TLDR

A new 2026 randomized controlled trial followed 66 adults age 65 and older who took a 3 gram leucine enriched essential amino acid supplement every day for six months while participating in one of two exercise programs. The supplement contained 40 percent leucine and 60 percent other essential amino acids.

The surprising result was that neither exercise group significantly increased appendicular skeletal muscle mass. However, walking speed improved substantially in both groups, suggesting that muscle function may improve even when measurable muscle mass does not. Grip strength findings were less consistent.

The study does not prove leucine caused the improvement because both groups received leucine and both exercised. There was no exercise only or placebo group. Still, the results reinforce an important lesson for healthy aging:

Maintaining physical function may matter just as much as adding measurable muscle mass.

Why Muscle Matters More as We Get Older

Muscle loss is one of the major challenges of aging.

As people get older, skeletal muscle mass, strength, and power tend to decline. When those losses become substantial, they can contribute to sarcopenia, a condition associated with frailty, falls, fractures, loss of independence, and increased mortality.

The authors note that reduced muscle strength and size can increase fall risk, while better lower body strength can improve gait, balance, and the ability to perform normal daily activities.

That is why maintaining muscle after age 65 is not simply about looking muscular.

It can affect whether you can:

• Walk comfortably
• Climb stairs
• Get out of a chair
• Carry groceries
• Recover from illness
• Maintain balance
• Remain independent

The question is how to preserve that muscle effectively.

Resistance training is one of the most important tools.

Adequate protein is another.

And within protein, one amino acid has received considerable attention.

What Is Leucine?

Leucine is one of the nine essential amino acids.

Your body cannot make enough leucine on its own, so it must come from food.

Leucine is particularly interesting because it does more than simply provide building material for muscle.

It also acts as a nutritional signal involved in switching on muscle protein synthesis.

In simple terms, leucine helps tell muscle cells:

Amino acids are available. Start building and repairing muscle tissue.

This is one reason high quality protein sources such as whey, dairy, eggs, meat, soy, and other leucine rich foods are often emphasized for maintaining muscle.

The study authors note that previous research has shown leucine enriched essential amino acid supplements can stimulate muscle protein synthesis, although the longer term effect on actual muscle mass remains less certain.

That distinction is important.

Increasing muscle protein synthesis for several hours after taking a supplement does not necessarily guarantee that someone will accumulate a meaningful amount of additional muscle over six months.

This new study tested exactly that.

The Study

Researchers conducted an open label randomized controlled trial at Golden Jubilee Medical Center in Thailand.

They enrolled:

66 adults age 65 and older

Participants were randomly assigned to one of two exercise groups.

Both groups took the same leucine enriched essential amino acid supplement every day.

The main difference between groups was the type of exercise they performed.

After withdrawals and exclusions, the final analysis included:

60 participants

with:

31 in the regular exercise group

and

29 in the resistance training group.

The average age was approximately:

68 years

and roughly:

73 percent of participants were women.

What Supplement Did They Take?

Every participant consumed one daily sachet of a leucine enriched essential amino acid supplement.

Each serving provided:

3 grams of leucine enriched amino acid protein

with:

40 percent leucine

and

60 percent other essential amino acids.

It also provided:

2 grams of carbohydrate

and

10 mg of potassium.

Based on the 40 percent leucine concentration, that equates to approximately:

1.2 grams of leucine per serving

with roughly 1.8 grams coming from other essential amino acids.

Participants used the supplement every day for:

180 days

or approximately six months.

On exercise days, they took it after exercise.

On nonexercise days, they consumed it between meals later in the morning or afternoon.

That Is a Very Small Amount of Protein

This is one of the most interesting aspects of the study.

Participants were not drinking a 25 or 30 gram protein shake.

They were consuming only:

3 grams of essential amino acids

with about:

1.2 grams of leucine.

The authors point to previous research showing that a small leucine rich essential amino acid dose can produce an anabolic response comparable with a much larger whey protein serving under certain experimental conditions.

