People get excited about their favorite diets. Maybe you do, too. Are you a low-carb champion or a low-fat fan? Which one really is your best diet?

A big study from the Stanford Prevention Research Center assigned 600 people to either a healthy low-fat diet or a healthy low-carb diet. (No junk food allowed in either one.) People followed their assigned diets for a year and then the scientists compared the amount of weight lost by each group. Average weight loss was astonishingly close. Altogether, people in the study lost a total of 6500 pounds.

That might have been expected, since previous studies have shown a wide range of weight loss results within each type of diet plan and not much difference between them. The DIETFITS study (standing for Diet Intervention Examining The Factors Interacting with Treatment Success) planned to see if they could figure out which is the best diet for specific individuals. They looked at a metabolic marker, insulin secretion, and at a set of three genes that have previously been linked to weight. However, neither of these markers predicted who would do better on a low-fat regime and who would thrive on a low-carb approach.

Consequently, scientists have a lot more work to do before they can identify your best diet. But they did discover that emotional and psychological factors are important. People who were very successful at losing weight told the researchers that the study helped them change their relationship to food. Many found that becoming more mindful about their meals made a big difference.

Find out more about the study and what we know about healthy eating.

Christopher Gardner, PhD, holds the Rehnborg Farquhar endowed chair of medicine at Stanford University and is director of nutrition studies at the Stanford Prevention Research Center. The DIETFITS study he led was published in JAMA on February 20, 2018.

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