCs, and the 13 who ate meat and high-fiber diets produced intermediate amounts.

These results are interesting enough on their own, but Dr. Michelle Lewin and her colleagues went one step further. They were able to retrieve cells from the lining of the colon that are shed into the stool with every bowel movement as a normal event. The cells from people eating the high-meat diet contained a large number of cells that had NOC-induced DNA changes the stools of vegetarians had the lowest number of cells with damaged genetic material, and the people who ate high-meat, high-fiber diets produced intermediate numbers of damaged cells.

Did you ever wonder what puts the red into red meat? The short answer is myoglobin, a protein that looks red when it binds with oxygen. But after a few days in the refrigerator, myoglobin gives up its oxygen and the meat turns brown. To keep meat looking rosy, manufacturers may pump in some carbon monoxide, which sticks to myoglobin like glue, keeping it red for weeks. Carbon monoxide is also used to keep tuna looking fresh, and a variety of additives are used to improve the appearance of other foods. The moral: Don't judge a food by its color.


Animal Protein and Cancer Risk

Claim: A plant-based diet with minimal to no animal protein is the best diet to lower cancer risk.

In this article we will be reviewing various animal proteins and if the consumption of these foods is associated with an increased risk for cancer. We will also explore the effects of preparation and processing of the animal protein compared to the protein itself. Our goal is to evaluate and decide whether or not it is safe to eat an omnivorous diet and to discuss specific guidelines as to how much, how often, and with what overall dietary pattern we should be aiming for.

There have been several decades of research on this topic. We have limited our review to the last 10 years to try and get the most recent data on this subject. We will spend quite a bit of the discussion looking at the mechanisms as to why some animal proteins may be more problematic than plant sources of protein.

Below is a list of the animal proteins we will be researching.

Animal Protein

Red meat that has been preserved (curing, smoking, salting, drying)

Cooking and Processing Methods

Cooking animal foods at high-heat will create carcinogens. The by-products include Heterocyclic Amines (HCAs) and Polycylic Aromatic Hydrocarbons (PAHs). HCAs are made when creatines and amino acids (both found in meats) react together with heat. This reaction starts to occur at 212 F (100 C) but happens more rapidly from about 572 F (300 C) and higher. PAHs include over 100 different compounds formed by the incomplete burning of organic matter at temperatures in excess of 392 F (200 C). Essentially the hotter and longer a meat is cooked, the more HCAs and PAHs produced. Direct heat methods like grilling and frying produce more HCA’s and PAH’s than indirect-heat methods like stewing, steaming, or poaching.

Processing meats add chemicals, like nitrites, that generate N-Nitroso Compounds (NOCs) another class of carcinogenic compounds.

Does the problem lie with the nutrients within the animal food? Some of the problems that will be discussed further relate to the fat content, specifically cholesterol content of the food. Another concern is heme iron, which is particularly high in red meat, liver, and processed meat. Yet another concern lies with choline content, which is high in eggs, liver, red meat, and milk. The potential concern with choline is that it is eventually converted in the liver to trimethylamine oxide, which increases inflammation in the body. (1)

Yet another potential problem is how the industrialized husbandry practices affect the quality of the animal food we are eating. Pesticides used on feed and/or medications or hormones given to the animal can create toxic residues left in the meat that we then consume. In addition to whether pesticides are being used on the feed, what the animal is eating is equally important. As discussed in Important Foods for Cancer Patients, there is concern regarding the inflammation producing properties found in meat from animals fed grain-based diets. According to a Review written in Nutrition Journal in 2010 (2), grass-based diets produce higher contents of omega-3s and CLA in the beef as well as higher levels of antioxidants. We’ve discussed the anti-inflammatory benefits of Omega-3s throughout the website. Conjugated Linoleic Acid (CLA) is a naturally occurring fatty acid made from the omega-6 essential fatty acids found in meat and dairy. The isomers of CLA have been studied for their potential benefit with immune support and in weight loss. Research suggests that pastured cows produce up to 500% more CLA than grain-fed cows (2).

What is the Evidence?

Before we get into the details of the research we reviewed we think it’s important to point out some of the limitations of the research in this area. Almost all of the studies we reviewed were pre-clinical animal model studies, which means that those results may or may not translate to human populations. Most of the rest of the studies were epidemiological, which is not possible to be conclusive regarding cause and effect. It’s also important to point out that none of the studies commented on whether the animal protein consumed was organic or grass-fed. Based on what we know about the inflammatory markers alone this is a very important factor when making correlations between exposure and disease risk.

In the text above we described how cooking methods are one of the factors contributing to the concern with meat and cancer. The by-products of high heat cooking have been shown to be carcinogenic. According to a number of pre-clinical animal studies, HCAs have been shown to increase the occurrence of tumors in multiple sites mammary, lung, colon, stomach, prostate, pancreas, esophagus (3). It’s important to keep in mind that any animal protein can create HCAs if cooked at a high enough heat.

Although the studies we reviewed showed a positive association with high meat intake and the following cancers: esophageal, lung, pancreatic, colorectal, breast, and stomach, there were mixed results seen for a correlation between meat intake and endometrial, bladder, or ovarian cancer.

Among over 60,000 women in the Swedish Mammography Cohort, a modest elevation in risk for endometrial cancer was shown with those with the highest intake of heme iron, especially from consuming liver (4). There was no statistically significant association observed for intakes of other red or processed meats. The pooled results of 10 cohort studies and 11 case-control studies indicate that overall meat intake was not related to risk of bladder cancer, however, those with the highest intake of red and processed meats were at a 17% or 10% increased risk respectively (5). A dose-response meta-analysis of 8 cohort studies concluded that there was no association seen between the intake of red and processed meats and the risk for ovarian cancer (6).

According to the results of 4 different meta-analysis (7-10), the combined results of 7 cohort and over 30 case control studies, concluded that individuals with the highest intake of red meat, which was measured at 3.5-4.2 ounces of red meat per day, have an increased risk for developing esophageal cancer ranging from 26-57% higher risk depending on the study. Most concern seems to lie in the high amount of heme iron found in meat as well as the HCAs and PAHs produced from cooking meat at high temperatures.

A number of studies in the literature have examined the association between red meat intake and colorectal cancer. The potential mechanisms may be due to the production of HCAs secondary to high-heat cooking. According to 1 meta-analysis of 16 case-control and 5 cohort studies, for every 100 gram (3.5 oz) per day increase in red meat intake there is a 36% increased risk of colorectal cancer (11). According to another meta-analysis of 3 case-control and 21 cohort studies, the risk of colorectal cancers significantly increases linearly with increasing intake of red meat up to 140 grams (5 oz) per day, where the curve approaches its plateau (12).