That could potentially be valuable for older adults.

Older people sometimes struggle to consume large protein servings because of:

• Reduced appetite
• Early fullness
• Smaller meal sizes
• Digestive discomfort

A concentrated essential amino acid supplement requires very little volume.

But the critical question remains:

Does stimulating muscle protein synthesis translate into more muscle over time?

In this study, the answer was no.

What Exercise Did They Do?

The two groups followed different exercise programs.

Regular Exercise Group

Participants were instructed to:

Walk for at least 30 minutes

Five days per week

and perform quadriceps strengthening exercises at the same frequency.

Resistance Training Group

Participants performed five specific exercises:

• Hip raises
• Side lying straight leg raises
• Seated quadriceps strengthening
• Single leg standing
• Marching for 10 minutes

These were also performed approximately five days per week.

It is worth emphasizing that even the so called control group was not sedentary.

They were walking and strengthening their legs regularly.

That becomes very important when we interpret the results.

The Main Question Was Muscle Mass

Researchers measured appendicular skeletal muscle mass index, or ASMI.

This estimates the amount of muscle in the arms and legs relative to height.

At baseline, average ASMI was:

6.54 kg/m² in the regular exercise group

and

6.80 kg/m² in the resistance training group.

After six months, the changes were:

Regular exercise: minus 0.14 kg/m²

Resistance training: plus 0.10 kg/m².

The difference between groups was not statistically significant.

More importantly, neither group experienced a significant increase in muscle mass compared with baseline.

So despite six months of leucine enriched essential amino acids plus regular exercise:

Muscle mass did not significantly increase.

Does That Mean Leucine Did Nothing?

Not necessarily.

Muscle size is only one aspect of physical health.

Someone can improve:

• Neuromuscular coordination
• Movement efficiency
• Balance
• Muscle quality
• Strength
• Walking ability

without experiencing a large change in measurable muscle mass.

That appears to be what happened here.

Walking Speed Improved Dramatically

Both groups showed substantial improvements in gait speed.

They began at approximately:

1.12 meters per second.

After three months:

Regular exercise: 1.39 m/s

Resistance training: 1.35 m/s.

After six months:

Regular exercise: 1.75 m/s

Resistance training: 1.73 m/s.

That represents an improvement of approximately:

0.63 m/s in the regular exercise group

and

0.61 m/s in the resistance training group.

Both changes were statistically significant compared with baseline.

There was, however, no significant difference between the two exercise groups.

The chart on page 5 of the paper makes this especially clear. Both lines rise almost in parallel across the six month study, showing that walking speed improved similarly regardless of which exercise program participants followed.

Why Walking Speed Matters

Walking speed might sound like a relatively simple measurement.

In older adults, it can be extremely informative.

Slower gait speed can be associated with:

• Frailty
• Reduced mobility
• Increased fall risk
• Reduced independence
• Poorer overall health

Improving walking ability can therefore have much more practical significance than simply increasing a body composition number.

The interesting lesson here is that function improved even though muscle mass did not.

That reinforces the idea that successful healthy aging should not be judged by muscle size alone.

Did Resistance Training Work Better Than Walking?

Surprisingly, no.

The researchers originally expected the resistance training group to gain more muscle.

That did not happen.

Both groups improved gait speed by nearly identical amounts.

There was also no meaningful difference between groups for:

• ASMI
• Gait speed
• Dominant grip strength
• Nondominant grip strength

at six months.

But there is an important reason this result may not be as surprising as it first appears.

The regular exercise group was still doing quadriceps strengthening five days per week, in addition to walking.

Both programs therefore trained the lower body.

The researchers acknowledge that this overlap may have reduced the differences between groups.

This Was Not Traditional Heavy Resistance Training

Another detail worth considering is what the study called resistance training.

The program consisted primarily of:

• Hip raises
• Leg raises
• Seated knee extension movements
• Single leg balance
• Marching

Those are useful exercises, particularly for older adults and fall prevention.

