20% increased risk of death or disease over the span of a generation is not worth getting excited about? For someone who's healthy, it may seem insignificant when the baseline risk is low, but for someone who develops a chronic disease, in hindsight a 20% reduction may be very appealing. Minimizing regret is important.

As for scientific validity of those studies, doing proper scientific studies of diet is so difficult it might as well be impossible. What kind of person is going to volunteer to have someone else dictate their diet? What kind of person is going to comply with that diet long-term? If you want to do a blind study, you have to turn all food into unidentifiable mush. You can't have people seeing broccoli florets or pork chops.

There is a proposed theory for why red meat has those effects: Neu5gc consumption causing persistent low-level immune response. Less conclusive dietary studies have noted a difference, but without doing a scientific study giving one group Neu5gc supplements and another placebo, how can we know? Ethics boards might have a problem with that, since Neu5gc can be demonstrated in vitro to trigger an immune response.

Perhaps the most general and plausible theory is that it has nothing to do with inherent unhealthiness of red meat or meat in general. Rather, more meat consumption means less dietary fiber, fewer fruits and vegetables, assuming the same total caloric consumption. Meat consumption probably also correlates to excess calorie intake, which is a risk factor for a variety of chronic diseases.

> 20% increased risk of death or disease over the span of a generation is not worth getting excited about? For someone who's healthy, it may seem insignificant when the baseline risk is low, but for someone who develops a chronic disease, in hindsight a 20% reduction may be very appealing. Minimizing regret is important.T

You should read the article; the rest of the paragraph is as follows:

> So with lung cancer we could buy as a society the observation that cigarettes cause lung cancer because it was and remains virtually impossible to imagine what other factor could explain an association so huge and dramatic. Experiments didn’t need to be done to test the hypothesis because, well, the signal was just so big that the epidemiologists of the time could safely believe it was real. And then experiments were, in effect, done anyway. People quit smoking and lung cancer rates came down, or at least I assume they did. (If not, we’re in trouble here.) When I first wrote about the pseudoscience of epidemiology in Science back in 1995, “Epidemiology Faces It’s Limits”, I noted that very few epidemiologists would ever take seriously an association smaller than a 3- or 4-fold increase in risk. These Harvard people are discussing, and getting an extraordinary amount of media attention, over a 0.2-fold increased risk. (Horn-blowing alert: my Science article has since been cited by over 400 articles in the peer-reviewed medical literature, according to Thomson Reuter’s Web of Knowledge.)

The point is that we don't know if there's a 20% increase of risk if you start eating more red meat. We only know that the people who elected to do, and were sampled in the study (the top quintile), did have a 20% increase. There's a big difference here; statistics is subtle.

> As for scientific validity of those studies, doing proper scientific studies of diet is so difficult it might as well be impossible.

I agree, but then we should refrain from telling people that meat, and red meat in particular, is what's killing them. Especially when there are much more likely targets, like sugar.

If you blame sugar, you get the sugar lobby making similar arguments about poor scientific data for the proposition "sugar increases risk of diseases" that you're making against the proposition "red meat increases risk of diseases".

I think the main argument in favour of vegetarianism is neither nutritional nor ethical, but environmental.

I disagree. The vegetarians I know are more concerned about the handling and treatment of animals than the environment or their own health. And veganism's whole premise is based on the reduction of suffering.