For breast cancer the association between red meat intake and increased risk seems to be due to a combination of factors including heme iron content, by-products of cooking, exogenous hormones used to treat commercially raised cattle, and an animal sugar known as NEUR5gc, which can be absorbed by human tissue and leads to inflammation and tumor formation in prospective studies (13). One prospective study suggested an association between higher red meat intake in early adulthood and increased risk for breast cancer later in life (14). This same study showed that by replacing red meat with a combination of other proteins (legumes, poultry, nuts, fish) one could reduce their risk for breast cancer.

The heme iron content of red meat may also be implicated for an increased risk of stomach cancer as heme iron is a growth factor for H. Pylori (15). The by-products of high-heat cooking have shown an association with an increased risk of pancreatic cancer (16). Reviewing data from a large prospective cohort study (over 12,000 people) showed that total dietary fat intake, specifically saturated fat from red meat and dairy products, was associated with increased risk for pancreatic cancer (17). Furthermore, a meta-analysis of pancreatic cancer risk factors showed a positive association with red meat consumption, but only in men (18). Consuming meat 3 or more times per week may also increase the risk of lung cancer by as much as 35%, according to evidence from the meta-analysis of 23 case-control and 11 cohort studies (19).

Processed Meat:

The link between cancer risk and consumption of processed meats is well supported in the literature. This association is due not only to the mechanistic concerns with red meat, heme iron content, HCAs and PAHs, but also from the processing methods that add an additional layer of toxic compounds.

As with red meat, the association with processed meat and esophageal cancer is relatively robust. A 2014 meta-analysis showed high processed meat intake was likely to increase the risk of esophageal cancer (10). Two other meta-analysis showed associations that individuals with the highest consumption of processed meat, measured between 50-100 grams per day (1.75-3.5 oz), were at highest risk for developing esophageal cancer up to a 40% higher risk (7, 9). In other observational studies, the risk ranged from 41-55% of developing esophageal cancer for those with a high intake of processed meat (8, 20). With many of these studies, the primary concern relates to the heme iron content. Salted meat consumption in particular seems to have a strong association with esophageal cancer, particularly when it’s combined with alcohol and/or smoking (21).

Salted meat also seems to increase the risk of gastric cancer, according to another meta-analysis (22). The high salt intake damages mucosa within the stomach and increases the risk for H. pylori infection a known risk factor for gastric cancer.

As was the case with red meat, the consumption of processed meat poses a significant risk for colorectal cancers. According to meta-analysis, processed meat intake is even more closely linked with colorectal cancers than intake of fresh red meat (23). For every 50 gram (1.75 oz) per day increase in processed meat intake there is a 28% increased risk of colorectal cancer (11). The risk of colorectal cancers significantly increases linearly with every 50 gram per day intake of processed meat up to 140 grams (5 oz) per day, where the curve approaches its plateau (12).

As with that of red meat, the association between processed meat intake and increased risk of breast cancer seems to be due to a combination of factors including heme iron content, the by-products of cooking, exogenous hormones used to treat commercially raised cattle, and an animal sugar known as NEUR5gc, which can be absorbed by human tissue and leads to inflammation and tumor formation (13). Furthermore, smoked meat seems to be a particular problem. In a case-controlled study of 400 women, daily intake of smoked meat significantly increased risk for breast cancer in both pre and post-menopausal women (24).

The by-products of processing have also shown associations with several other cancers. There is an increased risk of oral cancer with increasing processed meat intake (25). N-nitroso compounds (NOCs) also seem to be particularly problematic as they have been shown to reach the pancreas via the blood stream. They are potent carcinogens in pre-clinical animal studies thereby increasing the risk for pancreatic cancer (18). They have also been shown to cross the blood brain barrier, which may increase risk for glioma (26).

Poultry, on the other hand, may lead to a decreased risk of cancer. A meta-analysis looking at poultry intake and colorectal cancer showed a significant inverse association with at least a 50 gram (1.75 oz) per day poultry intake (27). The incidence of esophageal cancer and lung cancer were also decreased with poultry intake (10, 19). The mechanisms responsible for this inverse association may be explained by an overall healthier lifestyle or because of the lower heme iron content in poultry. There was one study looking at the post-diagnosis diet of over 27,000 men diagnosed with prostate cancer which found an increased risk of cancer from those eating chicken with the skin on (28). This increased risk is likely secondary to the formations of HCAs and PAHs from high-heat cooking.

Dairy is an interesting category of animal food as it seems to show some negative and some positive associations with risk for cancer. Certain components of dairy foods such as probiotic content, calcium, vitamin D, and CLA may all have protective effects. Where-as other compounds such as IGF-1 and phosphorous may have negative effects.

The research is mixed around gastric cancer. A 2015 meta-analysis of 17 case-control and 6 cohort studies showed protective effects with the highest total dairy intake and hypothesized that it may be due to the anti-cancer properties of vitamin D and calcium or probiotic-rich dairy foods (like yogurt and kefir), which interfere with H. pylori colonization, or even the phospholipid content increasing cellular renewal (29). Another meta-analysis showed that dairy products were unlikely to be strongly protective against gastric cancer but didn’t increase risk (30). And yet another meta-analysis showed a non-significant increased risk of gastric cancer with dairy intake (31). As you can see, the research is somewhat conflicting.

The CLA in dairy may be protective against breast cancer due to its anti-inflammatory properties (32). The authors hypothesize that calcium and vitamin D may also offer anti-carcinogenic benefits on breast cancer cells. A meta-analysis of colorectal cancer showed a statistically significant reduction in risk with high intake of milk (7 oz per day) and total dairy, excluding cheese (14 oz per day) (33). The authors hypothesize that the protection is likely due to high calcium intake as trials have found reduced risk of colorectal recurrence with calcium supplementation (1200-2000 mg/day).

