Does the Popular 16:8 Fast Live Up to the Hype?

Does skipping breakfast and squeezing in all your meals between noon and 8 p.m. make losing weight easier? A new study suggests this trendy form of intermittent fasting may not live up to its promises. The number of pounds trimmed by the popular weight loss strategy may be statistically insignificant when compared to structured meals eaten during the course of a full day. Not only that, time-restricted eating may cost you muscle mass. New research published at JAMA Internal Medicine suggests the jury is still out on the benefits.

Time-restricted eating calls for fasting for 12 hours or longer each day. Many fans carry out a daily 16-hour fast by skipping breakfast and eating all their meals before 8 p.m. on what is widely known as the 16:8 diet. Experts suggest better results may come from eating earlier in the day.

Fasters lost only a half-pound more than regular eaters

Scientists conducting the study gathered 116 overweight adults. The participants were divided into a control group, directed to eat three daily meals, and another group instructed to eat all their food within the 16:8 window.

Researchers found the 16:8 participants lost an average of two pounds over three months. That was only a half-pound more than those in a control group.

Lean muscle mass was the source of 65 percent of the fasting group’s weight loss. That’s more than double the rate you’d expect to see in normal weight loss. Participants on the fasting diet ate less protein, which may be one reason for the rate of muscle loss.

Earlier studies have shown that eating a large breakfast, a meager lunch, and an even smaller dinner helps adults lose more than eating a small breakfast and a larger dinner. That strategy also led to greater improvement in cardiovascular risk. Previous studies show that consuming most of the day’s calories after midday is at odds with our biological clocks. Our bodies metabolize food better earlier in the day.

Critics say the study didn’t last long enough

Some critics of the study say the trial period didn’t last long enough for definitive results. A longer study comprised of more participants likely would have found a larger amount of weight lost by the 16:8 group, they said.

A nutritionist who was not involved in the JAMA Internal Medicine paper said a time-restricted strategy is usually the easiest kind of fasting for most people and one of the easiest ways to limit calorie intake. The eight-hour window encourages people to cut between 300 to 500 calories out of their diets, say nutritionists.

“This was a short study, but it was enough of a study that to me it calls into question whether this works—and if it does work, then the magnitude of the benefit is very small,” said the senior author of the study. Dr. Ethan Weiss, a cardiologist at the University of California, San Francisco, said he was surprised by the findings.

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