Time-restricted eating is a popular form of dieting, but a new study suggests that it is what you eat—rather than when you eat—that is important for weight loss.
Researchers from Johns Hopkins University found that the amount of calories consumed is likely still what leads someone to lose weight, instead of the time that they ate.
However, while fasting may not directly lead to weight loss, it may still be helpful for treating obesity. This is because it can provide a simple way for people to naturally eat fewer calories by watching the clock, rather than watching what they eat.
For the study, the team randomly assigned 41 adults with obesity and prediabetes to one of two groups. The first group followed a time-restricted eating diet, where they could only eat from 8 a.m.-6 p.m. and ate most of their calories in the morning.
The second group stuck to a less time-restricted diet, where they could eat from 8 a.m. to midnight and ate most of their calories in the evening.
Both groups followed the diet plans for 12 weeks. At the beginning of the study, the researchers assessed participants' history and activity level to estimate how many calories they needed as a baseline. The participants all ate the same number of calories daily throughout the study.
By the end of the trial, both groups lost about the same amount of weight and there were no real differences in fasting glucose, waist circumference, blood pressure, or lipid (fat) levels.
Therefore, the researchers suggest, if fasting diets induce weight loss, it is most likely because the individual has eaten fewer calories—rather than the time that they have eaten.
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However, in an accompanying editorial, researchers from the University of Illinois Chicago argue that time-restrictive eating may still be helpful as intermittent fasting can be an easier diet plan for people to follow than simply counting calories.
Time-restricted eating is a type of intermittent fasting that limits your food intake to a certain number of hours each day. During the eating window, patients are not required to count calories or monitor what they are eating.
In 2020, a review of 27 studies published in the medical journal Canadian Family Physician found that intermittent fasting helped people lose up to 13 percent of their body weight.
The five studies that included participants with type 2 diabetes found that fasting intermittently helped to improve their blood glucose levels.
However, more research is needed to understand if time-restricted eating is a sustainable and safe way to lose weight in the long term. Recent research by the Shanghai Jiao Tong University School of Medicine linked intermittent fasting to heart health problems.
The full findings of the new study are published in Annals of Internal Medicine.
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