There was no association between dairy intake and pancreatic cancer risk observed in a pooled analysis of 14 cohort studies (34). Although as mentioned above under “Red Meats”, the dietary fat content of dairy foods has shown some association of increased risk for pancreatic cancer (17). The results of a meta-analysis showed increased prostate cancer risk with high intake of dairy foods 14 oz/day total dairy, 7 oz/day milk, 3.5 oz/day yogurt, 1.75 oz cheese. One set of authors hypothesize that this is because of dairy’s IGF-1 content, which promotes proliferation of cancer cells and inhibits apoptosis of prostate cells (35). They also speculate that it could be due to dairy’s high calcium intake interfering with vitamin D levels. However, another set of authors believe that it’s dairy’s high phosphate content, rather than the calcium content, that reduces systemic serum vitamin D levels (36). Results from epidemiological studies examining the association between the use of dairy products and risk for ovarian cancer have been conflicting. According to one study, evaluating data from a large Danish population-based case-control study (with over 2000 women), an association between intake of dairy foods and increased risk of ovarian cancer was noted (37). The association, however, was strongest with milk and lowest for cheese.

Although eggs are lumped into an overall healthier dietary pattern in some prospective studies (chicken, eggs, legumes, nuts), there are other studies suggesting concern around egg consumption and increased cancer risk. For prostate cancer in particular, there are several studies which found an increased risk. According to a prospective study published in Cancer Prevention Research, healthy men who consumed 2.5 or more eggs per week had an 81% increased risk of lethal prostate cancer compared with men who consumed less than 0.5 eggs per week (28). The authors hypothesized that this was due to a high level of cholesterol and choline in the eggs, which are both highly concentrated in prostate cancer cells. In 2012, the authors looked specifically at choline content and found that men in the highest quintile of choline intake (471 mg/day) had a 70% increased risk of lethal prostate cancer (38). Although choline is found in all animal foods it is more highly concentrated in eggs at 250 mg per egg.

A meta-analysis published in 2015 showed a modestly elevated risk for not only prostate cancer but also breast and ovarian cancers for those with the highest intake of eggs, more than 5 per week, as compared to those with no egg consumption at all (39). These authors also suggest that the choline and cholesterol were causative. Choline may increase the proliferation and progression of prostate cancer (1), while cholesterol serves as a pre-cursor for the biosynthesis of sex hormones and a primary metabolite of cholesterol acts as an estrogen receptor agonist in breast cancer cells (39). Another 2015 meta-analysis showed an association between egg consumption and increased risk for ovarian cancer (40). Cohort studies have also shown an association between egg consumption and increased breast cancer risk especially for post-menopausal women (41). This seemed to be true for those consuming 2-5 eggs/week.

A 2014 meta-analysis published findings from 37 case-control studies and 7 cohort studies supporting the association between egg consumption and increased risk for GI cancers with a stronger correlation for colon cancer and in Western populations (42). Another recent case control study showed a connection between dietary cholesterol intake and risk of bladder cancer (43). Cholesterol is converted in the liver to primary bile acids, which are then converted in the gut by bacterial flora into secondary bile acids. The concern is that these bile acids produce reactive oxygen species, NF-kB activation, DNA damage, and increase cellular resistance to apoptosis (44). The overall risk for bladder cancer increased two-fold with an intake of 6 fried eggs per week versus those who ate 0 eggs. No association was found with boiled eggs, begging the question that the culprit may again lie with the by-products of high-heat cooking rather than the eggs themselves (43).

Fish on the other hand seems protective against cancer. The only exception might be fried fish. Frying fish decreases the omega-3 content of the fish and generates HCAs, oxidized lipids, and trans-fatty acids, all of which then increase cancer risk. A case control study found that frying fish increased the risk for pancreatic cancer (16).

Higher consumption of fish has been associated with decreased risks for all of the following cancers: esophageal, breast, ovarian, colorectal, and liver. The primary mechanism is thought to be related to omega-3 intake. Omega-3s inhibit eicosanoid release, which reduces inflammation. Omega-3s can also regulate transcription factor activity, regulate gene expression and signal transduction for cell growth, apoptosis, angiogenesis, and metastasis (45). Pre-clinical animal studies have shown that supplemental omega-3 has the ability to slow the growth of various cancers and fish consumption has been advised to reduce cancer occurrence (46).

A meta-analysis showed that a daily increase of 50 grams (1.75 oz) per day of fish lowers the risk of esophageal cancer (9). Another meta-analysis also showed an association between fish intake and lowered risk for esophageal cancer (8).

A meta-analysis of prospective cohort studies supported a higher consumption of fish (dietary marine omega-3) to decrease the risk of breast cancer 45. A 50% decreased risk was observed for every 1 gram per day intake of marine omega-3. However, no significant association was seen with plant based dietary omega-3. The fattier the fish the higher amount of omega-3 it contains. This association was demonstrated in a meta-analysis, which initially found no association between fish intake and risk for ovarian cancer but did find a significant decrease in risk associated with fatty fish intake (47).

Another meta-analysis found an association between fish consumption and prevention of colorectal cancer (48). Another study also showed that eating fish reduced the prevalence of colorectal cancers, which the authors felt was due to the high selenium content found in fish (49).

The anti-inflammatory properties of omega-3s were also found to be beneficial in reducing the risk of liver cancer (50). Liver cancer risk was reduced by 6-18% with a 1-2 servings per week intake of fish respectively (51).

What Is Our Recommendation?

The over-arching claim to avoid all meat and animal products is not warranted. You do not need to be vegan to lower your risk for cancer but you do need to consume a lot of plant foods. After reviewing recent research the risk versus benefit of animal foods varies quite a bit depending on the type of animal protein and the way it is prepared. Overall the cooking method (e.g., high temperature cooking) and processing of meat (e.g., smoking and curing) provide the strongest concern for cancer risk whereas certain animal proteins, especially fish, may actually be protective.

  • First and foremost include a large variety of colorful fruits and vegetables in your diet.
  • Next, vary your protein sources, including plant based sources of protein (beans, lentils, nuts, seeds) on a regular basis.
    • Aim to have fish 2 or more times per week the fattier the better.
    • Poultry, without the skin, would be your next best option.
    • Limit eggs to 1 or 2 times per week soft and hard boiled will be a better option than scrambled or fried. Consider avoiding eggs completely if you have had a reproductive cancer or are at high-risk for breast, ovarian, and prostate cancer.
    • Limit red meat to once a week or less and avoid cooking at high temperatures.
    • Grass fed and pasture raised animals produce meat, dairy, and eggs that are naturally lower in cholesterol and higher in omega-3s, thus reducing the inflammatory potential of the food. In the research we reviewed, there have been no studies comparing the cancer causing risk of grass-fed versus conventionally fed meats.
    • Keep the heat below 400 degrees Fahrenheit (200 degrees Centigrade).
    • HCA formation can also be substantially decreased by increasing the frequency of flipping during cooking limit the amount of time you leave the meat on the heat surface (16).
    • Choose cooking methods that avoid direct heat: steaming, poaching, stewing
    • Formation of HCA during cooking of beef, fish, or chicken can be decreased by marinating or brief microwave cooking before frying, broiling, or grilling (16).
    • Combining colorful vegetables with your meats provides good sources of calcium, chlorophyll, vitamin C, and polyphenols, all of which may reduce the negative effects of heme iron found in the meat (23).
    • Charred, fried, and processed meats.
    • Gravy made from meat drippings

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    45. Zheng JS, Hu XJ, Zhao YM, Yang J, Li D. Intake of fish and marine n-3 polyunsaturated fatty acids and risk of breast cancer: meta-analysis of data from 21 independent prospective cohort studies. BMJ (Clinical research ed) 2013346:f3706.

