Extra protein or leucine did not spare lean tissue during alternate-day fasting in older men

What the research found

News-Medical reported this on 7 October 2026. 3390/nu18193255, by Pang, Yang, and Cheon. It was a three-arm double-blind randomized trial. Eighty men were recruited and 61 finished, ages 60 to 89, BMI at least 23, from November 2022 to May 2023. The trial excluded smokers, vegetarians and vegans, people with a dairy allergy, diabetes, uncontrolled hypertension, and kidney or liver conditions. For four weeks they used alternate-day fasting. The products were matched for calories and dosed per kilogram. 08 g per kg per serving. 04 g leucine per kg. The control was a chocolate product with neither. Three servings were used on feed days and one on fast days. On a fast day the self-selected meal was at most 600 kcal, between noon and 2 pm. 9 kg lean tissue). Bone mineral density did not change. LDL cholesterol, total cholesterol, the total-to-HDL ratio, and triglycerides improved over time. HDL fell slightly in the protein group. Systolic blood pressure fell. Fasting glucose, insulin, HbA1c, and HOMA-IR did not change. 10 kg per square meter. 92 seconds. 44 kg. 05 m/s. 08. There were no differences between arms. The Montreal Cognitive Assessment rose modestly. Eleven people gained lean tissue while losing weight (5 control, 4 protein, 2 leucine). Adherence was about 93 percent for fast-day meal timing, only 63 percent for staying at or under 600 kcal, and 99 percent of servings. There was no group that kept a daily meal pattern without fast days, so the fasting pattern itself is not proven as the cause. Protein and leucine did not spare lean tissue compared with the control product. This is not advice to fast. It may not apply to women, to frail adults, or to people with sarcopenia. Two participants felt weak or light-headed on day 1. One reported bloating, constipation, and slight joint discomfort. Not medical advice.

Evidence level: Clinical trial. This is among the stronger kinds of evidence, but one study rarely settles a question.

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