[liamona]

Originally Posted by WhiteCrow

You do know that research like this doesn't say ****?

Correlation is not the same as causation.

That's basically what Dr. Briffa said on his blog:

Don’t be fooled by the study which found lower cancer rates in vegetarians | Dr Briffa's Blog

I do not dismiss this evidence out of hand, but I think it is important to bear in mind that this study was epidemiological in nature, and can only then tell us about associations between diet and cancer. But just because two things are associated does not mean one is causing the other. The usual assumption with studies of this nature is that there’s something bad about meat that ups cancer risk. But it may be vegetables are cancer protective and vegetarians eat more of these. Or maybe it’s neither of these things. Or maybe, it’s nothing more than an association and eating meat/fewer vegetables does not cause cancer at all. We just don’t know.

One major problem with epidemiological studies is what are known as ‘confounding’ factors. So let’s say we find from a study less physically active people turn out to have a higher risk of lung cancer. We have found an association between two things that might cause people to conclude that a sedentary lifestyle causes lung cancer. But, imagine that sedentary people are more likely to smoke. Smoking is a potential confounding factor here, and may be the real reason for why sedentary individuals are at heightened risk of lung cancer. In epidemiological studies often an attempt is made to ‘control for’ potential confounding factors. It’s an imprecise science, for sure, but generally better than nothing.

Controlling for potential confounding factors is particularly important when comparing meat-eaters and vegetarians because, generally speaking, they are likely to be more health-conscious than meat-eaters. Meat-eating has an unhealthy reputation, right? And vegetarianism generally as a ‘healthy’ image too. So someone inclined to do what they can to protect or improve their health may be drawn towards eschewing meat. But these individuals may also be drawn to other habits too like smoking less and exercising more.

[...]

I read here that Professor Tim Key, the lead author of the study being reported on today “said it was impossible to draw strong conclusions from this one single study”. He is quoted as saying, “At the moment these findings are not strong enough to ask for particularly large changes in the diets of people following an average balanced diet.” Even the study’s lead author seems to have poured cold water on its findings. Perhaps Professor Key is aware of the evidence which shows vegetarianism does not offer distinct health advantages? He should be, seeing as he’s the lead author of the studies mentioned above [2,4] that show that vegetarians have mortality rates the same as non-vegetarians.

2. Key TJA, et al. Dietary habits and mortality in 11000 vegetarians and health conscious people: results of a 17 year follow up. Br Med J 1996;313:775–9


4. Key TJ, et al. Mortality in British vegetarians: results from the European Prospective Investigation into Cancer and Nutrition (EPIC-Oxford). Am J Clin Nutr. 2009;89(5):1613S-1619S