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When Sara Pereda, 35, lost 7 pounds on Weight Watchers in 2007, the New York City woman thought she’d finally achieved a body she could be happy with. Instead, she felt tired and defeated, as she struggled to maintain her weight.

“I would lose a couple of pounds and then would put [them] right back on,” says the 5-foot-4 Pereda.

By April 2015, she was 12 pounds heavier than she’d ever been, weighing 165 pounds and wearing a Size 12 dress. “I even ran a marathon, only to gain weight!” she says.

Pereda, who works in finance, isn’t the only one to have such an experience on Weight Watchers. Her trainer and nutritionist, Ariane Hundt, 40, says she regularly sees people who have struggled with the popular diet, which she claims damages people’s metabolisms, making losing and maintaining weight difficult.

“When clients come in that did Weight Watchers, they usually have a high body-fat percentage and have lost a lot of muscle due to lack of protein, low calorie intake and lack of strength training,” Hundt says. “When you lose muscle, your metabolism slows down. Eating less and being active only works for so long.”

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In 2015, Hundt created a plan targeting clients who have been through Weight Watchers and failed. The $299, four-week program includes 15 boot-camp-style workouts to build muscle and a class on nutrition that advises participants to amp up their protein intake, cut out sugar and take probiotics and other supplements to benefit their digestive systems. Hundt also counsels clients to get plenty of sleep and to avoid exercising too much and eating too little.

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