A study of almost half a million British adults has found low or no meat diets are associated with reduced overall cancer risk, including for cancers outside the digestive system. Although the study cannot prove causation, the results hold whether or not an array of demographic and risk factors are taken into account.
Nutritional studies frequently produce conflicting results. Even aside from questions of researcher bias, it is hard to get people to stick to long-term randomly controlled dietary trials. Meanwhile, studies that only investigate people's self-reported diet after diagnosis pose problems of their own.
University of Oxford graduate student Cody Watling and colleagues couldn't address all these issues, but they did deal with one common concern about dietary research; small sample sizes. Watling used a sample of 472,377 British adults who reported the frequency of their meat and fish consumption. Comparing this data with an average of 11 years of health records. In BMC Medicine, they report 12 percent of the sample developed cancer over that period.
Just over half the sample (52 percent), reported eating meat five times a week or more, making for a neat cut-off point. Another 44 percent ate meat, but less frequently. Two percent did not eat any meat, and another 2 percent ate fish but not other animals.
The vegetarians and vegans had a 14 percent lower rate of cancer (equivalent to a 10.3 percent risk of cancer over the period). Those who consider that too challenging might take heart from the 10 percent lower cancer rate among the fish-eaters. Eating less meat provided a much smaller benefit – just 2 percent – but some in this group had only slightly lower meat intake.
The team also examined how diet related to cancers common enough to provide statistically useful samples.
Vegetarian or vegan men had a 31 percent lower rate of prostate cancer than those who ate meat regularly, a fact you can expect to see widely publicized by animal activists quite soon. Even those who ate fish, but not other meats, were at a 20 percent lower risk in that organ.
Post-menopausal vegetarian women had an 18 percent lower risk of breast cancer than their carnivorous counterparts, a result the authors potentially attribute to their generally lower Body Mass Indexes.
In keeping with past research, the authors also found a clear association between a low meat diet and fewer colorectal cancers – 9 percent less for the occasional meat eaters. However, the difference here was only statistically significant for men.
The authors acknowledge studies like this, however large their sample, cannot prove causality. It's possible some other factor that co-varies with diet explains the lower rates of cancer. However, they controlled for obvious possibilities like education, ethnicity, and cigarette and alcohol consumption, and found only marginal differences.
Even if diet is the magic ingredient, the authors also note we can't be sure, based on this data alone, whether meat consumption causes the cancer, or if foods that commonly replace meat like fruits and vegetables are protective.
The findings appear to contradict a widely covered study earlier this weak that found meat is associated with longer life expectancy worldwide. However, most people consuming a low-meat diet globally are doing so out of poverty, rather than replacing meat with adequate plant-based nutrition, which surely justifies separate categories.