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Ask the RD

QUESTION: Now that I have results from my DNA test, can I use them to figure out which weight loss diet would work best for me?

ANSWER: Few people succeed at losing weight and keeping it off for the long term. Because maintaining weight loss is difficult and complicated, it’s tempting to think our genes can provide a shortcut to predicting weight loss success or failure. After all, genes influence how we metabolize fat, carbohydrate and protein. Some research (Qi et al. 2011) supports the idea that gene variations may help us determine who will lose more weight on a low-fat diet versus a low-carbohydrate diet.

After a small study showed that women matched to either a low-carb or a low-fat diet based on their genes lost more weight than those who were not matched, researchers at Stanford University designed the DIETFITS study (Gardner et al. 2018). This larger study assigned more than 600 overweight adults to either a healthy low-carb or a healthy low-fat diet for 12 months. Throughout the study, participants attended classes led by dietitians, and compliance with assigned diets was good. All participants were encouraged to eat lots of vegetables; focus on nutrient-dense, minimally processed foods; cook at home as often as possible; and minimize intake of added sugars, refined flour and trans fats. They were not prescribed a calorie target.

After 12 months, weight loss averaged 12 pounds for both diet groups. There was zero difference in weight loss for people projected to succeed better on either a low-fat or a low-carb diet based on their genes.

It is disappointing, but unfortunately, we can’t use genes to prescribe a weight loss diet. In the meantime, we do know that improving diet quality—by being more mindful about hunger and satiety cues, increasing vegetable intake and eating nutrient-dense, minimally processed foods—always improves health.

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