Omega 3 fats and the brain

Brain food

Starting a decade or so ago, a couple of researchers in the field of nutrition got involved with the AAT/H. This is an interesting example of the usefulness, or in this case the lack of usefulness, of credentials. As far as I know, Michael Crawford and Stephen Cunnane have excellent credentials in the field of nutrition; at the very least they've been connected to good universities and gotten what certainly sound like prestigious positions in their field. But when they walked from their familiar field into the field of human evolution, they stumbled badly.

This is related to the fatty acids DHA (docosahexaenoic acid) and LNA (linolenic acid), often referred to as Omega-3 fatty acids. They are indeed needed for brain growth, but there are a couple of major fallacies promoted in saying that this requirement is evidence for an aquatic past. In regard to these fatty acids, Crawford and Cunnane are trying to do something good, but are apparently seriously ignorant of evolutionary theory. The good thing they want to do is push the addition of DHA into foods, such as milk and eggs, much as we have long added vitamin D to milk. This is useful because many people don't eat the kind of diet that would give them a proper dose of DHA or LNA, as our ancestors' diets would. The push for additional DHA in modern diets is overall a good one, in my opinion, but in trying to tie this laudable goal in with a dubious theory, they do themselves no favors.

The argument, in short, is as follows (and contains a classic logical flaw):

DHA is a requirement for normal human brain development
DHA is abundant in fish
hominids needed to eat fish for normal brain development

The first two statements are true -- definitely true, absolutely no question about it. But the third statement is false. The reason the third statement can be false even though the first two statements are true is that the argument is missing information (Fallacy of Exclusion) which makes it seem as though the only place where enough DHA is present is at the shore. And in fact Crawford at least has explicitly (and quite falsely) claimed that "the only place you can do that is at the seashore". This claim just isn't true.

First, we don't really need loads of DHA, and humans (except for infants) can synthesize the necessary DHA from LNA, which is available in vegetable oils as well as meat sources such as wild game (infants get it from breast milk). The Mayo Clinic, which has always had a strong nutritional slant to their medical practice, says "One tablespoon of vegetable oil easily meets your daily requirements." And people who've calculated the amounts of energy and DHA and/or LNA fatty acids needed to develop normal brains note it's available even in savanna conditions. They also note that these non-seashore environs offer foods which are richer in other required substances, so the notion that the seashore environment was so much easier to collect food at is only true if you concentrate only on a small portion of the dietary needs. Naturally, you shouldn't do that, but AAT/H proponents who use the Crawford and Cunnane argument do just that, and so instead of looking at dietary factors in terms of whether there's enough of all required parts of the diet in a given environment, they look at where there's lots of only one part of the diet.

Data gathered shows, for instance, that the required DHA is available in savanna and other terrestrial environments as well as that the purportedly required shore-based diet is far lower in energy (also required of course) than the terrestrial diet (Loren Cordain, Janette Brand Miller, S Boyd Eaton, and Neil Mann, American Journal of Clinical Nutrition, Vol. 72, No. 6, 1585-1586, December 2000). The problem for a shore or fish-based diet is made worse by the fact that the especially rich sources of DHA in fish are cold water marine fish which are certainly not the type of fish available -- by any reasonably conceivable scenario -- to our ancestors at the time we see increased encephalization (1-2 mya). They were simply not within a thousand miles of them. The fish that were available were -- so to speak -- a different kettle of fish.

They have DHA, certainly, but actual measurements show they are a no better source than such terrestrial sources as brains, which were highly likely to have been scavenged by hominids (along with marrow) by the time we see the first great brain expansion in our ancestors. They, and other shoreside foods, are also very considerably lower in energy than savanna and other terrestrial foods, making the claim that the shore was a much easier place to get the required diet even more unlikely.

Dietary determinism

Another serious problem here is the dietary determinism inherent in this idea. I've described before how environmental determinism, as practiced in the AAT/H, makes the foolish assumption that environment trumps all when it comes to evolution. Dietary determinism does the same, only with diet as the primary selective force. The theory, as promoted, essentially makes the claim that a DHA-rich food source would somehow give a kickstart to our brain growth, and that just doesn't square with the way nutrition works. The fallacy in the idea of the supposed need for an aquatic diet to get larger brains is the same fallacy that people use when they take megadoses of vitamins -- too little isn't good, enough is good, so lots more is better. Being trained in the science of nutrition, both Crawford and Cunnane should know better, even if they don't understand evolutionary forces very well, but they seem not to understand this, since they do make the mistake.

