Weighing in

Researchers have found that, contrary to previous studies, insulin levels and a specific genotype pattern don’t predict weight-loss success.

Illustration of a plate and two forks. Riki Blanco illustration

Wondering whether a low-carb or low-fat diet is better for losing weight? A recent Stanford study suggests that people, on average, lose about same amount of weight on either one. The study also notes that you can’t predict the answer by looking at insulin levels or certain gene sequences that affect carbohydrate or fat metabolism.

Related story and video

Read more and watch a video of Christopher Gardner talking about his research.

The study, published Feb. 20 in JAMA, zeroed in on genetics and insulin to discover whether these factors encourage an individual’s body to favor one over the other.

Christopher Gardner, PhD, professor of medicine and the lead author, launched the study with 609 adults between the ages of 18 and 50, though only 481 finished. About half were men and half were women. All of them had their genome sequenced so scientists could look for patterns associated with producing proteins that modify carbohydrate or fat metabolism. They also took baseline insulin tests to measure output.

By the end of the yearlong study, weight loss averaged 13 pounds per person — some lost up to 60 pounds and some gained close to 15 or 20 — and Gardner found no associations between the genotype patterns or baseline insulin levels and a propensity to succeed on either diet.

Still, the study did change habits. “On both sides, we heard from people who had lost the most weight that we had helped them change their relationship to food, and that now they were more thoughtful about how they ate,” says Gardner.