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 Center in Durham, North Carolina. Hormonal changes, a more sedentary routine, unhelpful partners and the accumulation of bad habits over time all play a role, she noted.

“We need to be positive and encouraging because it’s possible to tackle this issue,” Politi said.

These strategies can help:

Scrutinize snacks

One major problem is that people seem to increase their snacks, Klein said. Eating an extra candy bar a day will lead to a 24-pound weight gain in three years, so it doesn’t take a big change in energy balance to gain or lose weight, he noted.

“It does require sort of constant vigilance. You always have to be aware of what you’re doing around food,” Klein noted.

He advised taking mini moves like cutting out one snack a day and then progressing from there. Stop eating after a certain time of day, perhaps after 6 p.m. or after dinner, to eliminate snacks before bed.

Watch for bad food influences from your spouse

After being married for a long time, people in middle age may take on the bad food habits of their partners. Perhaps you never ate dessert every day after dinner, but your spouse loves that ritual, so you join in and it becomes your habit.

Studies show we mirror the behavior of the people we eat with, Politi said. One of her patients recently told her, “My husband is the reason why I gain weight. He is a very slender person who eats as much as he wants and doesn’t gain weight. He definitely hasn’t been a good influence on me.”

Think back on your diet when you were eating according to your preferences, not your spouse’s, and return to that routine’s healthier aspects.

Unfortunately, it’s easier to pick up bad habits than good ones, Klein added.

“Our environment is a bad habit environment, so it’s much easier to pick up eating excess food than to eat fewer calories because we’re surrounded by tasty, delicious foods,” he said.

“That’s how that’s how companies make their profit — selling foods that you know you just can’t eat one.”

Recruit your family to help you lose weight

As a corollary to the tip above, don’t be the sole person in the household to eat healthier.

“If you want to lose weight, everyone you live with has to stick with the guidelines as well because it’s very difficult if only one person in the family is sticking with a certain diet plan and no one else is,” Klein said.

Just having a supportive spouse may lead to less weight gain in midlife, a 2018 study found.

Work on improving your sleep

Studies have shown not sleeping well fuels appetite and affects the part of the brain that controls willpower, Politi said.

“So we are more vulnerable to give into candies and treats,” she noted. “When we don’t sleep well, we feel more tired, which might impact physical activity as well.”

Sleep disturbances due to night sweats, mood changes and the effects of menopause contribute to weight gain in midlife women — though menopause itself “does not seem to substantially influence weight gain,” Mayo Clinic researchers noted.

More than a third of women in their 40s and 50s — 35% — get less than seven hours of sleep a day, a 2017 analysis found. Yoga, stress-management and optimal bedroom conditions can help improve sleep.

Eat less and move more

That advice applies to everyone, of course, but when experts say “eat less,” they need to be more precise, Politi said.

“Eat less processed food,” she advised. “I’ve never, never met someone who tells me that they overeat broccoli or quinoa. People overeat chips and ice cream and cookies.”

For a main meal, she recommended filling half of the plate with non-starchy vegetables and adding 3-6 ounces of lean protein like chicken or fish. That leaves less room for starches.

Both Politi and Klein urged people not to overdo the protein intake.

“People in general eat much more protein than they should in this country, and there’s a real hype about eating protein,” Klein noted.

As for moving more, it’s important to expand beyond cardio as people age, so add balance and strength training to the routine, Politi said. She was a fan of HIIT workouts for people who have little time to exercise.

Maintain, maintain, maintain

It’s so much easier to maintain a healthy weight — starting when people are younger — than to try to lose many excess pounds that have accumulated over the years, both experts said.

But it’s still possible for people in midlife and older to slim down — aging doesn’t make weight-loss more challenging, Klein noted, and the health payoff is huge.

“Aging increases your risk for all kinds of diseases… and the risk is also increased by excess body fat, so obesity and aging are a double-edged sword,” he said.

Losing weight “will improve your chances of not getting those diseases and having a better, healthier lifespan.”