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This week in Science: paleodiet

Posted By: Labrat
Date: Tuesday, 18 September 2007, at 10:12 a.m.

For those interested not so much by the benefits of the paleodiet on your well being, but by Dr. Cordain's rationale as a whole (i.e. that our bodies are not adapted to our adopted high-starchy diets), a new paper coming out in Nature Genetics may provide one dent to that line of thoughts.
Now that doesn't mean that it's a good idea to suff ourselves with PBJ bagels, but...

Below is the "News & Views" published in Nature (if one is interested by the actual paper, drop me a line at fbiemar[at]berkeley[dot]edu and I'll send the PDF)

Evolutionary genetics: You are what you ate

Sadaf Shadan

It is hard to think of anyone who doesn't like starchy foods such as pasta, chips, rice or bread. But certain populations, for example hunter–gatherers living in the rainforests or near the Arctic circle, have historically existed on a diet rich in protein and low in starch. George Perry and colleagues conclude that such differences in the amount of dietary starch have moulded the human genome over time (G. H. Perry et al. Nature Genet. doi:10.1038/ng2123; 2007).

Dietary shifts — whether driven by the development of stone tools, by controlling fire or by domesticating plants and animals — have had a major role in human evolution. Perry and colleagues specifically looked at the effect of dietary starch on the number of copies of AMY1, the gene that encodes the salivary amylase enzyme, which breaks down starch.

AMY1 is one of the few genes in the human genome that show extensive copy-number variation between individuals. So the authors first looked at whether additional AMY1 copies are functional. They found that extra AMY1 copies do indeed endow the individuals carrying them with the capacity to produce more salivary amylase. The question then was whether the starch content of past diets dictates the present levels of amylase and, thus, AMY1 copy number.

Perry et al. studied two groups: one consisted of four populations with a low-starch diet and the other of three populations from agricultural societies and hunter–gatherers in arid environments, who traditionally eat high-starch food.
Evolutionary geneticsYou are what you ate

Strikingly, twice as many members of the high-starch-diet group had at least six copies of AMY1. This difference could not be explained by geographical factors because both groups contained people of Asian and African origin. Instead, the authors propose that variations in AMY1 copy number are more likely to have been influenced by positive natural selection.

So what is the advantage of having more salivary amylase? Significant digestion of starch occurs during chewing. This is crucial, and probably vital, in people likely to suffer from diarrhoeal diseases. Moreover, after being swallowed, salivary amylase is carried to the stomach and intestines, where it aids other digestive enzymes.

Of the three copies of the AMY1 gene registered in the reference sequence of the human genome, variations in nucleotide sequences are small. This suggests that the duplication of these genes may have occurred relatively recently, possibly even since the evolution of modern humans about 200,000 years ago. So Perry and colleagues' results, and elucidation of copy-number variations in other human genes, could provide insight into our ecological and evolutionary history

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