Mary The Trieu does hourlong workouts at a CrossFit gym three to five days a week. She is also 5-foot-3 and weighs 205 pounds.

Ms. Trieu avoids junk food and eats balanced meals, but she’s not on a diet. She works out to keep her weight stable and because she enjoys it.

“As I started exercising, I just got this adrenaline rush,” says Ms. Trieu, an admissions officer at Columbia Business School. “It feels good to sweat. And it’s hard. Part of it is my ego: ‘Yes! I’m a bigger person, but I can still do the exercises you’re doing.’ ”

A recent study underscores that there are significant health benefits to overweight and obese people being physically active, even if they don’t lose a pound. The study, of 334,000 Europeans over 12 years, recorded twice as many deaths due to a lack of physical activity as due to obesity.

The study, published in the American Journal of Clinical Nutrition, backs up earlier research about the value of exercise in improving health. It found that as little as a brisk, daily 20-minute walk can extend life expectancy.

Some doctors say the diet industry and popular culture overemphasize weight loss and underemphasize the benefits of exercise for people of any size. Health clubs and fitness studios advertise with images of lean bodies. Many people stop exercising if they’re not losing weight.

Recently, images on Twitter and Instagram of women of all shapes doing yoga have surged, alongside hashtags such as #sizedoesntmatter. Online discussions abound about the best shoes for heavier runners. Plus-size model Ashley Graham will be featured in an ad for retailer swimsuitsforall in Sports Illustrated’s Swimsuit Issue this month. She also stars in a new series of online workouts called Curvy Fit Club.

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