    46. Song J, Su H, Wang BL, Zhou YY, Guo LL. Fish consumption and lung cancer risk: systematic review and meta-analysis. Nutrition and cancer 201466:539-49.

    47. Jiang PY, Jiang ZB, Shen KX, Yue Y. Fish intake and ovarian cancer risk: a meta-analysis of 15 case-control and cohort studies. PLoS One 20149:e94601.

    48. Wu S, Feng B, Li K, et al. Fish consumption and colorectal cancer risk in humans: a systematic review and meta-analysis. The American journal of medicine 2012125:551-9 e5.

    49. Pham NM, Mizoue T, Tanaka K, et al. Fish consumption and colorectal cancer risk: an evaluation based on a systematic review of epidemiologic evidence among the Japanese population. Japanese journal of clinical oncology 201343:935-41.

    50. Luo J, Yang Y, Liu J, et al. Systematic review with meta-analysis: meat consumption and the risk of hepatocellular carcinoma. Alimentary pharmacology & therapeutics 201439:913-22.

    51. Huang RX, Duan YY, Hu JA. Fish intake and risk of liver cancer: a meta-analysis. PLoS One 201510:e0096102.


    Red meat consumption and breast cancer risk

    October 9, 2014 — Maryam S Farvid, a visiting scientist and Takemi fellow at Harvard School of Public Health, was first author on two recent studies that found that young women who ate higher amounts of red meat had a higher risk of breast cancer.

    Q: How strong of a link did you find between eating red meat and increased breast cancer risk?

    A: We found that women who ate the most red meat in adolescence or early adulthood had an increased risk of developing breast cancer later in life. One serving a day increment in red meat intake during adolescence was associated with a 22% higher risk of premenopausal breast cancer and each serving per day increment during early adulthood was associated with a 13% higher risk of breast cancer overall. Those who ate more poultry during the same period had a lower risk of developing breast cancer.
    Of course, red meat is not the only risk factor for breast cancer. And this is an observational study, so we could not say that eating red meat was the only reason these women got cancer. But our analysis took into account most of the known breast cancer risk factors, and we adjusted for smoking, alcohol intake, age, hormone therapy, and oral contraceptive use. Still, red meat was one of the important breast cancer risk factors.

    Q: Some previous studies have not found a link between red meat and breast cancer. How do you account for the discrepancy?

    A: The difference between our study and the other studies is the time period of measuring exposure. Most of the studies measured the diet of women in midlife or later. We looked at adolescence and early adulthood, because at that age mammary glands seem to be more susceptible to carcinogenic exposure.

    We developed this hypothesis based on the results from atomic bombings of Hiroshima and Nagasaki. Girls and young women who were exposed to this radiation had a higher risk of breast cancer later. But women who were exposed at age 40 or older did not have an increased risk.

    Also, women often decrease the amount of red meat they eat during middle age, so lower red meat at age 50 does not necessarily mean the women had a low intake in their 20s.

    Q: Based on your findings, what are your recommendations to women—and would they be different depending on the woman’s age?

    A: Women don’t have to become vegetarians and give up red meat. But if they decrease the amount of the red meat they eat—for example, having it once a week instead of twice a day—they will decrease their risk of developing breast cancer. The good news is that they can replace red meat with other sources of protein, including poultry, legumes, nuts, or fish. Women will get the most benefit if they do this earlier in life rather than later.

    And because red meat is not the only risk factor for risk of breast cancer, we suggest that women adopt a healthy lifestyle: drink less alcohol, don’t smoke, and get some physical activity.


    Preventing Cancer

    Although 1 in 5 men and 1 in 6 women worldwide develop some type of cancer during their lifetime, those diagnosed are living longer than ever, thanks to screening and early detection, vaccinations, and improvements in treatment. However, even for cancers with effective treatment options, prevention has the greatest potential to reduce the burden of cancer in the general population. [1]

    Because each person is exposed to unique environmental and lifestyle factors, cancer risk can vary. Although some factors cannot be controlled (such as inherited genetic mutations), there is a range of modifiable environmental and lifestyle factors that can help reduce the risk of developing cancer.

    According to the World Health Organization (WHO), a 30-40% cancer burden can be attributed to lifestyle risk factors such as tobacco smoking, alcohol consumption, a diet low in fruit and vegetables, overweight and obesity, and physical inactivity. [2] In a 2018 report by the World Cancer Research Fund (WCRF) and the American Institute of Cancer Research (AICR), not-for-profit organizations that lead a network of cancer prevention charities with a global reach, 10 cancer prevention recommendations on diet and nutrition were developed. These recommendations were based on the continuous update project of evidence in cancer research, which summarizes current evidence with relevant papers from randomized controlled trials and cohort studies. [3] Taken together, they promote a lifestyle consisting of a healthy dietary pattern, physical activity, and weight management. This may not only help reduce the risk of cancer but may also contribute to the prevention of obesity and other chronic diseases such as type 2 diabetes and cardiovascular disease.

    Here is a closer look at some of their recommendations:

    Maintain a healthy weight

    In a meta-analysis conducted by the WCRF/AICR, there is convincing evidence that carrying extra fat mass, marked by a higher body mass index (BMI), greater waist circumference, and greater waist-to-hip ratio, significantly increases the risk of several cancers: [4]

    • BMI measures one’s weight in relation to height. A BMI between 18.5-25 is classified as normal, 25.1-29.9 overweight, and 30 or higher obese. Each increase of 5 points in BMI was associated with a 50% higher risk of endometrial cancer, 48% higher risk of esophageal adenocarcinoma, 30% higher risk of kidney cancer, 30% higher risk of liver cancer, 12% higher risk for postmenopausal breast cancer, 10% higher risk of pancreatic cancer, and 5% higher risk of colorectal cancer.
    • Each 4-inch increase in waist circumference was shown to increase the risk of esophageal adenocarcinoma by 34%, pancreatic cancer by 11%, postmenopausal breast cancer by 11%, kidney cancer by 11%, endometrial cancer by 5%, and colorectal cancer by 2%.
    • A waist-to-hip ratio (WHR) measures one’s waist size divided by hip size. People who carry more weight in the belly (apple shape) are at higher risk for cancer and other chronic diseases than those who carry more weight in the hips (pear shape). The WHO recommends a healthy WHR to be 0.9 or less in men and 0.85 or less in women. Each 0.1 unit increase in waist-hip ratio significantly increased the risk of esophageal adenocarcinoma by 38%, kidney cancer by 26%, endometrial cancer by 21%, pancreatic cancer by 19%, postmenopausal breast cancer by 10%, and colorectal cancer by 2%.

