Not all diets are equal: Time-restricted eating group lost more lean mass
In a subset analysis, loss of lean mass was significantly greater in the time-restricted eating group, compared with the consistent-meals group, in terms of both appendicular lean mass (P = .009) and the appendicular lean mass index (P = .005).
In fact, as much as 65% of the weight lost (1.10 kg of the average 1.70 kg) in the time-restricted eating group consisted of lean mass, while much less was fat mass (0.51 kg).
“The proportion of lean mass loss in this study (approximately 65%) far exceeds the normal range of 20%-30%,” the authors wrote. “In addition, there was a highly significant between-group difference in appendicular lean mass.”
Appendicular lean mass correlates with nutritional and physical status, and its reduction can lead to weakness, disability, and impaired quality of life.
“This serves as a caution for patient populations at risk for sarcopenia because time-restricted eating could exacerbate muscle loss,” the authors asserted.
Furthermore, previous studies suggest that the loss of lean mass in such studies is positively linked with weight regain.
While a limitation of the work is that self-reported measures of energy or macronutrient or protein intake were not obtained, the authors speculated that the role of protein intake could be linked to the greater loss of lean mass.
“Given the loss of appendicular lean mass in participants in the time-restricted eating arm and previous reports of decreased protein consumption from time-restricted eating, it is possible that protein intake was altered by time-restricted eating in this cohort, and this clearly warrants future study,” they wrote.
Dr. Weiss said the findings underscore that not all weight loss in dieting is beneficial.
“Losing 1 kg of lean mass (is not equal) to a kilogram of fat,” he said. “Indeed, if one loses 0.65 kg of lean mass and only 0.35 kg of fat mass, that is an intervention I’d probably pass on.”
Time-restricted eating is popular, perhaps because it’s easy?
Time-restricted eating has gained popularity in recent years.
The approach “is attractive as a weight-loss option in that it does not require tedious and time-consuming methods such as calorie counting or adherence to complicated diets,” the authors noted. “Indeed, we found that self-reported adherence to the time-restricted eating schedule was high; however, in contrast to our hypothesis, there was no greater weight loss with time-restricted eating compared with the consistent meal timing.”
They explain that the 12 p.m. to 8 p.m. window for eating was chosen because they thought people might find it easier culturally to skip breakfast than dinner, the more social meal.
However, an 8 p.m. cutoff is somewhat late given there is some suggestion that fasting several hours before bedtime is most beneficial, Dr. Weiss noted. So it may be worth examining different time windows.
“I am very intrigued about looking at early time-restricted eating – 6 a.m. to 2 p.m.,” for example, he said. “It is on our list.”
Meanwhile, the study results support previous research showing no effect on weight outcomes in relation to skipping breakfast.
The study received funding from the UCSF cardiology division’s Cardiology Innovations Award Program and the National Institute of Diabetes and Digestive and Kidney Diseases, with additional support from the James Peter Read Foundation. Dr. Weiss has reported nonfinancial support from Mocacare and nonfinancial support from iHealth Labs during the conduct of the study. He also is a cofounder and equity stakeholder of Keyto, and owns stock and was formerly on the board of Virta.
A version of this article originally appeared on Medscape.com.