Emily Scott Zoo

When the researchers looked back at the original study’s results, they found that those on diets that matched their genetic predisposition lost 2 to 3 times more weight than women on the “wrong” diets. “We were able to explain why some people were successful” and others were not, even though they followed the same diet, said Mindy Dopler Nelson, a nutritional biologist at Stanford and the study’s lead author. The researchers also tested themselves. “It confirmed my suspicion,” Nelson said of her result. “When I eat a lot of carbohydrates, I tend to put on weight.”

Genetic testing was originally aimed at finding risk for diseases such as cancer, diabetes and Alzheimer’s, but Interleukin hopes to expand its use to include lifestyle counseling—determining what type of diet or exercise is best. “Knowing your genotype for low-carb or low-fat diets could help you increase your weight-loss success,” said Dr. Christopher Gardner, an Associate Professor of Medicine at Stanford and a co-author of the study. “It’s not the end of the obesity epidemic, but we need every leg-up we can get.” The new test is available in the market for a price of $149.

However, some scientists aren’t buying into the findings, saying it’s just another test being promoted without enough research to show it really works. “I’m afraid this may be another attempt to lure the public into purchasing genetic tests that provide little value for those struggling with their weight,” said Raymond Rodriguez, director of the National Center of Excellence for Nutritional Genomics at the University of California, Davis. “I have serious reservations with this study and studies like it,” Rodriguez agreed. “The idea that genetic variants in these genes can predict the likelihood for weight loss in such a small population, particularly since the tendency for weight loss is probably more behavioral than genetic, is simply hard to believe.”