    Significant increasing weight in adult life is a convincing cause of postmenopausal breast cancer and endometrial cancer.

    • Each 11-pound increase in weight gain during adulthood was significantly associated with a 16% higher risk of endometrial cancer, and 6% higher risk of postmenopausal breast cancer.

    Incidence of obesity-related cancers is also rising in young adults. Researchers from the American Cancer Society collected data from 25 state cancer registries for people ages 25-84 years diagnosed with any cancer from 1995 to 2014. [5] Over this time period, incidence rates of several obesity-related cancers—including colorectal, kidney, and pancreatic—increased significantly in the youngest age group, ages 25-49 years (with the sharpest increases in progressively younger ages). Although the incidence of these cancers also rose in older age groups, the rate of increase was much smaller.

    Be physically active

    Physical activity is defined as any movement that uses skeletal muscles and requires more energy than does resting. Physical activity can include working, exercising, performing household chores, and leisure-time activities such as walking, jogging, running, yoga, hiking, bicycling, and swimming.

    There is evidence from a 2009 meta-analysis of 52 epidemiologic studies showing that the most physically active individuals had a 24% lower risk of colon cancer than those who were the least physically active. [6] A 2013 meta-analysis of 31 prospective studies showed that the average breast cancer risk reduction associated with physical activity was 12%, and the protective effect was stronger for postmenopausal women. [7] After menopause, women who increase their physical activity may also have a lower risk of breast cancer than women who do not. [8]

    Sedentary behaviors, such as spending an extended amount of time sitting, reclining, or lying down, may also increase cancer risk. [9] The review of research on sedentary behavior and risk of endometrial, colon, and lung cancers found that the highest versus lowest levels of sedentary time increased risks of these cancers by a statistically significant range of 20-35%. [10]

    Eat a healthful diet

    An overall healthy dietary pattern has the potential to lower cancer risk by 10-20%. [11] The association between diet and cancer incidence varies by cancer sites and also by sex, [12] but the recommended components of a healthy diet are often similar. The WCRF/AICR listed the following dietary recommendations to protect against cancer:

    • Limit alcohol consumption. [13] There is strong evidence that consumption of alcoholic drinks is a cause of cancers of the mouth, pharynx and larynx, esophagus (squamous cell carcinoma), liver, colorectum, and breast (particularly postmenopause). Every 10 grams of alcohol (as ethanol) consumed per day elevated the risks of these cancers by 4-25%. The evidence shows that alcoholic drinks of all types have a similar impact on cancer risk. This recommendation therefore covers all types of alcoholic drinks, whether beer, wine, spirits (liquors), or any other alcoholic drinks, as well as other alcohol sources.
    • Eat a diet rich in whole grains, vegetables, fruit, and beans. [14] Make whole grains, vegetables, fruit, and pulses (legumes) such as beans and lentils a major part of your daily diet. There is strong evidence that eating whole grains protects against colorectal cancer, and that eating foods containing dietary fiber protects against colorectal cancer, weight gain, overweight, and obesity, which, as described above, increases the risk of many cancers.
    • Limit “fast” foods. [15] Fast foods are readily available convenience foods that tend to be energy-dense and are often consumed in large portions. Most of the evidence on fast foods is from studies looking at burgers, fried chicken, French fries, and high-calorie drinks (containing sugar, such as soda or unhealthy fats, such as shakes). There is strong evidence that diets containing higher amounts of fast foods and other processed foods high in unhealthy fats, starches, or sugars, as well as consuming a “Western type” diet (characterized by a high amount of added sugars, meat, and fat), are causes of weight gain, overweight, and obesity, which are a risk factor for many cancers.
    • Limit red and processed meat. [16,17] Red meat includes all types of muscle meat from a mammal, including beef, veal, pork, lamb, mutton, horse, and goat. Processed meat has been transformed through salting, curing, fermentation, smoking, or other processes to enhance flavor or improve preservation. Although these products are often made from red meat (i.e., ham, salami, bacon, and some sausages such as frankfurters and chorizo), other meats can also be processed (i.e., turkey bacon, chicken sausage, and deli-sliced chicken). While both red and processed meat were suggested to increase the risk of a number of other cancers, the evidence was most convincing for colorectal cancer. The risk of colorectal cancer increased by 16% with every 50g/day of processed meat intake, and by 12% with every 100g/day of red meat intake. Because meat can be a valuable source of nutrients, in particular protein, iron, zinc, and vitamin B12, the recommendation is to limit rather than completely avoid minimally processed red meat. However, poultry and seafood are generally healthier sources of protein as well as many of these other nutrients. Very little, if any, processed meat should be consumed.
    • Limit sugar-sweetened drinks. [18] There is convincing evidence that sugar-sweetened drinks is a cause of weight gain, overweight, and obesity in both children and adults, especially when consumed frequently or in large portions. As noted above, obesity increases the risk of many cancers.

    Avoiding tobacco and excess sun exposure

    The recommendations also emphasize that not smoking and avoiding other exposure to tobacco and excess sun are also important in reducing cancer risk.

    Cancer survivorship

    Although evidence is not strong enough to reach firm conclusions, there are indications of links between lifestyle factors and cancer survivorship with improved quality of life and longer survival, especially for more common cancers. For example, maintaining a healthy weight, being physically active, eating foods containing fiber, and having a lower intake of saturated fat appear to lead to better survival after a breast cancer diagnosis.[14] Unless otherwise advised, and if they can, all cancer patients and survivors are advised to follow the WCRF/AICR Cancer Prevention Recommendations as long as possible after the acute stage of treatment.

