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.
Dietary interventions that increase leucine and/or protein intake did not result in additional measurable improvements during a four-week alternate-day fasting intervention on body composition, sarcopenic, and cardiometabolic outcomes during weight loss in older men.
Key Findings
Results
No significant group-by-time interactions were found for body composition, sarcopenic, or most health outcomes across the three supplementation groups.
Sixty-one older men with BMI ≥ 23.0 kg/m2 were randomized across three calorie-matched supplement groups: Control (C), Leucine (L), and Protein (P)
The intervention lasted 28 days using an alternate-day fasting (ADF) protocol
No significant interactions (p > 0.05) were found for body composition or sarcopenic outcomes
Supplements were consumed as three doses on feeding days and one dose on fasting days
Results
Significant group-by-time interactions were observed for diastolic blood pressure and HDL cholesterol.
HDL cholesterol showed a significant interaction effect (p = 0.013)
These were the only two outcomes among all measured cardiometabolic markers to show significant between-group differences over time
Results
All body composition measures except bone mineral density significantly decreased over the 28-day ADF intervention regardless of supplementation group.
Significant main effects of time (p ≤ 0.05) were observed for reductions in all body composition measures
Bone mineral density did not show a significant change over time (p = 0.274)
Changes in body composition were not significantly different between Control, Leucine, and Protein groups
Results
Systolic blood pressure and multiple lipid profile markers significantly improved over time across all groups.
Significant main effects of time (p ≤ 0.05) were found for systolic blood pressure
Total cholesterol, LDL cholesterol, total/HDL cholesterol ratio, and triglycerides all showed significant reductions over time
These improvements occurred regardless of whether participants received leucine, protein, or control supplementation
Results
All muscle strength and functional sarcopenic outcomes significantly improved over time across all groups.
Significant main effects of time (p ≤ 0.05) were found for improvements in all muscle strength and functional sarcopenic outcomes
Improvements occurred across Control, Leucine, and Protein groups without significant between-group differences
The study targeted older men at risk of sarcopenia, with BMI ≥ 23.0 kg/m2
Methods
The study used body-mass-scaled dosing for leucine and protein supplementation in a randomized controlled design.
Control group received 0.0 g/kg protein and 0.0 g/kg leucine
Leucine group received 0.0 g/kg protein and 0.08 g/kg leucine
Protein group received 0.4 g/kg protein and 0.04 g/kg leucine (noting the protein supplement also contained some leucine)
All groups were calorie-matched
Outcomes included dual-energy X-ray absorptiometry (DXA), sarcopenic metrics, and blood markers including blood pressure, lipid panels, and diabetic profiles
What This Means
This research suggests that adding extra leucine (a key amino acid for muscle building) or protein to the diet of older overweight men during a four-week alternate-day fasting program did not provide additional benefits beyond the fasting alone for body composition, muscle health, or most heart health markers. The study enrolled 61 older men who were overweight or obese and assigned them to one of three groups: a control group receiving no extra protein or leucine, a group receiving leucine supplements scaled to their body weight, and a group receiving protein supplements scaled to their body weight. All groups followed the same alternate-day fasting schedule for 28 days.
Despite the lack of differences between groups, all participants showed meaningful improvements over the four weeks. Everyone lost body mass, improved muscle strength and functional fitness measures, and saw reductions in systolic blood pressure and multiple cholesterol-related markers (total cholesterol, LDL cholesterol, triglycerides, and cholesterol ratios). These benefits occurred regardless of which supplement group participants were in, suggesting that the alternate-day fasting itself was the primary driver of these improvements. The only outcomes where the type of supplement appeared to matter were diastolic blood pressure and HDL ('good') cholesterol, which showed statistically significant differences between groups.
This research suggests that a four-week period may be too short to detect meaningful differences from leucine or protein supplementation during calorie restriction in older men. While leucine and protein are theoretically important for preventing muscle loss during dieting, particularly in older adults who are at risk for sarcopenia (age-related muscle loss), this trial did not find that body-weight-scaled supplementation at these doses provided extra measurable benefits over the fasting protocol alone within this timeframe.
Check Your Own Numbers
Upload your bloodwork. We'll cross-reference your results against this study and 4,700 others.
Pang B, Yang Y, Cheon B. (2026). 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. https://doi.org/10.3390/nu18193255