A story about why people get fat may be just that

The mismatch between the modern Western lifestyle and the human body reveals itself with every new statistic about rising U.S. obesity rates. Still, gaining a deeper understanding of the biology behind that mismatch has not been straightforward. Sure, more calories in and less exercise tend to make people fat. But explaining how a propensity for obesity evolved and where exactly it’s written in the human genome has been more difficult.

By far the most popular idea of the last 50 years, as contributing correspondent Laura Beil discusses in “Ancient famine-fighting genes can’t explain obesity,” has been the thrifty gene hypothesis. It posits that frequent bouts of famine acted as a force of natural selection among our ancestors, giving an advantage to those whose bodies stored excess calories as fat. The idea makes intuitive sense, but surprisingly little evidence exists to back it up, Beil reports. Efforts to find the genes responsible for this evolutionary edge have largely come up short. That has many researchers in the field embracing a wider palette of explanations. Hopefully, new insights into what primes the body to hold on to calories, and puts many at risk of obesity and diabetes, will soon emerge.

What Beil’s article doesn’t delve into is advice on how to eat, and whether a protein-rich, low-carbohydrate “Stone Age” diet will help you lose weight and stay healthy, a contested claim made in a number of diet books. Whatever the evolutionary story behind the obesity epidemic, the latest salvo in the diet debate appeared this month in the Annals of Internal Medicine. Tulane University researchers and colleagues show that a low-carb diet was better at promoting weight loss and improving cardiovascular risks than was a low-fat diet (go Paleo!). Including genetics in similar studies of diet might allow scientists to map the variation among people and lead to a more complete picture of how evolution has shaped metabolism.

Evolution also acts on disease, as is evident in the update on the Ebola outbreak (see “Experimental drugs and vaccines poised to take on Ebola” and “Ebola genome clarifies origins of West African outbreak,” in this issue). Read about a plan to fast-track experimental therapies and a genetic report that traces the current epidemic’s origins to a single person. In “Long before Columbus, seals brought tuberculosis to South America,” you’ll find another disease detective story, this one fingering marine mammals for bringing tuberculosis to the Americas a thousand years ago.

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