    These recommendations are also helpful for managing or preventing other chronic diseases after a cancer diagnosis. A study of survivors of the 20 most common cancers revealed that, even after controlling for the overlapped risk factors for cancer and cardiovascular disease such as excessive weight and smoking, survivors of most site-specific cancers had an increased risk for cardiovascular diseases compared with that of the general population. [15] Evidence has shown that certain cancer treatments, for example anthracycline and trastuzumab, can lead to a higher risk of disease and death from cardiovascular complications. [16-18]

    Related

    1. WHO – International Agency for Research on Cancer. “Latest global cancer data: Cancer burden rises to 18.1 million new cases and 9.6 million cancer deaths in 2018.” https://www.who.int/cancer/PRGlobocanFinal.pdf
    2. Ullrich A. Cancer Control: Knowledge Into Action: WHO Guide for Effective Programmes. World Health Organization, 2007.
    3. World Cancer Research Fund/American Institute for Cancer Research. Continuous Update Project Expert Report 2018. “Recommendations and public health and policy implications.“
    4. World Cancer Research Fund/American Institute for Cancer Research. Continuous Update Project Expert Report 2018. “Body fatness and weight gain and the risk of cancer.“
    5. Sung H, Siegel RL, Rosenberg PS, Jemal A. Emerging cancer trends among young adults in the USA: analysis of a population-based cancer registry. The Lancet Public Health. 2019 Mar 14(3):e137-47.
    6. Wolin KY, Yan Y, Colditz GA, Lee IM. Physical activity and colon cancer prevention: a meta-analysis. British journal of cancer. 2009 Feb100(4):611-6.
    7. Wu Y, Zhang D, Kang S. Physical activity and risk of breast cancer: a meta-analysis of prospective studies. Breast cancer research and treatment. 2013 Feb137(3):869-82.
    8. Eliassen AH, Hankinson SE, Rosner B, Holmes MD, Willett WC. Physical activity and risk of breast cancer among postmenopausal women. Archives of internal medicine. 2010 Oct 25170(19):1758-64.
    9. Tremblay MS, Aubert S, Barnes JD, Saunders TJ, Carson V, Latimer-Cheung AE, Chastin SF, Altenburg TM, Chinapaw MJ. Sedentary behavior research network (SBRN)–terminology consensus project process and outcome. International Journal of Behavioral Nutrition and Physical Activity. 2017 Dec14(1):1-7.
    10. 2018 Physical Activity Guidelines Advisory Committee. 2018 Physical Activity Guidelines Advisory Committee Scientific Report. Washington, DC: U.S. Department of Health and Human Services, 2018.
    11. Schwingshackl L, Hoffmann G. Diet quality as assessed by the Healthy Eating Index, the Alternate Healthy Eating Index, the Dietary Approaches to Stop Hypertension score, and health outcomes: a systematic review and meta-analysis of cohort studies. Journal of the Academy of Nutrition and Dietetics. 2015 May 1115(5):780-800.
    12. Grosso G, Bella F, Godos J, Sciacca S, Del Rio D, Ray S, Galvano F, Giovannucci EL. Possible role of diet in cancer: Systematic review and multiple meta-analyses of dietary patterns, lifestyle factors, and cancer risk. Nutrition reviews. 2017 Jun 175(6):405-19.
    13. Ervik M, Lam F, Ferley J, et al. Cancer Today. 2016. International Agency for Research on Cancer. Available from http://gco.iarc.fr/taody . Accessed on 2019/4/15.
    14. World Cancer Research Fund/American Institute for Cancer Research. Continuous Update Project Expert Report 2018. “Diet, nutrition, physical activity and breast cancer survivors.“
    15. Strongman H, Gadd S, Matthews A, Mansfield KE, Stanway S, Lyon AR, dos-Santos-Silva I, Smeeth L, Bhaskaran K. Medium and long-term risks of specific cardiovascular diseases in survivors of 20 adult cancers: a population-based cohort study using multiple linked UK electronic health records databases. The Lancet. 2019 Sep 21394(10203):1041-54.
    16. Mehta LS, Watson KE, Barac A, Beckie TM, Bittner V, Cruz-Flores S, Dent S, Kondapalli L, Ky B, Okwuosa T, Piña IL. Cardiovascular disease and breast cancer: where these entities intersect: a scientific statement from the American Heart Association. Circulation. 2018 Feb 20137(8):e30-66.
    17. Bowles EJ, Wellman R, Feigelson HS, Onitilo AA, Freedman AN, Delate T, Allen LA, Nekhlyudov L, Goddard KA, Davis RL, Habel LA. Risk of heart failure in breast cancer patients after anthracycline and trastuzumab treatment: a retrospective cohort study. Journal of the National Cancer Institute. 2012 Sep 5104(17):1293-305.
    18. McGowan JV, Chung R, Maulik A, Piotrowska I, Walker JM, Yellon DM. Anthracycline chemotherapy and cardiotoxicity. Cardiovascular drugs and therapy. 2017 Feb 131(1):63-75.

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    Red meat vs. processed meat

    When it comes to red meat and processed meat, which one should you think twice about when it comes to feeding yourself and your family?

    The IARC classifies red meat as a Group 2A carcinogen, which is described as ‘probably carcinogenic to humans’.

    “This was based on limited evidence that eating red meat causes cancer in humans and strong evidence supporting a carcinogenic effect,” Dr. Khorana says. “Previous studies also have shown that grilling or smoking meat can create suspected carcinogens.”

    However, processed meat was classified as a Group 1, which means it’s carcinogenic to humans, and is in the same group as tobacco and alcohol. When something is classified as Group 1, that means there is sufficient evidence of carcinogenicity in humans, according to the report.

    The agency made no specific dietary recommendations and said it did not have enough data to define how much processed meat is too dangerous. But it said the risk rises with the amount consumed — each 50 gram portion of processed meat eaten daily increases the risk of colorectal cancer by 18%. To put that in perspective, 50 grams of bacon is roughly 3.5 slices.​

    “It’s important to know that this classification merely shows the level of confidence the IARC has in its belief that processed meat causes cancer,” he says. “And not how much cancer that processed meat causes or how potent a carcinogen it is. And so, hot dogs are not equally as dangerous as cigarettes — the two only share a confirmed link to cancer, in the IARC’s opinion.”

    Experts have long warned of the dangers of certain chemicals used to cure meat, such as nitrites and nitrates, which the body converts into cancer-causing compounds. The evidence so far suggests that it’s probably the processing of the meat, or chemicals naturally present within it, that increases cancer risk.

    “Processed meats fall into the same category that cigarette smoking does with lung cancer,” says Dr. Khorana. “In other words, it’s an item that causes cancer at some point in the future if you consume high amounts.”

