Starch and human diversity

Human diversity and agricultural biodiversity interact. The variation that exists between and within crops and livestock products in nutritional content is to some extent matched by — and indeed there is evidence that in some cases it has driven — genetic variation between and within the human populations that make use of them. We’ve blogged about this with regard to lactose intolerance and predisposition to iron deficiency. Now comes a study1 linking variation among human populations in the number of copies of the amylase gene with the amount of starch in their diet2

Amylase is an enzyme found in saliva which breaks down starch. A person may have anywhere from 2-15 copies of the gene which codes for the enzyme (it is called AMY1), due to occasional mistakes during egg and sperm formation. The more copies, the more amylase. It turns out that people who don’t have a lot of starch in their diet, such as pastoralists and rainforest hunter-gatherers, tend to have fewer copies of AMY1 than people on high carb diets, such as agricultural communities and hunter-gatherers in arid environments. From the abstract of the paper:

Higher AMY1 copy numbers and protein levels probably improve the digestion of starchy foods and may buffer against the fitness-reducing effects of intestinal disease.

I guess what this means is that as breeders tinker with the nutritional value of the products of crops and livestock, they should keep in mind that people may differ — perhaps significantly — in the extent to which they will be able to benefit from the changes they make. Are current efforts to breed more nutritious crops, by the CGIAR Centres for example, linked to physiological and genetic studies of the human populations that are expected to grow them?

  1. Perry, George H. et al. (2007) Diet and the evolution of human amylase gene copy number variation. Nature Genetics. []
  2. I learned about it via a post in Carl Zimmer’s blog The Loom, in which he also talks about a couple of other cases of multiple copies of a gene building up in a genome. []

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