Men lose more weight on a low-carb diet than women — but why?

A new study from the DIETFITS trial, published in the journal Nature, shows that men lost more weight and reported complying better with a low-carb diet than women. This analysis provides helpful takeaways for clinicians about how attention to gender can affect nutritional counseling.

The DIETFITS trial randomized over 600 people to a “healthy low-carb” diet or a “healthy low-fat” diet. After 12 months, they concluded there was no difference in weight loss between the two groups.

As we detailed in our review, when the study first came out, the low-carb group started at 20 grams of carbs per day, but participants liberalized their carb intake after eight weeks. At the end of the trial, they were eating an average of 132 grams of carbs per day. For comparison, the low-fat group was averaging 212 grams of carbs.

That is hardly a fair representation of a very low-carb diet, which could partially explain the null results for weight loss.

But now, lead investigator Dr. Lucia Aronica and her colleagues from Stanford reveal a significant difference in gender-based outcomes.

She reports that men in the low-carb group lost 6.6 pounds (3 kilos) more than men in the low-fat group, but women showed no difference. Why would this be?

The researchers suggest it was likely because of compliance.

The study authors found that men reported complying with the low-carb diet more closely than women, which they felt explained the weight loss difference.

The apparent difference in adherence may be due to different attitudes toward dietary fat. The researchers discovered that before randomization, “women expressed a significantly greater preference for low-fat foods than the men, which might have made it more difficult for the former to adhere to the higher fat content of the healthy low carb [diet].”

From a scientific standpoint, this trial shows the importance of interpreting studies through the lens of gender rather than simply looking at mixed-gender group averages.

From a practical standpoint, this trial shows us that clinicians may need to spend extra time addressing preconceived beliefs about lower-fat versus higher-fat foods, especially when counseling women.

While science is catching on to gender differences, marketing pros have taken advantage of the difference for decades. As Dr. Aronica stated in her Diet Doctor Podcast interview, it isn’t a coincidence that low-fat yogurts are in pink containers and marketed directly to women.

This targeted marketing towards a specific gender may make clinicians’ jobs more difficult when trying to break through stereotypes about dietary fat. But studies like Dr. Aronica’s show us how important it is to take gender differences toward food into account to improve long-term success with low carb.

Thanks for reading,
Bret Scher MD FACC

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