    While the IARC said red meat contains some important nutrients, it still noted that red meat has an established link to colon, prostate and pancreatic cancers.


    RELATED ARTICLES

    HEART DISEASE: THE WORLD'S BIGGEST KILLER

    The world's biggest killer is ischaemic heart disease, responsible for 16 per cent of the world's total deaths.

    Since 2000, the largest increase in deaths has been for this disease, rising by more than 2 million to 8.9 million deaths in 2019.

    Stroke and chronic obstructive pulmonary disease are the 2nd and 3rd leading causes of death, responsible for approximately 11 per cent and 6 per cent of total deaths respectively.

    Only last month did another team of researchers from Canada link cardiovascular disease events, like heart attack and stroke, with processed meat consumption.

    A 2018 study, meanwhile, found regular consumption of red meat can raise levels of a cardiovascular disease-causing chemical more than 10 times.

    The organic compound – TMAO (trimethylamine N-oxide) – is produced in the gut during digestion.

    'Previous studies have shown links between greater red meat consumption and increased risk of heart attacks or dying from heart disease,' said study author Dr Zahra Raisi-Estabragh of Queen Mary University of London.

    'For the first time, we examined the relationships between meat consumption and imaging measures of heart health.

    'This may help us to understand the mechanisms underlying the previously observed connections with cardiovascular disease.'

    The study included 19,408 participants of the UK Biobank – a long-term study investigating the contribution of genes and the environment to the development of health problems.

    The researchers examined associations of self-reported intake of red and processed meat with heart anatomy and function.

    Cardiovascular disease (CVD) is a general term for conditions affecting the heart or blood vessels. CVD events include heart disease and stroke. All heart diseases are cardiovascular diseases, but not all cardiovascular diseases are heart disease

    THE THREE HEART MEASURES

    1. Cardiovascular magnetic resonance (CMR) assessments of heart function used in clinical practice such as volume of the ventricles and measures of the pumping function of the ventricles

    2. Novel CMR radiomics used in research to extract detailed information from heart images such as shape and texture (which indicates health of the heart muscle)

    3. Elasticity of the blood vessels (stretchy arteries are healthier)

    Three types of heart measures were analysed – one of which was the elasticity of the blood vessels, which is a sign of good health.

    The analysis was adjusted for other factors that might influence the association, including age, sex, deprivation, education, smoking, alcohol, exercise, high blood pressure, high cholesterol, diabetes and body mass index (BMI) as a measure of obesity.

    The researchers found that greater intake of red and processed meat was associated with declined measures of heart health across all measures studied.

    Specifically, individuals with higher meat intake had smaller ventricles, poorer heart function and stiffer arteries – all markers of worse cardiovascular health.

    As a comparison, the researchers also tested the relationships between heart imaging measures and intake of oily fish, which has previously been linked with better heart health.

    They found that as the amount of oily fish consumption rose, heart function improved and arteries were stretchier.

    'The findings support prior observations linking red and processed meat consumption with heart disease and provide unique insights into links with heart and vascular structure and function,' said Dr Raisi-Estabragh.

    Interestingly, the links between the three heart health measures and meat intake were only partially explained by high blood pressure, high cholesterol, diabetes and obesity.

    'It has been suggested that these factors could be the reason for the observed relationship between meat and heart disease,' said Dr Raisi-Estabragh.

    'For example, it is possible that greater red meat intake leads to raised blood cholesterol and this in turn causes heart disease.

    'Our study suggests that these four factors do play a role in the links between meat intake and heart health, but they are not the full story.'

    Dr Raisi-Estabragh noted that the study did not look into alternative mechanisms, and admitted that it did not establish casualty – that red meat causes a decline in heart function.

    'This was an observational study and causation cannot be assumed, but in general, it seems sensible to limit intake of red and processed meat for heart health reasons,' Dr Raisi-Estabragh said.

    Replacing red meat in our diet with plant-based alternatives will improve human health and planetary health, one expert claims

    The research is being presented at ESC Preventive Cardiology 2021, an online scientific congress of the European Society of Cardiology (ESC), which runs from Thursday to Saturday this week.

    Dr Shireen Kassam, a haematologist and senior lecturer at King’s College Hospital who was not involved with the research, said 'several decades worth' of observational data already shows eating red and processed meat increases the risk of developing and dying from coronary heart disease and heart failure.

    'It’s no surprise that participants consuming the most meat had evidence of impaired heart and blood vessel function,' she told MailOnline.

    'The study confirms that we must move away from questioning the role of red and processed meat in the diet and act upon these research findings by focusing on effective and honest public health messaging to support citizens to remove these foods from the diet and replace them with healthier plant-based sources of protein.

    'This will not only improve human health but has co-benefits for planetary health.'

    Dr Kassam is also the founder of Plant-Based Health Professionals UK, a non-profit dedicated to promoting plant-based food options.

    SHOULD YOU CUT BACK ON RED MEAT? WHAT THE EVIDENCE SAYS

    Meat is a good source of protein, vitamins and minerals in the diet.

    The Department of Health advises that we eat no more than 70g (cooked weight) of red and processed meat a day, which is the average daily consumption in the UK.

    This is mainly because there is a link between bowel cancer and red meat, such as beef and lamb, and processed meat, such as sausages and bacon.

    A 2011 report called Iron and Health from the Scientific Advisory Committee on Nutrition (SACN) assessed evidence on the link between bowel cancer and iron - meat is the main source of iron.

    SACN concluded that eating a lot of red and processed meat probably increases the risk of bowel cancer, and advised accordingly.

    The American Institute for Cancer Research advises we consume no more than three portions of red meat a week and urges us to 'avoid' processed meats.

    Processed meat often contains nitrogen-based preservatives that stop it going off while being transported or stored.

    These preservatives have been linked to both bowel and stomach cancer.

    When red meat is digested, the pigment haem gets broken down in our gut to form chemicals called N-nitroso compounds.

    These compounds have been found to damage the DNA of cells that line our digestive tract, which could trigger cancer.

    Our body may also react to this damage by making cells divide more rapidly to replace those that are lost.

    This 'extra' cell division may increase the risk of cancer.

    Cancer Research UK says three chemicals in meat are linked to bowel cancer because they damage cells in the gut.

    Red and processed meat has also been linked to type 2 diabetes.

    This may be due to the preservatives used or the meats' higher levels of saturated fat than chicken and fish.

