By Lew Kizer — 2026-10-17 — Health & Nutrition
The short answer
A four-week randomized trial published in Nutrients (2026) assigned 80 men aged 60 to 89 to extra protein, extra leucine or a calorie-matched control during alternate-day fasting; 61 completed it. All groups lost about 2.2 kg, including 0.9 kg of lean mass, and the supplements did not prevent lean-mass loss compared with control. The authors suggest resistance training may be needed alongside nutrition.
Key facts
- Nutrients 18(19):3255; covered Oct. 7, 2026.
- 80 men aged 60–89 with BMI 23 or above recruited; 61 completed.
- Groups: protein plus leucine, leucine alone, or calorie-matched chocolate control.
- Average loss: 2.2 kg body mass (1.3 kg fat, 0.9 kg lean mass) across groups.
- Grip strength and walking speed improved slightly, with no differences between groups.
- Short, small study without resistance training or a non-fasting control.
KINGSPORT, Tenn., Oct. 17, 2026 — When older adults lose weight, some of what they lose is muscle. A new trial tested whether extra protein could stop that, and the answer was not what many people expect.
This article reports research and is not medical advice.
The trial
Researchers recruited 80 healthy, community-dwelling men aged 60 to 89 and asked them to follow alternate-day fasting for four weeks, with a fasting-day meal of no more than 600 calories. Each man was randomly assigned to a protein-plus-leucine supplement, a leucine-only supplement, or a calorie-matched chocolate drink. Sixty-one completed the study, published in Nutrients.
What happened
On average the men lost 2.2 kg (about 5 pounds): 1.3 kg of fat and 0.9 kg of lean mass. Grip strength, sit-to-stand time and walking speed improved slightly, and blood pressure and several cholesterol measures improved. None of these changes differed between groups. Eleven men gained lean mass while losing weight, spread across all three groups.
The authors concluded the supplements did not provide extra benefit and suggested resistance training may be needed alongside nutrition.
Limits
The study was small and short, included only relatively healthy men, had no strength-training arm and had no non-fasting comparison group. Only 63% stayed within the fasting-day calorie limit. It does not show that protein is unimportant; it shows protein alone may not be enough over four weeks.
What to take from it
Spread protein across meals, and pair it with strength work your clinician approves. Our meals for seniors and protein-first meals for smaller appetites pages explain how to choose. For adults 65+ on GLP-1 medicines, see our new guide to eating to protect muscle after 65.
Browse this week's high-protein meals.
Commentary, not medical advice
The SmashMeals perspective
Protein still matters, especially when you eat less, whether from fasting, age or a GLP-1 medicine. This trial is a reminder that it is a team effort with your muscles. Eat protein across the day and lift something heavy a few times a week, with your clinician's OK.
Frequently asked questions
Does extra protein protect muscle when older adults lose weight?
In this four-week trial in older men on alternate-day fasting, extra protein or leucine did not prevent lean-mass loss compared with a control drink. Other research suggests protein works best combined with resistance training.
How much protein do the new Dietary Guidelines recommend?
The 2025–2030 Dietary Guidelines recommend 1.2 to 1.6 grams of protein per kilogram of body weight per day, with protein foods at every meal. Your clinician can tailor this, especially if you have kidney disease.
Does this apply to people on GLP-1 medications?
This trial did not study GLP-1 users. Professional guidance for GLP-1 therapy also emphasizes adequate protein plus resistance exercise to help protect lean mass.
Sources and credits
Follow the original sources for context and verification. A reference is not an endorsement of SmashMeals.
- Does extra protein protect aging muscle during fasting? (opens in a new tab)
News-Medical
Why it matters: Detailed summary of the trial design and results.
- Effects of body-mass-scaled protein and leucine supplementation during weight loss in older men (Nutrients) (opens in a new tab)
Nutrients (MDPI)
Why it matters: The peer-reviewed paper.
- New U.S. Dietary Guidelines released (opens in a new tab)
Morrison Foerster
Why it matters: Current federal protein guidance of 1.2–1.6 g/kg/day.