Losing weight as you age can cost muscle along with fat, so protein and leucine supplements are a common add-on. In a 28-day randomized trial of 61 older men on alternate-day fasting, adding body-mass-scaled protein or leucine did not produce measurable extra gains in body composition, muscle strength or blood markers.[1] The takeaway is to be skeptical of the quick supplement fix, not to ignore muscle.
What the researchers did
Sixty-one older men with a BMI of 23.0 or higher followed 28 days of alternate-day fasting. They were randomly assigned to one of three calorie-matched supplements: a control with no added protein or leucine, a leucine group (0.08 g of leucine per kg of body weight), or a protein group (0.4 g of protein and 0.04 g of leucine per kg). Leucine is the amino acid that most strongly switches on muscle protein building. Doses were scaled to each man’s body weight, taken three times on eating days and once on fasting days.[1]
The team measured body composition with DEXA scans, along with muscle strength and function, blood pressure, cholesterol and diabetes-related markers.[1]
What they found
- The three groups did not differ meaningfully, apart from diastolic blood pressure and HDL cholesterol.[1]
- Across all groups, body composition measures (bone density excepted), systolic blood pressure, total and LDL cholesterol and triglycerides went down over the four weeks.[1]
- Muscle strength and functional measures improved in all groups, including the control.[1]
The authors concluded that dietary changes that raise leucine or protein intake alone gave no extra measurable benefit over this four-week period.[1]
What this study does not show
Four weeks is short, and the participants were men only, so the results may not carry over to women or to longer diets. The control group still got calories matched to the others, so the trial tested the added protein and leucine, not protein in general. It also doesn’t say what happens on other eating patterns.[1]
What to do with this
- Before buying a protein or leucine product to protect muscle, ask your clinician or a dietitian what daily protein target fits your weight, kidneys and medications.
- Track strength, not just the scale. Whether you can still do your usual lifts, stairs and carries tells you more about muscle than weight alone.
- If a plan promises that a supplement will spare your muscle on a fast, look for a randomized trial first. This one found no added benefit.
References
[1] Pang BWJ, Yang Y, Cheon BK. Effects of Body-Mass-Scaled Protein and Leucine Supplementation on Body Composition and Cardiometabolic Blood Markers During Weight Loss in Older Men: A Randomized Controlled Trial. Nutrients, 2026;18(19):3255. Population: 61 older men (BMI 23.0 kg/m2 or higher) on 28 days of alternate-day fasting, randomized to control, leucine or protein supplements. DOI: https://doi.org/10.3390/nu18193255. Finding as used: no significant group-by-time interactions except diastolic blood pressure (p = 0.016) and HDL cholesterol (p = 0.013); body composition, systolic blood pressure and lipids fell and strength and function improved over time in all groups; added leucine or protein gave no additional measurable benefit over four weeks. ↑︎
Kurt Greiner
Kurt is a digital strategist and IT professional blending emerging technology with practical application to help businesses and individuals streamline their digital presence. His current work focuses on the intersection of intentional living and technological resilience, exploring how individuals can leverage modern tools to navigate the second half of life with purpose.
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