A cup of white rice has about 200 calories—not insignificant, considering it’s most often used as a small part of a larger dish. But there’s an easy, natural way to make rice less caloric: add a little fat, then let it cool. According to research presented at the American Chemical Society’s national meeting, using coconut oil and a refrigerator can slash calories by as much as 60%.

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Rice is made up of digestible starch and a special type of carbohydrate called resistant starch, which recent research suggests may be key for weight control. Humans don’t have the enzymes to digest resistant starch, so it isn’t transformed into sugar and absorbed quickly in the bloodstream like digestible starch. Instead, it bypasses the small intestine and is metabolized in the colon, where it’s fermented into short-chain fatty acids that feed healthy colonies of gut bacteria. The more resistant starch a food has, the fewer calories from that starch our bodies will absorb. Resistant starch is plentiful in foods like legumes, beans, whole grains, uncooked potatoes and unripe bananas.

Researchers from the College of Chemical Sciences in Sri Lanka wanted to figure out if they could convert some of rice’s digestible starch into the non-digestible type, and thereby make it less caloric. By testing out 38 different kinds of rice and simulating human digestion in a test tube, they devised a recipe for the least caloric way to cook rice: drop a teaspoon of coconut oil into boiling water, then add half a cup of non-fortified white rice and cook it for about 40 minutes. After cooking, stick it in the fridge for 12 hours.

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Rice cooked this way had at least 10 times the resistant starch as normally prepared rice and 10-15% fewer calories. But researchers think that with certain kinds of rice, the method could cut calories by 50-60%.

Here’s how it works: the glucose units in hot cooked rice have a loose structure, but when it cools down, the molecules rearrange themselves into very tight bonds that are more resistant to digestion, says Pushaparaja Thavarajah, PhD, who supervised the study. Scientists already know that it works in potatoes, but in the new study, researchers thought that adding a fat like coconut oil could add extra protection. It seemed to. The fat molecule wedges its way into the rice, Thavarajah says, and provides a barrier against quick digestion.

Making rice starch more resistant has other perks besides cutting calories. It’ll also feed your good bacteria. “The resistant starch is a very good substrate, or energy source, for the bacteria inside the human gut,” says Thavarajah.

Best of all, the researchers found that reheating the rice didn’t change the levels of resistant starch—so the calorie hack is safe for leftovers, too.

Read next: 4 Ways to Eat More and Still Lose Weight

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Write to Mandy Oaklander at mandy.oaklander@time.com.