Thursday, 7 April 2016
On second thoughts, that vegetarian genomic study did show that not eating animals is not good for you.
Generally, a study that purported to show that vegan and vegetarian diets are harmful would be welcomed by meat eaters, who get a lot of pseudoscientific criticism from members of those groups, some of it disguised as sober science.
But no-one was much impressed by the Pune vs. Kansas study. Even Tom Naughton wrote it off as meaning the same thing the head of the NZ vegetarian society said it meant - that omega-6 seed oils just aren't good for us anyway.
But I thought about this, and, not so fast.
Seed oils high in omega 6 are harmful for the descendants of long lines of vegetarians because such people, because of an adaptation to the virtual absence, from their diets, of DHA and AA (arachidonic acid), the very long-chain PUFAs found in animal flesh and organ meats, have a more efficient version of the genes involved in synthesizing these fats from alpha-linolenic acid (ALA) and linoleic acid (LA). Too much LA overwhelms these enzymes, which only seem to be loosely regulated, and results in an excess of inflammatory AA products and an inadequacy of very long chain omega 3s.
So this adaptation is good for vegetarians eating traditional diets, as in Pune where the traditional fat source would have been ghee, with a little mustard seed oil added. Low in omega 6, balanced in omega 3, enough hearty saturated dairy fat to protect against the diabetogenic effect of a diet high in both starch and sugar.
But think about it - this adaptation isn't some random lucky fluke. For one gene to dominate over another like this, there needs to be some significant and sustained reproductive advantage.
Reproductive advantage means one or more of these - greater fertility, fewer stillbirths, fewer complications of pregnancy, lower mortality early in life, greater attractiveness to a mate.
The vegetarian PUFA polymorphism flourished because, in the past, people without it, eating vegetarian diets, suffered some combination of infertility, stillbirth, dangerous pregnancy, early mortality, or plain butt-ugliness.
Its incidence at present is 70% in South Asians, 53% in Africans, 29% in East Asians, and 17% in Europeans. That to me indicates a burden of suffering and infertility in South Asians in the past, to produce this result - that's how evolution works, that's how Nature selects. If you're European, the chances are that you do need AA and DHA in your food, unless you want to take your chances with lots of vegetable oil - which seems to me a very second-rate, artificial, and dicey way of getting there.
Note that some vegans do think it's okay to eat bivalve shellfish, which can't feel pain (or rather, probably don't feel more pain that plants do, but who knows what that is). This would supply more than enough DHA and AA. However, PETA takes the hard line on this, like the Buddhist who won't swat a zika-carrying mosquito.
But then, PETA is Neal Barnard's baby and he's a dietary cholesterol zealot, so their ban on shellfish might not be as strictly ethical as they claim. Dr Barnard "advises people to avoid added vegetable oils and other high-fat foods as well as refined sugar and flour". Well good for him but it is hard to see where the AA and DHA will come from for the majority of Europeans on this diet.
Maybe veganism is a bit like statinism - enough of the people it's going to harm will drop out of the trial early for the long-term results to look a bit encouraging. It would be interesting to see if long-term vegans in European populations have in fact self-selected for the FADS2 polymorphism common in Pune.