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Debating low-fat vs low-carb diets? New study found a draw

A comparison of diets for weight loss for those with different levels of insulin and metabolic genes did not find a clear winner.

How do genetics and insulin levels affect weight loss? That’s the question a team led by Stanford’s Christopher Gardner, PhD, recently sought to understand. Their research, which appears in the journal JAMA, focused on whether insulin levels and genes related to metabolism affect how people lose weight — and whether their bodies would favor a low-carbohydrate diet or a low-fat diet.

Gardner, who is featured in the video below, explained the motivations for the work in a Stanford Medicine release:

We’ve all heard stories of a friend who went on one diet — it worked great — and then another friend tried the same diet, and it didn’t work at all... It’s because we’re all very different, and we’re just starting to understand the reasons for this diversity. Maybe we shouldn’t be asking what’s the best diet, but what’s the best diet for whom?

For the study, the researchers worked with 609 overweight participants and assigned half to a low-carb diet and half to a low-fat diet. Gardner and his collaborators told all the study participants to eat healthy foods. For example, he counseled that vegetables and salads were a must — and although red meats are low carb, they shouldn't dominate breakfast, lunch, and dinner.

My release details their work:

Over the 12-month period, researchers tracked the progress of participants, logging information about weight, body composition, baseline insulin levels and how many grams of fat or carbohydrate they consumed daily. By the end of the study, individuals in the two groups had lost, on average, 13 pounds. There was still, however, immense weight loss variability among them; some dropped upward of 60 pounds, while others gained more than 20. But, contrary to indications from past studies, Gardner found no link between genotype, baseline insulin levels and a propensity to succeed on either diet.

Although the study didn't find that either insulin levels or genes related to carbohydrate and fat metabolism affected the success of the diets, Gardner said those factors, overall, may still play a role. It just means there's even more data to consider when working to determine what diet is best for a particular individual.

Gardner said he plans to continue analyzing the data collected during this study to learn more. “I’m hoping that we can come up with signatures of sorts,” he told me. “I feel like we owe it to Americans to be smarter than to just say ‘eat less.’ I still think there is an opportunity to discover some personalization to it — now we just need to work on tying the pieces together.”

Photo by RitaE

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