Sunday, December 15, 2013

Epigenetics Can Help Fix Nutrition Science

Aeon recently posted a great essay critiquing the popular 'selfish gene' analogy, exploring new layers of complexity biologists have since uncovered within the process life uses to propagate itself. One of the hottest new concepts has been 'gene expression' or epigenetics. It's basically the insight that not all genes affect their organism in the same way; some heritable changes can occur that aren't caused by changes in DNA sequence. This promising new field muddles the nature/nurture question in a most intellectually-rewarding way.

One of the greatest potential applications of epigenetic thinking is in the field of nutrition science. Explaining exactly why someone's body fat percentage is what it is remains a murky and contentious area, ironic given the global obesity epidemic. Much of the confusion stems from the difficulty in parsing out heritable effects from lifestyle and cultural factors. As an example of the theoretical clarity epigenetics can provide, consider this question that I've long wondered about (and never found a satisfactory answer to).

Most people agree body fat percentage is in part driven by heritability: kids tend to share the body type of their parents, and we all know people who can eat whatever they want and remain skinny. This heritable component likely contributes to the difficulty people experience when trying to change their basic body type in a sustained way.

So here's my question: say you have a heterosexual couple, both with a propensity to fatten, and they've lived much of their lives overweight. If they conceive a kid, odds are the kid would share this propensity. Now consider what might happen if the couple decided to buckle down, lose weight, get in shape, and then conceive a kid. What would happen? The parents' genes certainly haven't changed, so one might expect the kid to still be cursed with a propensity towards accumulating body fat. But it seems strange to imagine, say, parents who've been thin and fit for 10 years having a kid with a propensity to fatten.*

Epigenetic effects can help explain why this scenario seems unlikely: after 10 years of thinness, the parents have probably undergone major biological changes that are somehow 'locked in' and get passed on to their children.

Hopefully researchers will someday be able to understand the exact dynamics of interactions such as this. If we knew definitively, for example, how long parents must sustain weight loss in order to gift a thinness propensity to their children, it would be a tremendous benefit to society. One can easily imagine compassionate parents being strongly incentivized to lose weight and get healthy themselves in order to enable their children to live better lives with greater opportunity.

*admittedly there's some confounding effects here: parents who are able to make big lifestyle shifts like sustained weight loss probably are insane fitness nuts who are likely to influence the behavior of their children

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