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• Posted August 21, 2026

Diet Quality Versus Cutting Calories: What Matters More For Weight Loss?

Is weight loss really just about calories in, calories out — or does diet quality make a difference?

A team led by Dr. Thomas Keyserling, a professor of medicine at the University of North Carolina at Chapel Hill, followed 360 adults with obesity for two years.

Half were assigned to a Mediterranean-style program that emphasized healthy fats, whole grains, fruits and vegetables, while limiting refined carbs and processed foods.

The other half used WeightWatchers, which focused primarily on cutting calories, while encouraging more fruits and veggies.

After two years, both groups lost about 4% of their body weight. But the Mediterranean-style group made significantly greater improvements in diet quality.

"My key takeaway was the profound impact of the Mediterranean diet on improving our overall eating habits in a way that's sustainable," said Emily Case, a registered dietitian at Northwell Health in New York.

Case wasn't part of the study but says the Mediterranean diet provides a "clear blueprint for food choices that are healthy and nutritious."

"These directly address the underlying causes of chronic disease, diabetes and heart disease by giving you more healthy fats, whole foods and fewer unhealthy carbs, which are key for reducing these things," she added.

Researchers said more investigation is needed to understand how diet quality affects obesity-related health outcomes.

In the meantime, they said these findings suggest weight-loss programs should put greater emphasis on diet quality.

The study was published Aug. 20 in JAMA Network Open.

More information

The American Heart Association has more on the Mediterranean diet.

SOURCE: HealthDay TV, Aug. 21, 2026