Whether you squeeze in exercise during the morning before the day demands your attention, or in evening after you’ve crossed everything off your to-do list, you probably prep with a hearty breakfast or snack to fuel you through your workout.

But if you’re really trying to get in shape for swimsuit seasons, a new study published in the Journal of Physiology shows that the most effective way to slim down is to exercise in a fasted state. That is, break a sweat first thing in the morning and then have breakfast.

If the idea of working out on an empty stomach sounds unsettling to you, consider the results of the study. Researchers divided twenty-eight healthy young men into three groups who all ate the same carbohydrate-heavy, fat-soaked diet for six weeks. The group that didn’t exercise at all, to no one’s surprise, packed on the pounds, stored more fat in their muscles and developed insulin resistance.

Those who consumed a carb-and-fat-heavy breakfast before and after working out strenuously for sixty to ninety minutes — and guzzled carb-spiked sports drinks while sweating — gained about half as much weight as the gluttonous group.

Lastly, the group that exercised before eating a bountiful breakfast in the morning gained almost no weight and did not develop resistance to insulin, a precursor for diabetes.

The fact is, firing up your muscles in a fasted state causes them to burn fat for energy rather than carbohydrates — resulting in a slimmer middle. But the catch, of course, is that your body needs fuel to perform at its max effort. How can you run five miles without at least a banana for sustenance?

The researchers suggest a low-intensity sweat session is better than none — and to work up from there. Burning some calories before breakfast could just help get you a slim beach body by summer.