We have an announcement for everyone who is miserably muddling through one of those trendy DNA-matched diets: They don't make any difference.
A nutrition study published in JAMA reveals that low-carbohydrate and low-fat diets appear to work equally well for weight loss, regardless of which of the recently discovered “dietary genotypes” people have.
The randomized investigation (which is important) by Stanford University researchers assigned 609 overweight but otherwise healthy participants to a low-fat or low-carb diet and followed them for 12 months.
Instead of imposing strict food or caloric restrictions, participants were asked to cut down to no more than 20 grams (0.7 ounces) of fat or carbs a day for the first two months. After this, they were told to eat the lowest amount of whichever food group they were limiting that was possible while still feeling full after meals. Throughout the period, all participants were expected to attend 22 nutrition counseling sessions, where they were encouraged to eat mindfully, consume plenty of vegetables, whole grains, minimally processed foods, and to cook at home.
Twelve randomly timed food intake questionnaires showed that most people stuck to the diet recommendations remarkably well, continuing to eat lower daily amounts of their restricted energy type all year. By the study’s endpoint, the average amount of weight loss in both groups was similar, about 5 to 6 kilograms (11 to 13 pounds).
Based on previous findings from his team and others, lead author Dr Christopher Gardner had hypothesized that participants would be more successful if their assigned diet matched their genetic predisposition toward better metabolism of either carbs or fat. A DNA analysis was performed on each participant to see which versions of the metabolic genes PPARG, ADRB2, and FABP2 they carried. Nine combinations of versions, or genotypes, have been linked to improved carbohydrate burning, whereas five combinations appear to make an individual better suited to fat burning.
But contrary to expectations, individuals randomized to a diet favored by their genotype did not lose more weight than those assigned to the mismatched diet. “There was also no DNA/diet interaction for waist circumference, body mass index, or body fat percentage,” the paper states.
“I had this whole rationale for why these three [DNA variants] would have an effect,” said Dr Gardner to Stat News. “But let’s cut to the chase: We didn’t replicate [our previous] study, we didn’t even come close. This didn’t work.”
Gene activity is undoubtedly involved in the process of gaining and losing weight, this study simply shows that these particular predisposing variants (many others have also been identified) are currently unable to lead us toward personalized, magic wand diet plans.
“The most common type of feedback we got from the most successful participants, in both diet groups, was that we had ‘changed their relationship to food,’" Dr Gardner told Examine.