has been sold as a way to lose weight without counting anything, on the idea that the window itself does metabolic work. Most of the supporting trials were short and did not control intake. So 139 patients with obesity were randomized for twelve months to an eight-hour eating window plus , or to the same calorie restriction with no window at all. Did the clock add anything?
The window added nothing measurable. Mean weight loss at twelve months was 8.0 kilograms in the time-restriction group and 6.3 kilograms with daily calorie restriction alone, a of 1.8 kilograms that was not statistically significant. Waist circumference, body-mass index, body fat, lean mass, blood pressure and all gave the same answer. Adverse events did not differ either.
Time-restricted eating asks you to watch the clock instead of the calories, and the claim behind it is that the window itself confers a metabolic benefit. The long-term efficacy and safety of the approach were not clear, partly because the earlier trials were short and partly because a shortened window tends to reduce intake, which muddles cause and effect.
So this trial controlled the calories in both arms. One hundred thirty-nine patients with obesity were randomly assigned to eat only between eight in the morning and four in the afternoon, alongside calorie restriction, or to daily calorie restriction alone. For twelve months everyone followed a diet of 1500 to 1800 kcal per day for men and 1200 to 1500 for women. The primary outcome was the between-group difference in weight change.
Of the 139 randomized, 118 completed the twelve-month visit. Mean weight loss from baseline was 8.0 kilograms in the time-restriction group and 6.3 kilograms in the calorie-restriction group. The net difference of 1.8 kilograms was not statistically significant, with a confidence interval from -4.0 to 0.4 kilograms and a P value of 0.11.
Everything else agreed with the primary outcome. Waist circumference, body-mass index, body fat, lean mass, blood pressure and metabolic risk factors showed no meaningful separation, and adverse events were similar. The conclusion is narrow and useful: among patients with obesity, time-restricted eating was not more beneficial than daily calorie restriction. Note that both groups did lose weight, that one specific window was tested, and that a non-significant 1.8 kilograms is not the same as zero.
wat. Both groups lost weight over a year, and squeezing the eating into eight hours added a kilogram and a half that the statistics would not credit.
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Both groups lost real weight, so the finding is about attribution rather than failure. What produced the loss was the calorie restriction, and the eating window was an extra rule that bought nothing.
How do we know?
Liu and colleagues randomized 139 patients with obesity to eating only between 8 a.m. and 4 p.m. with calorie restriction or to calorie restriction alone, both on 1500 to 1800 kcal daily for men and 1200 to 1500 for women, for twelve months.
What is still unknown
This tests one window, 8 a.m. to 4 p.m., against matched calorie restriction, and 118 of 139 participants finished. A non-significant net difference of 1.8 kilograms does not exclude a small benefit, and the trial was not designed to find one.
Learn something?
Where to next
Does a calorie label on nuts tell you what you absorb?calories