Vegetarians vs. Healthy Omnivores

The same reason it was so difficult to study cancer among coffee-drinkers is the same reason it’s so difficult to study cancer among meat-eaters. Even if they found lower cancer rates among those eating vegetarian, maybe it’s just because vegetarians exercise more, or smoke less, or inhale less diesel fumes, because they all own a Prius.

So, the way you get around that is you study a group of healthy meat-eaters who, for example, smoke just as infrequently as the group of vegetarians you’re trying to study—to equal things out, control for non-dietary factors. So, you don’t just classify people into meat-eaters, fish-only eaters, and vegetarians. You adjust for smoking—past smoking, current smoking, the amount of smoking, cigarette smoking, cigar smoking, pipe smoking, alcohol consumption, body mass index, physical activity level. And for women, how many children they’ve had—which can be protective against breast cancer; whether or not they were on the pill. Anything they could think of to factor everything else aside, and just focus in on what they were interested in—whether or not one eats meat.

Now controlling for obesity is not really fair to the vegetarians. We know that vegetarians are significantly more likely to be thin, which we know is protective against cancer. So, by comparing vegetarians only to thin meat-eaters, it undercuts one of the benefits of eating vegetarian. It effectively erases one of the reasons why eating vegetarian may reduce cancer rates. But they weren’t interested in indirect ways in which meat might cause cancer, like meat leading to obesity, leading to cancer. They wanted to study meat and cancer more directly.

And to do that, you have to handicap the vegetarians even further. Maybe the reason vegetarians are so healthy is not because they eat less meat, but because they eat more plants. So vegetarians were compared to meat-eaters, who, on average, ate about the same amount of fruits and vegetables every day. It may not have been easy, but they were able to dig up thousands of meat-eaters who ate four to five servings of fruits and veggies a day—about as much as the vegetarians were eating.

Again, this puts the vegetarians at a comparative disadvantage, by removing one of the key benefits of more plant-based diets, which is more plants. By comparing vegetarians to omnivores who don’t eat a lot of meat, and have a high fruit and vegetable intake, this could reduce the chance of observing lower cancer rates in the vegetarians. But they wanted to isolate out the meat component. So they did. They compared vegetarians only to healthy meat-eaters with healthier diets, and still, though there was onesurprising finding, which I’ll cover later, they still found the incidence of all cancers combined was lower among vegetarians.

To see any graphs, charts, graphics, images, and quotes to which Dr. Greger may be referring, watch the above video. This is just an approximation of the audio contributed by veganmontreal.

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• Key TJ, Appleby PN, Spencer EA, Travis RC, Allen NE, Thorogood M, Mann JI. Cancer incidence in British vegetarians. Br J Cancer. 2009 Jul 7;101(1):192-7.
• Key TJ, Appleby PN, Spencer EA, Travis RC, Roddam AW, Allen NE. Cancer incidence in vegetarians: results from the European Prospective Investigation into Cancer and Nutrition (EPIC-Oxford). Am J Clin Nutr. 2009 May;89(5):1620S-1626S.

Images thanks to Kukuruki and Paul-W via flickr

• cancer
• fruit
• meat
• obesity
• Plant-Based Diets
• smoking
• vegetables
• vegetarians
• weight loss