    However, researchers in Canada, Spain and Poland cast a shadow over eating advice adopted by health organisations around the world in November 2019.

    In a landmark paper, the academics analysed past studies of how eating meat affected the health of more than four million people.

    The research, published in the journal Annals of Internal Medicine, found no evidence that eating beef, pork and lamb could increase the rates of heart disease, cancer, stroke or type 2 diabetes – despite fears.


    Chemicals in Meat Cooked at High Temperatures and Cancer Risk

    What are heterocyclic amines and polycyclic aromatic hydrocarbons, and how are they formed in cooked meats?

    Heterocyclic amines (HCAs) and polycyclic aromatic hydrocarbons (PAHs) are chemicals formed when muscle meat, including beef, pork, fish, or poultry, is cooked using high-temperature methods, such as pan frying or grilling directly over an open flame (1). In laboratory experiments, HCAs and PAHs have been found to be mutagenic—that is, they cause changes in DNA that may increase the risk of cancer.

    HCAs are formed when amino acids (the building blocks of proteins), sugars, and creatine or creatinine (substances found in muscle) react at high temperatures. PAHs are formed when fat and juices from meat grilled directly over a heated surface or open fire drip onto the surface or fire, causing flames and smoke. The smoke contains PAHs that then adhere to the surface of the meat. PAHs can also be formed during other food preparation processes, such as smoking of meats (1).

    HCAs are not found in significant amounts in foods other than meat cooked at high temperatures. PAHs can be found in other smoked foods, as well as in cigarette smoke and car exhaust fumes.

    What factors influence the formation of HCA and PAH in cooked meats?

    The formation of HCAs and PAHs varies by meat type, cooking method, and “doneness” level (rare, medium, or well done). Whatever the type of meat, however, meats cooked at high temperatures, especially above 300 ºF (as in grilling or pan frying), or that are cooked for a long time tend to form more HCAs. For example, well-done, grilled, or barbecued chicken and steak all have high concentrations of HCAs. Cooking methods that expose meat to smoke contribute to PAH formation (2).

    HCAs and PAHs become capable of damaging DNA only after they are metabolized by specific enzymes in the body, a process called “bioactivation.” Studies have found that the activity of these enzymes, which can differ among people, may be relevant to the cancer risks associated with exposure to these compounds (3–9).

    What evidence is there that HCAs and PAHs in cooked meats may increase cancer risk?

    Studies have shown that exposure to HCAs and PAHs can cause cancer in animal models (10). In many experiments, rodents fed a diet supplemented with HCAs developed tumors of the breast, colon, liver, skin, lung, prostate, and other organs (11–16). Rodents fed PAHs also developed cancers, including leukemia and tumors of the gastrointestinal tract and lungs (17). However, the doses of HCAs and PAHs used in these studies were very high—equivalent to thousands of times the doses that a person would consume in a normal diet.

    Population studies have not established a definitive link between HCA and PAH exposure from cooked meats and cancer in humans. One difficulty with conducting such studies is that it can be difficult to determine the exact level of HCA and/or PAH exposure a person gets from cooked meats. Although dietary questionnaires can provide good estimates, they may not capture all the detail about cooking techniques that is necessary to determine HCA and PAH exposure levels. In addition, individual variation in the activity of enzymes that metabolize HCAs and PAHs may result in exposure differences, even among people who ingest (take in) the same amount of these compounds. Also, people may have been exposed to PAHs from other environmental sources, not just food.

    Numerous epidemiologic studies have used detailed questionnaires to examine participants’ meat consumption and cooking methods (18). Researchers found that high consumption of well-done, fried, or barbecued meats was associated with increased risks of colorectal (19–21), pancreatic (21–23), and prostate (24, 25) cancer. However, other studies have found no association with risks of colorectal (26) or prostate (27) cancer.

    In 2015, an independent panel of experts convened by the International Agency for Research on Cancer (IARC) determined consumption of red meat to be “probably carcinogenic to humans” (Group 2A), based largely on data from the epidemiologic studies and on the strong evidence from mechanistic studies. However, IARC did not conclude that HCAs and PAHs were associated with cancer incidence.

    Do guidelines exist for the consumption of food containing HCAs and PAHs?

    Currently, no Federal guidelines address the consumption of foods containing HCAs and PAHs. The World Cancer Research Fund/American Institute for Cancer Research issued a report in 2007 with dietary guidelines that recommended limiting the consumption of red and processed (including smoked) meats however, no recommendations were provided for HCA and PAH levels in meat (28).

    Are there ways to reduce HCA and PAH formation in cooked meats?

    Even though no specific guidelines for HCA/PAH consumption exist, concerned individuals can reduce their exposure by using several cooking methods:

    • Avoiding direct exposure of meat to an open flame or a hot metal surface and avoiding prolonged cooking times (especially at high temperatures) can help reduce HCA and PAH formation (29).
    • Using a microwave oven to cook meat prior to exposure to high temperatures can also substantially reduce HCA formation by reducing the time that meat must be in contact with high heat to finish cooking (29).
    • Continuously turning meat over on a high heat source can substantially reduce HCA formation compared with just leaving the meat on the heat source without flipping it often (29).
    • Removing charred portions of meat and refraining from using gravy made from meat drippings can also reduce HCA and PAH exposure (29).

    What research is being conducted on the relationship between the consumption of HCAs and PAHs and cancer risk in humans?

    Researchers in the United States are currently investigating the association between meat intake, meat cooking methods, and cancer risk. Ongoing studies include the NIH-AARP Diet and Health Study (19, 30), the American Cancer Society’s Cancer Prevention Study II (31), the Multiethnic Cohort (6), and studies from Harvard University (32). Similar research in a European population is being conducted in the European Prospective Investigation into Cancer and Nutrition (EPIC) study (33).

    Selected References

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    What does this mean for me?

    The evidence is clear that eating less processed and red meat can help reduce the risk of bowel cancer, the 4th most common cancer in the UK.

    Eating less can make a difference, but it’s important to think about doing this as part of a healthy diet overall, along with being active.

    “The most important diet related risk factors for cancer are obesity and alcohol, which both increase risk of many types of cancer, and cause more cases than red and processed meat,” says Key.

    And he notes that diet has other health impacts beyond bowel cancer risk.

    “For example, meat can be an important source of iron so if someone is thinking about giving up meat all together they need to think about other sources of this,” he says.

    So, although this evidence doesn’t suggest we need to ditch processed and red meat altogether, it does serve as a reminder to think about how much we’re eating, and how often.

    Katie Patrick is a health information officer at Cancer Research UK