Thrifty gene hypothesis

The thrifty gene hypothesis is a hypothesis proposed in 1962 by geneticist James Neel to explain the tendency of certain ethnic groups, such as American Indian (see New World Syndrome), to tend towards obesity and diabetes. It postulates that certain genes in humans have evolved to maximize metabolic efficiency, lipid storage and food searching behaviour, and that in times of abundance these genes predispose their carriers to diseases caused by excess nutritional intake, such as obesity.

In the past, this genotype would have been advantageous for puberty or child-bearing women during periods of famine. However, with the advent of high fat, high carbohydrate, and low fiber diets, and relative inactivity this genotype is no longer advantageous because it is too efficient. This has led to obesity and related health problems.

It follows from the theory that ethnic groups with a history of food scarcity will have undergone a relatively high evolutionary pressure and hence may harbor more thrifty genes than other populations.

It is often cited alongside the thrifty phenotype hypothesis (or Barker hypothesis) as an explanation for progressive prevalence of obesity in the Western world.

The fundamental basis of the thrifty gene hypothesis has recently been challenged in papers by Speakman. who suggests that famines have occurred too infrequently and involve insufficient mortality to favour selection of thrifty genes. He suggests that instead release from predation around 2 million years ago may have allowed the regulation system in humans to drift - generating the pattern we observe today of a distribution of body weights: with some people obese but many others quite thin.