The Thrifty Gene Hypothesis Has Been Thoroughly Refuted
The thrifty gene hypothesis is an intriguing idea developed by geneticist James Neel in 1962 to explain why people get fat. The theory is that homo sapiens evolved through times of famine; in order to survive, therefore, we developed a "thrifty" gene to help us store up excess calories as fat during times of abundance, so that we could burn that fat for fuel during the next famine.
In our modern environment, we can access a tremendous amount of food -- a super supply of calories. Since we didn't evolve to be able to "deal with" this oversupply -- supermarkets and convenience stores at every corner, for instance -- our bodies store too much fat and obesity emerges in the population. The thrifty gene theory allows pro-Caloric Balance Hypothesis researchers to explain why only some of us get fat and not all of us. It also explains why it's "so hard" to lose weight.
It's a neat idea, and it certainly jives with how most of us think about overweight.
So why did Neel and others reject the thrifty gene hypothesis?
1. Gary Taubes does a wonderful job of walking through the various arguments against the thrifty gene in his book Good Calories, Bad Calories (see pages 242-251). To summarize a few points:
a. Obesity seems to confer a serious evolutionary disadvantage, so why would we "evolve in" a mechanism that would make us obese?
b. Evidence suggests that diabetes is a relatively new disease; this suggests that the hypothesis is wrong, since diabetes and obesity closely correlate.
c. The hypothesis rests on the assumption that we evolved through many periods of famine. Ample anthropological evidence contradicts this assumption. Our hunter gatherer ancestors most likely lived in an equilibrium with their environment.
d. In general, when species encounter an overabundant food supply, they multiply -- they don't get fat and sick.
e. One of the main studies often used to defend the hypothesis, a study on Israeli sand rats, could easily be interpreted as providing evidence against the hypothesis and in support of the idea that carbohydrates make us fat.
f. Offer animals like lions and monkeys unlimited calories of meat and protein, and they will eat to satiation and not gain weight. Conversely, provide these animals an abundance of carbohydrate calories, and they will get fat and sick. Again, carbohydrates seem to be the problem, not some strange and as of yet unidentified genetic storage mechanism.
Taubes also makes this argument, which seems exceptionally hard to refute:
"The storage of fat, it seems clear, like all evolutionary adaptations, tends to be exquisitely well suited to the environment -- both internal and external -- in a way that maximizes benefits while minimizing risks."
Okay, so clearly Taubes doesn't believe in this hypothesis. But what do others say? Have "mainstream" scientists had any luck identifying our supposed thrifty gene?
2. Consider this article from abc.net.au:
"Thirty years ago geneticists came up with the 'thrifty gene' hypothesis -- the idea that high rates of diabetes and obesity in indigenous populations could be explained by genes specific to these groups. A study just released by Australian and American researchers dispels the thrifty gene hypothesis."
3. Here's another paper that also rips to shreds any hopes that the hypothesis will work:
"Although it remains a useful stimulus for research, the thrifty gene hypothesis remains a theoretical construct that so far lacks any concrete examples."
4. Here's another article: "Is the thrifty genotype hypothesis supported by evidence based on confirmed type 2 diabetes and obesity-susceptibility variants?"
The authors used an array of tests to search for such a gene. In the results section, they tell us:
"We found no evidence for significant differences for the derived/ancestral allele test. None of the studied loci showed strong evidence... There are no consistent patterns of selection that provide conclusive confirmation of the thrifty gene hypothesis."
Obviously, these papers don't foreswear the possibility that a thrifty gene could be discovered. But if you're trying to explain the obesity epidemic in the simplest possible terms, should you really be invoking a hypothesis from nearly fifty years ago that's been rejected by the person who thought it up and that has countless strikes against it (the arguments laid out by Taubes are but a small number of the possible fusillades that can hurled against the theory)?
Sounds like pretty weak science.
But if the thrifty gene hypothesis cannot be used -- if it doesn't work -- that robs defenders of the Caloric Balance Hypothesis of crucial support.