Low-fat or low-carb: can genes or insulin say which is right for you?

We tackled this breakout study in a recent blog post, Low-fat vs. low-carb? Major study concludes: it doesn’t matter for weight loss. If you have already read this, we go into even greater detail in this Study Deep Dives analysis (aka we went Full Nerd) and include previously unreleased Study Deep Dives exclusive Q&As with the lead author — Dr. Christopher Gardner. We also have an extended FAQ section where we tackle many common questions and misconceptions about the study. We also found a blog post from a man who recounted his experiences during this one-year trial (definitely worth a read), a Vox article interviewing four other participants, and a podcast interview with Dr. Gardner himself. Now, onto the analysis!

In free-living, long-term trials (longer or equal to 12 months), multiple studies^[1] have found that low-fat diets^[2] and low-carbohydrate diets^[3] result in small weight loss differences, when compared head-to-head. But there is one central limitation with many of these trials: adherence to the dietary intervention. Many participants start off strong in their assigned low-fat or low-carb diet, but by the end of the study, they have often returned to their usual pre-study eating habits^[4].

Even though these studies report minimal between-group differences, individual weight changes within either dietary group^[4] can be wildly different^[5]: some participants losing 25.0 kilograms (55 pounds) while others gaining 5.0 kilograms (11 pounds).These results suggest that some diets may work better for certain individuals than for others. The reasons for these individual responses are not well understood. Emerging data indicate that insulin sensitivity^[6] or select genetic markers^[7] might help predict a person's success or failure on differing dietary interventions. The present study was designed to identify and investigate potential interactions between diet × genotype and diet × insulin secretion from participants who were actually adhering to their assigned diet.

Many long-term studies comparing low-fat and low-carb trials have yielded minimal between-group weight loss differences. However, individual weight changes within either group can vary tremendously. The study under review was designed to test whether select genetic markers or insulin production could predict weight loss success in participants assigned to either a low-fat or low-carb diet._