Looking to try intermittent fasting? There’s an optimal way to do it, researchers say. Here’s how

Prior studies have shown that intermittent fasting can improve heart and metabolic health, as well as improve blood sugar levels. Dr. Joanne Bruno, an endocrinology fellow at NYU Langone Health in New York, wanted to know if the positive effects were due to weight loss that resulted or the fasting itself.

Bruno and colleagues chose 10 individuals with prediabetes—a serious health condition in which individuals have high blood glucose levels, but not high enough to be diagnosed with diabetes itself—and obesity, and divided them into two groups. All participants were provided food with enough calories to maintain their weight. One group was asked to consume 80% of their calories before 1 p.m.—a type of intermittent fasting known as early time-restricted feeding, or eTRF. The other group ate normally, with half their calories consumed before 4 p.m., and half after.

All participants’ weights remained stable, as Bruno’s team predicted. But those who ate the majority of their calories earlier in the day spent more time with their blood glucose levels in the target range. (The American Diabetes Association recommends that blood glucose levels sit at less than 100 when fasting.)

The study suggests that eTRF can improve blood glucose levels, even in those who don’t lose weight, according to a news release on the research, presented Thursday at the Endocrine Society’s annual meeting in Chicago.

What is intermittent fasting?

Intermittent fasting simply limits when, not what, you eat. There are a few ways to do it, according to John Hopkins Medicine:

Daily approach: You’ll limit your eating to six to eight hours each day and fast for the rest. Bruno’s team had participants eat during an early-in-the-day window, but some choose a later one. A January 2023 study found that an earlier fasting window reduced insulin resistance and improved blood pressure when compared to a later window. There wasn’t much of a difference between the two, however, when it came to weight loss.

Weekly approach: You’ll eat regularly five days a week and limit yourself to one 500-to-600-calorie meal a day the other two days.

Some people fast for longer periods—but longer isn’t necessarily better, according to Johns Hopkins. It may actually backfire, encouraging your body to store more fat as it starves, and it could be dangerous to your health.

What can I eat while intermittent fasting?

When you’re fasting, you’ll want to limit intake to water and calorie-free beverages like black coffee and tea.

When you’re not fasting, you can eat what you want. For those looking to lower blood sugar or lose weight, many experts recommend a Mediterranean diet, which is rich with leafy greens, healthy fats, lean proteins, and unrefined carbs like whole grains. It’s hard to go wrong with such foods, they say.