Does eating meat really increase our risk of colon cancer?

I generally rate meat (including red meat) as a food for those who choose to eat it. However, I appreciate that not all health professionals share my enthusiasm for this food: often, individuals will remind us to eat ‘lean’ meat to avoid consuming so-called saturated fat that ’causes’ heart disease. Except, the evidence doesn’t really support this stance: most epidemiological studies do not support a link between saturated fat and heart disease, and there really is a distinct dearth of evidence suggesting that cutting back on saturated fat is beneficial to the heart (or has broad benefits for health for that matter).

The other common criticism levelled against meat is that it causes bowel cancer. Indeed there have been some studies that appear to show a link between meat-eating and an increased risk of this condition. However, such studies are epidemiological in nature, and therefore cannot be used to prove that it’s the meat that is a genuine problem in this regard.

Imagine for a moment that meat does NOT cause colon cancer. The any apparent association between meat and colon cancer might be down to, say, the fact that individuals who eat a lot of meat might also be more likely to exhibit more in the way of unhealthy behaviours such as cigarette smoking or a sedentary lifestyle. Also, focusing just on the diet for a moment, those eating more meat may end up eating less of other foods that might have a preventive role, such as fruits and vegetables. In other words, it may not be the presence of meat, but the absence of other foods, that causes the apparent link between meat and colon cancer.

Because of these factors, we need to be somewhat wary, I think, about concluding that meat causes colon cancer. And it should also be borne in mind that there is plenty of evidence that does not support an association. For example, a review of the available literature published in the European Journal of Clinical Nutrition found that of 44 relevant studies, most (31) found no apparent association between red meat intake and colon cancer risk [1].

All this might be worth bearing in mind when one considers the results of a study published on-line in the American Journal of Clinical Nutrition [2]. This study looked at the risk of cancer in individuals categorised as meat eaters, fish eaters (those who don’t eat meat but do eat fish), vegetarians (no animal foods other than eggs and/or dairy products) and vegans (no animal products).

Compared to those eating meat, vegetarians and vegans turned out to have an increased risk of colorectal (cancer in the colon or rectum). Risk in these people was 39 per cent higher than in meat eaters. They also compared risk of colorectal cancer in individuals classed as vegetarian (vegetarian and vegans) with non-vegetarians (eaters of meat and/or fish). Here, vegetarians had a 49 per cent increased risk of colorectal cancer.

The authors describe these findings as ‘surprising’, and suggest that the explanation for them might be partly due to chance or other dietary differences between the groups. However, you want to explain it, the findings of this study most certainly do not support the notion that meat-eating puts people in mortal terror of cancers in the large bowel.

And neither do the results of a study, also published on-line recently in the American Journal of Clinical Nutrition [3]. This review of several studies found no statistically significant association between either animal fat or animal protein intake and risk of colorectal cancer. It should be pointed out that this study received funding from the Cattlemen’s Beef Board and National Pork Board.

It seems from the science as it stands that there is good reason to challenge the commonly-held belief that eating meat increases the risk of bowel cancer.

References:

1. Truswell AS. Meat consumption and cancer of the large bowel. Eur J Clin Nut 2002;(suppl 1):S19-S24

2. Key TJ, et al. Cancer incidence in vegetarians: results from the European Prospective Investigation into Cancer and Nutrition (EPIC-Oxford). 2009;89(suppl):1S-7S

3. Alexander DD, et al. Meta-analysis of animal fat or animal protein and colorectal cancer. Am J Clin Nutr 2009;89:1-8