As an open diet plan, intermittent fasting is easy to see: Eat what you want, but only during a specific window – usually eight hours a day.
Instead of counting calories or measuring portions, dieters should just focus on the clock, said Courtney Peterson, a nutrition researcher at the University of Alabama at Birmingham.
“You have a simple rule: eat or don’t eat,” Peterson said.
This technique has grown in popularity in recent years and has become a staple of social media. But why eat time-limited, a form of intermittent fasting, really help people shed pounds and improve health?
Here’s what you need to know about the process:
Intermittent fasting is an eating strategy in which people alternate between fasting and eating, defined as going without food for at least 14 hours, according to Peterson.
This could mean changes such as eating on alternate days, eating five days a week and then fasting for two days, or limiting eating to a specific hour each day.
Intermittent fasting, where people cram all of their food into a daily window of 10 hours or less, is the most popular form of intermittent fasting.
Diners will have breakfast until 10am or late afternoon and dinner until 6pm. or 8 hours and abstain from food the rest of the time.
The time-restricted eating theory supports circadian rhythms, or the body’s internal clock. Spending more time fasting can improve body processes that regulate blood sugar and fat metabolism, according to scientists.
Preliminary research in mice from 2012 suggested health benefits from intermittent fasting. Small studies in obese people show that this practice can help reduce obesity and improve other health markers.
Research shows that people on time-restricted diet plans tend to eat more calories, which may explain the weight loss.
Collaborative research shows that obese adults can lose 3% to 5% of their baseline body weight by cutting 200 to 550 calories per day without targeting calories.
But larger studies of people over longer periods of time show that time constraints alone don’t matter. A 2022 study published in the New England Journal of Medicine followed 139 obese people for a year.
Participants either followed a calorie-restricted diet during a specific time window or ate the same amount of calories throughout the day. Both groups lost an average of 14 to 18 pounds—but there was no significant difference between strategies.
“Our data so far show that time-restricted eating is no better or worse than calorie restriction,” Peterson said. This method also does not help you burn more calories.
However, Peterson said the simplicity of the time limit can make it easier than the usual diet. “Almost nobody likes to count calories,” she says.
Early clinical trials with six- to 10-hour eating windows found that time-restricted eating was “generally safe,” the researchers wrote in the journal Obesity.
But the headline study presented this year at the American Heart Association’s Scientific Sessions found that people who eat less than 8 hours a day have a higher risk of dying from cardiovascular disease than those who eat more than 12 to 16 hours a day.
The study, said Dr. Francisco Lopez-Jimenez of the Mayo Clinic, was not published in a peer-reviewed journal.
But he said there is reason to be cautious. Long-standing evidence suggests that skipping breakfast may be associated with cardiovascular disease and death.
People should check with their healthcare provider before attempting a restricted diet, especially if the fast continues into the evening.
“It’s just a call to pause before recommending a special diet,” Lopez-Jimenez said.
