It’s something every fitness guru tells you: exercise boosts your metabolism, increasing your body’s ability to burn fat for hours after your workout is finished. It’s a philosophy that many of us – myself included! – clung to, but a new study found that weight loss resulting from exercise tends to be lower than expected.

This study found that sedentary Westerners actually have the same metabolic rate as the constantly-moving Hadza tribe of hunter-gatherers in Tanzania. In other words, what keeps them fit isn’t exercise, it’s nutrition. They’re lean because they don’t consume the calorific junk food that many Westerners do, not because they’re more physically active than Westerners.

The conclusion of the study is not surprising, says Dr. Timothy Church, who holds the John S. McIlhenny Endowed Chair in Health Wisdom at the Pennington Biomedical Research Center in Louisiana. “It’s been known for some time that, calorie for calorie, it’s easier to lose weight by dieting than by exercise,” he explains. Those who choose low-calorie diets are more likely to stick with their weight loss plan than those who opt for strict exercise regimes.

Diana Thomas, who authored a study with Church, says that most people mistakenly believe that exercise maintains metabolism, or will even speed it up, when the reality is quite different. One study that monitored exercise, food intake, and metabolic rate found that participants’ basal metabolic rates actually dropped as they lost weight, even though they exercised every day. Though they burned up to 500 calories during an exercises session, their total caloric burn each day was lower than it would have been if their metabolism hadn’t changed. As a result, they lost less weight than expected.

Anyone who has attempted to lose weight knows that the mental aspect is half the battle, which makes it twice as hard to pursue your goals when you’re monitoring your calorie intake and exercising regularly, but still not seeing the results you’d hoped for. In an attempt to account for the metabolic dip and create more realistic expectations for weight loss, Thomas has developed a new weight loss calculator that will help health-seekers set more effective goals.

Thomas has been working with a group of volunteers, using her new formula to create improved predictions about how much weight they can expect to lose from exercise. So far, she says her predictions are proving accurate and participants are pleased with the results, though her estimates are for less weight loss than under the old formula. “It’s better to meet lower expectations,” she says, “than to be disappointed that you’re not losing what you supposedly should.”

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