Intermittent fasting maybe not better than counting calories

Jonel Aleccia, MDT/AP Health Writer

As weight-loss plans go, it’s easy to see the allure of intermittent fasting: Eat what you want, but only during certain windows of time — often just eight hours a day. Instead of counting calories or measuring portions, dieters just have to pay attention to the clock, said Courtney Peterson, a nutrition researcher at the University of Alabama at Birmingham. “You have this really simple rule: Eat or don’t eat,” Peterson said.

The technique has skyrocketed in popularity in recent years, becoming a trending topic on social media. But does time-restricted eating, a form of intermittent fasting, really help people shed pounds and boost health?

Intermittent fasting is a meal strategy where people switch between fasting and eating on a regular schedule, defined as at least 14 hours with no food, Peterson said. Variations include eating every other day, eating five days a week and then fasting for two days, or limiting daily eating to certain hours. Time-restricted eating, where people condense all of their eating into a daily window of 10 hours or less, is the most popular form. Diners will delay breakfast until 10 a.m. or noon and then eat dinner by 6 p.m. or 8 p.m., forgoing food the rest of the time.

The theory behind time-restricted eating is that it supports the circadian rhythm, or the body’s internal clock. Spending more time in a fasting state may boost the body’s processes that govern blood sugar and fat metabolism. Early studies in mice starting in 2012 showed health benefits from time-restricted eating. Small studies in people with obesity suggested the practice might 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 weight loss. Results from combined studies suggested that adults with obesity who limited their eating hours without focusing on calories naturally reduced their energy intake by 200 to 550 calories a day, losing 3% to 5% of their baseline body weight. But a larger study of people observed over a longer period showed that the time restrictions alone might not matter.

A 2022 study published in the New England Journal of Medicine tracked 139 people with obesity for a year. Participants either followed a calorie-restricted diet during a certain time window 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 right now suggests that time-restricted eating isn’t any better or worse than cutting calories,” Peterson said. Nor does the technique help burn more calories, she added. Still, Peterson said, the simplicity of time restriction might be easier to maintain than a typical diet. “Almost no one likes calorie counting,” she said.

Early clinical trials with eating windows of six to 10 hours found that time-restricted eating was “generally safe,” researchers reported in the journal Obesity. But headline-grabbing research presented this year at an American Heart Association scientific session suggested that people following an 8-hour time-restricted diet had a much higher risk of death from cardiovascular disease than those who ate over 12 to 16 hours. That research hasn’t been published in a peer-reviewed journal, noted Dr. Francisco Lopez-Jimenez, of the Mayo Clinic. But he said there is reason to be cautious. Longstanding evidence suggests that skipping breakfast may be linked to cardiovascular disease and death.

People should check with their health care providers before they try restricted eating, especially if the fasting window lasts until midday. “It’s a call for pausing before you just recommend a particular diet,” Lopez-Jimenez said.

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