Is intermittent fasting better than counting calories? What to know.

As weight loss plans move forward, it’s easy to see the allure of intermittent fasting: Eat whatever you want, but only during certain periods of time—usually just eight hours a day.

Instead of counting calories or measuring portions, dieters just need to pay attention to the clock, said Courtney Peterson, a nutrition researcher at the University of Alabama at Birmingham.

“You have a very simple rule: eat or don’t eat,” Peterson said.

The technique’s popularity has soared in recent years, becoming a top trending topic on the social networks.

But does time-restricted eating, a form of intermittent fasting, really help people lose weight and improve their health?

Here’s what you need to know about the practice:

Intermittent fasting is an eating strategy in which people alternate between fasting and regular eating, defined as at least 14 hours without eating, Peterson said. This could mean variations such as eating every other day, eating five days a week and then fasting for two days, or limiting daily eating to certain times.

Time-restricted eating, where people condense all of their eating into a daily window of 10 hours or less, is the most popular form of intermittent fasting. Diners will delay breakfast until 10am or noon and then eat dinner until 6pm or 8pm, forgoing food the rest of the time.

The theory behind time-restricted eating is that it supports the circadian rhythm, or body’s internal clock. Spending more time fasting can boost the body’s processes that govern blood sugar and fat metabolism, for example, scientists say.

Early studies in rats, beginning in 2012, appeared to show health benefits from time-restricted eating. Small studies in people with obesity have suggested that the practice may help them lose weight and improve other health markers.

Research has shown that people on time-restricted eating plans tend to eat fewer calories, which could explain the weight loss.

Results from combined studies suggested that obese adults who limited eating hours without focusing on calories naturally reduced their energy intake by 200 to 550 calories per day, losing 3% to 5% of baseline body weight.

But a larger study of people observed over a longer period of time showed that time constraints alone may not matter.

A 2022 study published in New England Journal of Medicine followed 139 people with obesity for one year. Participants either followed a calorie-restricted diet for a set period of time or ate the same number of calories throughout the day. Both groups lost weight – 14 to 18 pounds on average – but there was no significant difference between the strategies.

“Our data now suggests that time-restricted eating is neither better nor worse than cutting calories,” Peterson said. The technique also doesn’t help you burn more calories, she added.

Still, Peterson said, the simplicity of the time restriction may be easier to maintain than a typical diet.

“Almost no one likes counting calories,” she said.

Early clinical trials with six- to 10-hour eating windows found that time-restricted eating was “generally safe,” researchers reported in Obesity magazine.

But research that made headlines presented this year at an American Heart Association scientific session suggested that people who followed an 8-hour time-restricted diet had a much higher risk of death from cardiovascular disease than those who ate for more than 12 to 16 hours.

This research has not been published in a peer-reviewed journal, noted Dr. Francisco Lopez-Jimenez of the Mayo Clinic.

But he said there are reasons to be cautious. Long-standing evidence suggests that skipping breakfast may be linked to cardiovascular diseases and death. People should consult their doctors before trying to restrict eating, especially if the fasting window lasts until noon.

“It’s a call to pause before just recommending a specific diet,” Lopez-Jimenez said.

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