But they are not necessarily the kind of progressively overloaded resistance training typically used when the specific goal is maximizing muscle hypertrophy.

There was no indication that participants progressively added substantial external resistance over the six months.

That matters because building muscle usually requires a progressively challenging stimulus.

So the lack of muscle growth does not necessarily mean:

"Resistance training cannot build muscle after 65."

Far from it.

It tells us that this particular exercise program combined with this particular amino acid dose did not significantly increase ASMI.

What Happened to Grip Strength?

Grip strength produced mixed results.

For the nondominant hand, the regular exercise group improved from approximately:

21.77 kg at baseline

to:

24.67 kg after six months.

That improvement was statistically significant.

The resistance training group went from:

23.81 kg

to:

25.86 kg

but the six month change did not reach statistical significance.

For dominant hand strength, neither group maintained a statistically significant improvement at six months.

The page 5 graphs show the same pattern visually. Grip strength moved somewhat upward, but the differences between groups were small and highly variable.

The authors caution that the study was not adequately powered to confidently determine whether leucine supplementation affected grip strength.

So this should be treated as an interesting observation rather than strong evidence.

Why Did Muscle Function Improve Without More Muscle?

There are several possibilities.

Better Neuromuscular Coordination

Repeated exercise can improve how effectively the nervous system recruits existing muscle fibers.

You can therefore become stronger or move more efficiently without necessarily adding substantial muscle tissue.

Better Balance and Movement Skill

Exercises involving single leg standing, walking, marching, and lower body strengthening may improve balance and coordination.

That can translate directly into faster walking.

Muscle Quality May Have Improved

Two people with identical muscle mass can have very different levels of strength and physical function.

Factors such as muscle fiber recruitment, mitochondrial function, fat infiltration, and neuromuscular efficiency influence how well muscle actually performs.

Participants May Already Have Been Relatively Healthy

This is especially important.

These were healthy older adults with relatively good baseline physical function.

Their average Barthel Index was already:

100 out of 100

indicating full independence in basic activities of daily living.

That means there may simply have been less room to improve muscle mass.

Someone with sarcopenia, malnutrition, or lower baseline protein intake might potentially respond differently.

The Study Did Not Actually Test Leucine Against Placebo

This is the biggest limitation when interpreting the headline.

Both groups took leucine.

There was no:

Leucine versus placebo comparison

and no:

Exercise alone group.

So while participants improved walking speed while taking leucine and exercising, we cannot determine how much of that improvement was caused by:

• Leucine
• Exercise
• Their interaction
• Practice effects from repeated testing
• Other factors

The authors themselves emphasize this limitation.

A study designed to isolate leucine would ideally include something like:

Exercise plus leucine

versus

Exercise plus placebo.

That was not done here.

So it would be inaccurate to claim:

"Leucine increased walking speed."

A more scientifically accurate conclusion is:

Walking speed improved during six months of daily leucine enriched essential amino acid supplementation combined with regular exercise.

Why Didn't Leucine Increase Muscle Mass?

There are several possible explanations.

The Participants Were Not Sarcopenic

The intervention may have more impact in people with poor muscle mass or inadequate nutrition.

These participants were relatively healthy.

The Amino Acid Dose Was Small

Three grams of essential amino acids is a very concentrated dose, but it is still a small amount of total substrate compared with consuming 20 to 40 grams of complete protein.

Stimulating muscle protein synthesis requires leucine, but maintaining that process also requires sufficient amounts of all essential amino acids.

Total Daily Protein Was Not Controlled

The study did not tightly control participants' overall diets or daily protein intake.

That makes it difficult to know whether some participants were already consuming plenty of protein while others were not.

Resistance Training Intensity May Have Been Too Low

The exercise program may not have provided enough progressive mechanical overload to produce substantial hypertrophy.

ASMI Measurement Had Limitations

Muscle mass was measured using bioelectrical impedance analysis.

