Thirty to 45 minutes of intense exercise. Boom—there’s your answer. If you want to just take that info and (literally) run with it, be our guest. But you strike us as the inquisitive type, so we’ll explain why this length of time and toughness appears to work best for weight loss.

When it comes to dropping pounds, working out can be both a blessing and a curse: Burning more calories than you take in is, of course, the basic recipe for weight loss—and exercise can definitely help with the burning part. But depending on the kind of workout you do, it may also trigger hunger hormones that lead to overeating, or at least to replacing the calories you torched during your sweat session.

There is, however, a sweet spot. Research has found that intense exercise (where you get your heart rate up around 75 percent of your max) affects levels of the hunger hormone ghrelin in a way that actually suppresses your appetite afterward better than less vigorous workouts.

“An acute bout of high-intensity exercise distributes blood away from the stomach and intestines due to the need for greater circulation of blood to the muscles, which may be a factor involved in appetite suppression. This does not occur with less demanding exercise,” explains David Stensel, Ph.D., a professor of exercise metabolism at Loughborough University in Leicestershire, England, who has done numerous studies on the subject. And the effect lasts for several hours—and possibly even days—after your workout.

Duration also is a factor. “If people exercise for longer periods, the suppression of hunger may not be as great,” he adds. So 30 to 45 minutes of running, for example, is better than 60 to 90 minutes of walking, because you’ll expend a lot of energy, but your appetite will be blunted afterward. In fact, a recent study suggests that interval workouts—alternating 30-second all-out bursts of exercise with a minute of recovery—may have a slight edge over sustained vigorous exercise.

Another weight-loss-boosting bonus: “Higher-intensity exercise gives you that ‘afterburner’ effect, where your body continues to burn calories at a faster rate even when you’re not exercising anymore,” says Tony Maloney, a spokesperson for the American College of Sports Medicine and fitness center manager at the National Institute for Fitness and Sport in Indianapolis. Less taxing workouts don’t give you that same post-exercise burn. (Sorry, yoga, we still love you for plenty of other reasons!)

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