In dietary issues, you essentially always see the same thing: more is not necessarily better. Often it's far worse -- many dietary necessities, such as vitamin A (and phosphorus for that matter) are toxic in too large a dose. Generally you find that deficiencies hinder growth or health, but larger than needed amounts (within a range which varies between individuals) don't create more growth, development, or health, and they often have the opposite effect. This is a common problem, especially perhaps in North America, where we tend to often think that if a little is good, more and more is always better. With most things there's a level that's needed and more does nothing, or nothing good. This is a problem with dietary supplements which always needs to be kept in mind, and is why most dietitians suggest a varied and balanced diet as the best way to obtain good nutrition.

One of their critics sums up the core problem with the Crawford and Cunnane idea: "In this Lamarckian scenario, the quiescent brain appears to be waiting patiently for humans to discover aquatic foods and then, eureka, the brain is free to enlarge and modern humans result. Not only are the selective pressures involved in this scenario unspecified, no information is provided as to how these large-brained humans were then able to provide DHA and other brain-specific nutrients for themselves or their developing offspring once they moved away from lacustrine or shore-based environments." Katharine Milton, pg. 1587 American Journal of Clinical Nutrition, Vol. 72, No. 6, 1586-1588, December 2000

In other words, if you want super-smart monkeys, you're not going to get them by stuffing fish down their throats.

An obvious null hypothesis

One handy tool to use in science is the null hypothesis, which consists of -- to be simplistic -- taking an idea, stating pretty much it as its "opposite", and see if you can make as good a case for the opposite idea. You shouldn't be able to, not if the original idea was accurate. If you can, then you've tested the original idea and found it wanting as an explanation -- but it doesn't mean your alternate, "opposite", explanation is accurate. In fact, if both opposing explanations work equally well, neither one is good on its own -- you may be able to combine them into a new, accurate explanation, or you may need to start over. But what you have done is to test the first idea.

In the case of the idea of seashore DHA being needed for brain growth, there are a couple obvious ways to test the idea with a null hypothesis.

One is to ask, were there (before modern supplements say, that would be before 100 or so years ago) people who developed normal brains in the absence of seashore diets? Yes -- rather obviously, there were. So even without any other testing or knowledge we are able to test the idea and finding it lacking in explanatory power.

(You can apply this question to fish-eating or other shoresides as well; all you have to do is realize there are people who didn't/don't eat sea, lake, or riverside foods who nevertheless had/have normal brains -- that's it, you've shown the "we needed shoreside foods for brain growth" idea to be false.)

A second null hypothesis test is suggested by the comparisons Crawford made in his statements on David Attenborough's spring 2005 BBC Radio 4 show, The Scars of Evolution. I mentioned it on my page which critiques that program, and have other info there on brains and diet, and how you can compare brain sizes in animals of different sizes (using their EQ or "encephalization quotient"). If dietary determinism were a valid way of looking at this problem (as Crawford suggests -- and Attenborough suggests even more explicitly -- on that show) you need to wonder why all creatures which eat fish don't have huge brains. Diving ducks, sea gulls, herons, otters, seals -- why aren't they at least dolphin smart? Mind you, they shouldn't necessarily be, not if you realize that large brains are not always an advantage, as all sensible evolutionary theorists do. But if you're not sensible, use dietary determinism, and imagine that diet trumps all, what about all those not overly bright fish-eating species? Why are the smartest of them, outside of only a few dolphin species, only as large-brained as monkeys and apes which eat mostly fruit and nuts?

It doesn't hurt to do more testing than these two null hypotheses -- for instance the nutritional data people have rounded up concerning the relative value of seashore and other diets vis a vis our evolution is terrific and ultimately useful, or at the very least interesting But this data isn't actually needed to counter the seashore diet and brain growth idea. The real problem here is that this particular idea is so easy to counter, using one or both of the above null hypotheses, that it shouldn't have seen the light of day, at least not in anything like the form it did. It should've been thought through and had things like a null hypothesis applied to it by the original authors of the idea even before they wrote their first drafts of their first papers on it. The problems with it are that basic.

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