The authors acknowledge that hydration was not controlled, and hydration status can influence BIA estimates.

That could have made subtle changes in muscle mass more difficult to detect.

Leucine Is a Trigger, Not the Entire Construction Crew

One useful way to understand leucine is to think about building a house.

Leucine helps provide the signal to start construction.

But the signal alone does not build the house.

Your body also needs:

• All essential amino acids
• Adequate total protein
• Enough calories
• Resistance training
• Recovery
• Sleep

That is why focusing exclusively on leucine may miss the bigger picture.

A high quality protein source naturally provides leucine along with the other essential amino acids required to actually build new muscle proteins.

The present study used both leucine and other essential amino acids, which is more logical than using leucine alone.

But total nutrition still matters.

How Much Leucine Do Older Adults Need?

This study does not establish an optimal leucine dose.

Participants consumed approximately 1.2 grams of supplemental leucine per day, but that was provided on top of whatever leucine they already consumed from food.

Previous research cited by the authors suggests that low dose leucine rich essential amino acids can acutely stimulate muscle anabolism in older women.

But an acute rise in muscle protein synthesis is different from showing long term increases in muscle mass.

That is exactly what this trial demonstrates.

Six months of supplementation did not significantly increase ASMI.

So we should not interpret 1.2 grams of supplemental leucine as a proven muscle building dose.

Food Still Matters

Leucine is naturally present in high quality protein foods.

Good sources include:

• Whey protein
• Milk
• Greek yogurt
• Cottage cheese
• Eggs
• Meat
• Fish
• Poultry
• Soy foods
• Certain legumes

For healthy older adults, the goal should generally be to first ensure that total daily protein intake is adequate and that meaningful amounts of protein are distributed throughout the day.

A leucine enriched essential amino acid supplement may be especially convenient for someone who struggles to eat enough protein because of poor appetite or early fullness.

But it should not distract from the broader nutritional picture.

Was the Supplement Safe?

Overall, the supplement and exercise programs appeared reasonably well tolerated.

Across all participants, there were no significant changes in:

• Creatinine
• Estimated glomerular filtration rate
• Blood urea nitrogen
• Albumin
• BMI

Kidney function remained statistically stable over the six month intervention.

Two participants did experience adverse events.

One participant developed elevated blood glucose and withdrew.

Another participant with underlying stage 3A chronic kidney disease developed proteinuria and was withdrawn for safety.

The authors report no serious adverse events related to supplementation or exercise overall.

Still, older adults with kidney disease, diabetes, or other significant medical conditions should discuss major changes in protein or amino acid supplementation with an appropriate healthcare professional.

One Important Conflict of Interest

The study was funded by Ajinomoto Co. Thailand, the company associated with the amino acid supplement being studied.

The paper states that the corresponding author did not receive financial support from the company, while the other authors did.

Industry funding does not automatically invalidate a study.

The trial was randomized, and a third party analyst who was blinded to group allocation performed the statistical analysis.

But funding sources are still worth considering, especially because independent replication would strengthen confidence in the conclusions.

Important Study Limitations

There are several major limitations.

First, this was an open label study.

Participants and evaluators could not be fully blinded.

Second, both groups received leucine supplementation, so there was no way to isolate the supplement's independent effect.

Third, both groups performed meaningful lower body exercise.

That probably reduced the researchers' ability to detect differences between the exercise programs.

Fourth, participants were relatively healthy and functional at baseline, so the findings may not apply to people with established sarcopenia or frailty.

Fifth, exercise adherence depended partly on diaries, and 12 percent of the exercise diary data were missing.

Finally, ASMI was assessed using bioelectrical impedance rather than a more precise imaging method such as DXA or MRI, and hydration was not standardized.

These limitations are important because the study's main conclusion is more modest than a headline like "leucine builds muscle after 65" would suggest.

What This Study Really Tells Us

This study is valuable partly because it produced a negative result.

The researchers expected leucine enriched essential amino acids plus resistance training to increase muscle mass.

