This popular snack was thought to cause weight gain — but it actually zaps belly fat

Turns out this myth is nuts.

For decades it’s been widely believed that eating nuts causes weight gain.

Tree nuts in particular have a high calorie and fat content, prompting skepticism as to whether they should be incorporated into a healthy diet.

However, a groundbreaking new study published in Nutrients has uncovered that nuts do not cause people to pile on the pounds — and can actually lead to a loss of abdominal fat.

Scientists from from Vanderbilt University Medical Center looked at 84 millennial-aged adults (22–36 years old) — a demographic that has increasing rates of Metabolic Syndrome (MetSx), a cluster of conditions that increase risk for heart disease and diabetes.

The millennials had at least one MetSx risk factor, such as high blood pressure, high blood glucose, excess body fat around the waist or abnormal blood cholesterol levels.

Participants were fed either one ounce of unsalted mixed tree nuts, such as pistachios, or one ounce of a carbohydrate-based snack, such as unsalted pretzels or graham crackers, twice a day for 16 weeks. They did not make any additional dietary restrictions or changes in lifestyle habits.

“We specifically designed the study to be able to investigate the independent effects of eating tree nuts on body weight by ensuring that the number of calories the participants ate during the 16-week intervention period matched the amount of calories they expended each day, which is one of the overall strengths of the study design and results,” said Heidi J. Silver, PhD, RD, of VUMC, said in a news release.

Researchers found that the group that consumed nuts had significant health benefits, with a 67% decreased risk of MetSx for females and a 42% decreased risk of MetSx for males.

Those in the nut-eating group also saw no change in energy intake or body weight during the 16-week period.

For females, the study found that eating tree nuts led to reduced abdominal fat — which can lead to MetSx, diabetes and heart disease. For males, research showed that eating tree nuts reduced blood insulin levels.

The group that ate tree nuts were also able to turn the fat consumption into energy more efficiently than those who had the carb-based snack — which could be the reason why the group eating nuts didn’t maintain body weight or fat.

“This carefully designed and well-controlled study shows that eating tree nuts, like pistachios, does not have to lead to weight gain and can be an important part of anyone’s self-health care routine in 2024,” Silver explained.

The Dietary Guidelines for Americans claims that more than half of Americans currently do not meet the daily recommendation of five to seven ounces of nuts and seeds per week.

However, the authors noted that further research needs to be conducted on the cardiometabolic response to tree nuts in other subgroups of the population.