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Those extra pounds people start to accumulate in their 40s and 50s are often blamed on a slowing metabolism that burns fewer calories as the body ages.

Enter a new study that found metabolism in adulthood doesn’t slow as commonly believed, seemingly taking away that explanation.

“I was definitely surprised,” said NBC News medical contributor Dr. Natalie Azar.

“But it’s also great news because it actually means maybe we have more control over our weight destiny than we previously thought.”

If it’s not a sluggish metabolism, why do so many people gain weight in midlife? It’s complicated, with factors such as diet, exercise, sleep and even where someone lives factoring into the equation, Azar noted. Many drugs people take as they get older can slow down metabolic rate.

Some experts believe the study has been misunderstood. The findings showed the rate of metabolism doesn’t change per unit of fat-free mass from age 20 to age 60, but the amount of that tissue declines as a person gets older, said Dr. Samuel Klein, director of the Center for Human Nutrition at Washington University School of Medicine in St. Louis.

“So it’s very likely that metabolic rate is decreasing with age,” Klein, who also heads the school’s weight management program, told TODAY.

“But the biggest factor is food intake because it doesn’t take very much to gain weight.”

It’s very common for people to gain weight as they get older, said Elisabetta Politi, a dietitian at Duke Lifestyle and Weight Management