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Wednesday, May 13, 2009

Lactose Tolerance Makes You Fat

The European Human Genetics Conference will be held later this month in Vienna. Excited yet? No? Here are some titles of papers to be delivered there:

• Phylogeography of human Y chromosome haplogroup R1b1b2 (R-M269) in Europe.

• The genetic position of Western Brittany (Finistère, France) in the Celtic Y chromosome landscape.

• Mitochondrial Genome Diversity in Tungusic-speaking Populations (Even and Evenki) and Resettlement of Arctic Siberia After the Last Glacial Maximum.

Still not psyched?

Then let me play my trump card.

European Lactase Persistence Allele is Associated With Increase in Body Mass Index

J. A. Kettunen et al.

The global prevalence of obesity, usually indexed by body mass index (BMI) cut-offs, has increased significantly in the recent decades, mainly due to positive energy balance. However, the impact of a selection for specific genes cannot be excluded. Here we have tested the association between BMI and one of the best known genetic variants showing strong selective pressure: the functional variant in the cis-regulatory element of the lactase gene. We tested this variant since it is presumed to provide nutritional advantage in specific physical and cultural environments. We found that the variant responsible for lactase persistence among Europeans was also associated with higher BMI in a Nordic population sample (p = 1.3*10-5) of 15,209 individuals, the size of the effect being close to that of FTO*. We tested the effect of population stratification and concluded that the association was not due to population substructure.

* FTO is a gene that appears to be correlated with obesity.

Let me attempt to translate that.

Europeans tend to have the highest rates of lactase persistence, also known as lactose tolerance, in the world. (Since the majority of white Americans are descendants of European immigrants, most American adults can also drink milk without suffering symptoms.) We know that lactose tolerance is a simple mutation on chromosome 2. And it is a dominant mutation. So the ability to drink milk as an adult will show up unexpectedly but spread through a population because it conveys at least a small advantage in survival and in having more children survive. That helps account for the European dairy culture.

Why does the ability to drink milk convey an advantage? Milk is an excellent food, with high nutrition in a compact and good tasting source. This study goes beyond that to suggest that milk drinkers will be heavier than non-milk drinkers. In olden times, when starvation was a very real possibility, this was an advantage. Today it may lead instead to obesity, or at least greater weight.

You can find an interesting discussion of this abstract led by Razib at the Gene Expression blog.

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