A couple of weeks ago, a new study came out, comparing forms of vegetarian diets with forms of meat-eating diets; the study itself is found here. Probably all readers of this blog are automatically a little skeptical when they see a splashy headline with new, strong advice that goes against the prevailing wisdom in fields of health and nutrition. Not that the so-called “prevailing wisdom” is always wise, or even prevailing– there’s lots of dissent and several conflicting theories about nutrition and health.
However, in the case the comparative benefits of vegetarian diets, compared with meat-eating ones, there is prevailing wisdom: vegetarian diets are generally better for us on multiple health and nutrition fronts.
Just to provide one (of hundreds) of standard reports that support the health benefits of vegetarian diets, check out this World Health Organization report from the International Agency for research on cancer. Here’s the bit that gets at the meat of the matter:
After thoroughly reviewing the accumulated scientific literature, a Working Group of 22 experts from 10 countries convened by the IARC Monographs Programme classified the consumption of red meat as probably carcinogenic to humans (Group 2A), based on limited evidence that the consumption of red meat causes cancer in humans and strong mechanistic evidence supporting a carcinogenic effect. This association was observed mainly for colorectal cancer, but associations were also seen for pancreatic cancer and prostate cancer.
So, meat is probably carcinogenic to humans. Well, that’s not good. Of course, real science and real science policy are nuanced, so here’s their summary recommendation:
These findings further support current public health recommendations to limit intake of meat,” says Dr Christopher Wild, Director of IARC. “At the same time, red meat has nutritional value. Therefore, these results are important in enabling governments and international regulatory agencies to conduct risk assessments, in order to balance the risks and benefits of eating red meat and processed meat and to provide the best possible dietary recommendations.
This is not really news, but of course good to hear from a knowledgeable and trustworthy source.
But then comes this new study, which was reported like this:
What? How could this be? Here’s what the news report said:
Interestingly, while there were positive benefits associated with vegetarianism, the group concludes the following:
Overall, our findings reveal that vegetarians report poorer health, follow medical treatment more frequently, have worse preventive health care practices, and have a lower quality of life… Our results have shown that vegetarians report chronic conditions and poorer subjective health more frequently.
They also discovered “significantly higher” incidences of cancer in vegetarians, as well as increased rates of anxiety disorder and depression, although they note that this is inconsistent with other research. They did point out another study which shows an increased risk of mental disorders in vegetarians. In general, vegetarians suffer from more chronic conditions and take more medication than even occasional meat eaters.
Wait a minute. Did the study REALLY show all this?
No. Not if you’re asking me. Or, rather, not if you’re asking some friends of mine who are much more familiar with the research on vegetarianism than I am (thanks, Angus and Bob!) One sent me a laundry list of problems with the original Austrian study. Here’s his list:
Problems with this study include:
- Small sample
- Lack of distinction between vegetarians for ideological reasons (e.g. animal suffering and environmental reasons) v those that may be vegetarian on medical advice or due to self-treatment due to pre-existing health conditions
- Many data points are subjective (self-declared)
- They make some weird claims (a Veg diet is ‘related to’ less frequent alcohol use)
- There are a huge number of confounders given the association of other factors related to veggie diets – I don’t think they are able to fully account for these – especially given sample size.
The other friend sent me these comments:
- First, there is — as the authors suggest — evidence pointing the other direction with respect to each of their specific conclusions. So that should adjust our confidence level a bit.
- Second, it’s pretty plausible that because foods aren’t fortified in a way that assumes that people are going to eat vegetarian or vegan, some less health-conscious vegetarians and vegans are going to suffer from nutritional deficits that will negatively impact their health. It isn’t clear how much of the effect this would explain, but it helps us think about the fact that there are political realities that are relevant to these nutritional studies.
- Third, the authors don’t consider the fact that some people may be switching to vegetarian vegan diets for health reasons — that is, because they have some health issue they are trying to address via dietary change, which suggests that they may well be less healthy than the average member of the population to begin with.
- Fourth, and most importantly, the authors of the study lump together strict vegans, vegetarians, and pescatarians. Given that many vegetarians and pescatarians eat diets that are still fairly heavy in animal products, it wouldn’t be surprising if any health benefits of a strict vegan diet were invisible in the data.