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A precision nutrition approach to weight loss didn't hold up in a study testing low fat versus low carb depending on dieters' DNA profiles. Previous research has suggested that a person's insulin levels or certain genes could interact with different types of diets to influence weight loss. Stanford University researchers examined this idea with 600 overweight adults who underwent genetic and insulin testing before being randomly assigned to reduce fat or carbohydrate intake. (Tanner, 2/20)

Despite some earlier studies claiming that genetic variants predict whether someone has a better chance of shedding pounds on a low-carbohydrate or a low-fat diet, and despite a growing industry premised on that notion, the most rigorous study so far found no difference in weight loss between overweight people on diets that “matched” their genotype and those on diets that didn’t. The findings make it less likely that genetics might explain why only some people manage to lose weight on a low-carb diet like Atkins and why others succeed with a low-fat one (even though the vast majority of dieters don’t keep off whatever pounds they lose). Unlike cancer treatments, diets can’t be matched to genotype, the new study shows. (Begley, 2/20)

Anyone who has ever been on a diet knows that the standard prescription for weight loss is to reduce the amount of calories you consume. But a new study, published Tuesday in JAMA, may turn that advice on its head. It found that people who cut back on added sugar, refined grains and highly processed foods while concentrating on eating plenty of vegetables and whole foods — without worrying about counting calories or limiting portion sizes — lost significant amounts of weight over the course of a year. (O'Connor, 2/20)