Diet and genes: not so simple

One of the potential benefits of genetics in medicine and public health comes when two interventions are about equally good on average, but with a lot of variation between people.  We can hope that genetics explains which intervention works for which people, and lets us pick the right one for each person. So far, this hasn’t happened.

It didn’t happen again this week, with the results of a randomised trial comparing low-fat and low-carb diets.  A group of basically healthy but overweight or obese adults were randomly allocated to being recommended a low-fat diet or a low-carb diet.  After a year, the average weight loss in each group was about 6kg.

There are some genetic variants that have been found in previous studies to predict the success of low-fat vs low-carb diets.  This trial was set up to look at those genetic variants: even though the low-fat diet wasn’t better overall, was it better in people who were expected to be genetically suited to it? Here’s a graph from the research paper showing the distribution of weight losses in each group:

There’s no sign that genetics is helping.

It’s still plausible that genetic differences contribute, and even that we could use them to choose diets if we knew more. But right now, if you want to know whether you’ll lose weight on a particular (reasonable and moderate) diet, the only way to tell is to try it.