The more meat, the more cancer

People who eat little or no meat have lower rates of colorectal, breast and prostate cancer—and lower cancer risk overall than frequent meat-eaters. “This risk of overall cancer appears to be lowest for vegetarians, then pescatarians (fish-eaters), then low meat-eaters but whether this is due to dietary factors remains unclear,” said Cody Watling, lead author of a study on meat consumption and cancer risks. Results were published in BMC Medicine. Watling is a cancer epidemiology PhD student at the University of Oxford. Generally, it is still unclear how much dietary patterns are related to the risk of developing cancer. Plus, studies have lacked statistical power to detect an association of diet groups and cancers at specific sites, the study said. Read: Long lasting cell treatment cured leukemia patients: doctors It has been hypothesized that vegetarian diets may be associated with lower cancer risk due to the increased consumption of fruits, vegetables and whole grains. Indeed, some studies such as the EPIC-Oxford study suggested vegetarians and pescatarians may have lower risks for cancer overall than meat eaters. A prospective study was conducted to further understand the associations of dietary groups with overall cancer risk, and also specifically of colorectal, postmenopausal breast, and prostate cancer. “We focused on these three types of cancer as they are three of the most commonly diagnosed in the U.K. As well, due to the limited number of vegetarians and pescatarians in the study, we only assessed cancer types which had enough cases observed in the study to have adequate statistical power,” Watling told the Medical Post in an email. Researchers used data from the U.K.’s Biobank, a database launched in 2006 which includes long-term medical and genetic data from half a million volunteer participants. Biobank includes information on about 10,000 pescatarians, 8,000 vegetarians, and nearly 55,000 total incident cancer cases, to date. Regular meat-eaters were defined as those who ate processed, red meat or poultry more than five times a week. Low meat-eaters ate meat five times or less a week. Fish-eaters said they never consumed red meat or poultry. Vegetarians reported they did not eat any meat or fish, and this group also included a small number of vegans who also avoid dairy and eggs. Of the participants included in the analysis, 247,571 (52.4%) were regular meat-eaters, 205,385 (43.5%) were low meat-eaters, 10,696 (2.3%) were fish eaters and 8,685 (1.8%) were vegetarians. Details were based on responses to questionnaires. After an average of 11.4 years of follow-up, 54,961 incident cases of cancer (any type) were diagnosed. Of these; 5,882 participants had developed colorectal cancer, 7,537 women were diagnosed with postmenopausal breast cancer, and 9,501 men were diagnosed with prostate cancer. Vegetarians and fish-eaters (both sexes) tended to have lower BMIs, were younger, less likely to be ever smokers, have a higher education status, and drank less alcohol than the regular meat-eaters. Men who were vegetarian were also less likely to have had a PSA test in comparison to meat-eaters, the study said. When compared to regular meat-eaters, vegetarians had a statistically significant lower risk of all cancers, postmenopausal breast cancer, and prostate cancer. Fish-eaters also had a lower risk for all cancers and prostate cancer than regular meat eaters. Low meat-eaters had a lower risk of colorectal cancer than regular meat eaters. The vegetarian women in the study population had slightly lower BMI than regular meat-eaters and when BMI was adjusted for, the risk for vegetarian women compared to regular meat-eaters for postmenopausal breast cancer lost any statistically significance. “We know higher body weight after menopause is a risk factor for breast cancer and this did seem to potentially explain the observed difference for postmenopausal breast cancer amongst vegetarian women, but for the other cancers, this was not true. When BMI was adjusted, estimates only slightly changed for overall cancer or colorectal cancer or did not change at all in the case for prostate cancer,” Watling said. Men who were low meat-eaters, fish-eaters, or vegetarian all had a lower risk of colorectal cancer than regular meat-eaters. However, there was no significant association across diet groups for women and colorectal cancer. Prostate cancer rates were lower in men who were vegetarians or fish-eaters when compared to regular meat eaters. However, no risk difference was seen when they were compared to low meat-eaters. Generally, the risk for cancers overall was inversely associated with the amount of meat consumed—the less meat, the less cancer. “Physicians should recommend their patients limit the intake of processed and red meat in their diet, and promote a diet rich in whole grains, fruits, vegetables and beans, with emphasis on maintaining a healthy body weight,” Watling said. In general, the findings “are consistent with what we’ve seen over the past few decades,” said Rachel Murphy, PhD, an assistant professor in the School of Population and Public Health at the University of British Columbia. She was not involved in the study. But “the big step forward is they looked at these defined specific diets rather than an overall healthy diet,” she told the Medical Post in an interview. People who opt to be vegetarian or pescatarian tend to have healthier body weight and lifestyles, as well as lower rates of smoking which are risk factors for cancer. Greater plant consumption means increased intake of fibre and nutrients which help lower cancer risk. Murphy suggested a joint report Diet, Nutrition, Physical Activity and Cancer: a Global Perspective by the World Cancer Research Fund and the American Institute for Cancer Research for further details relating to cancer and diet. The World Health Organization lists red meat as probably carcinogenic and includes processed meat as well.

The more meat, the more cancer

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