It did not.

That tells us something important.

Simply adding a leucine supplement does not guarantee measurable muscle growth in healthy older adults.

At the same time, both exercise groups became meaningfully faster walkers.

That suggests maintaining and improving function may not always require large increases in muscle size.

The healthiest approach to aging muscle may therefore involve focusing on multiple goals:

Maintain muscle mass.

Maintain strength.

Maintain walking ability.

Maintain balance.

Maintain independence.

The scale or muscle mass reading is only part of the story.

Simply Good Tip

If your goal is preserving muscle as you age, do not think of leucine as a substitute for protein or resistance training.

Think of it as one part of the muscle protein synthesis signal.

A more complete strategy is to:

• Perform regular resistance exercise
• Eat enough total protein
• Include high quality protein at multiple meals
• Choose protein sources naturally rich in leucine
• Maintain adequate calories and micronutrients
• Stay physically active outside the gym

For older adults who struggle to consume larger protein servings, a small leucine enriched essential amino acid supplement may offer a convenient way to increase essential amino acid availability.

But based on this study, it should not be expected to dramatically increase muscle mass on its own.

The Bottom Line

Can leucine enriched essential amino acids help older adults maintain muscle?

The answer from this study is:

Maybe for function, but not clearly for muscle size.

In this 2026 randomized trial, healthy adults age 65 and older took a daily 3 gram leucine enriched essential amino acid supplement containing approximately 1.2 grams of leucine while following either regular walking and strengthening exercises or a specific resistance exercise program for six months.

Neither group significantly increased appendicular skeletal muscle mass.

However, both groups experienced large improvements in walking speed.

Grip strength improvements were inconsistent and did not clearly favor one exercise program.

The researchers concluded that six months of leucine enriched essential amino acids combined with exercise did not increase muscle mass, while functional improvements in gait speed were observed regardless of exercise regimen.

The bigger lesson is one that applies to healthy aging in general:

Muscle health is about more than muscle size.

Being able to walk faster, move confidently, maintain balance, preserve strength, and remain independent may ultimately matter much more than whether a body composition test shows an extra pound of muscle.

Leucine may play a role in supporting that process.

But resistance exercise, adequate total protein, overall diet quality, and consistent physical activity remain the foundation.

References

1. Thavonlun C, Limsapjaroen J, Yoosuk P, Mahaisavariya C. Effect of leucine enriched essential amino acid supplementation combined with different exercise regimen on appendicular skeletal muscle mass and muscle performance in older adults: an open label randomized controlled trial. JBMR Plus. 2026;10(5):ziag052.
2. Bukhari SS, Phillips BE, Wilkinson DJ, et al. Intake of low dose leucine rich essential amino acids stimulates muscle anabolism equivalently to bolus whey protein in older women at rest and after exercise. American Journal of Physiology Endocrinology and Metabolism. 2015;308:E1056 to E1065.
3. Wilkinson DJ, Bukhari SSI, Phillips BE, et al. Effects of leucine enriched essential amino acid and whey protein bolus dosing upon skeletal muscle protein synthesis at rest and after exercise in older women. Clinical Nutrition. 2018;37:2011 to 2021.
4. Mori H, Tokuda Y. Effect of whey protein supplementation after resistance exercise on muscle mass and physical function of healthy older women: a randomized controlled trial. Geriatrics & Gerontology International. 2018;18:1398 to 1404.
5. Kim HK, Suzuki T, Saito K, et al. Effects of exercise and amino acid supplementation on body composition and physical function in community dwelling elderly Japanese sarcopenic women: a randomized controlled trial. Journal of the American Geriatrics Society. 2012;60:16 to 23.
6. Hurst C, Robinson SM, Witham MD, et al. Resistance exercise as a treatment for sarcopenia: prescription and delivery. Age and Ageing. 2022;51:afac003.

Frequently Asked Questions

Does leucine build muscle in older adults?

Leucine can stimulate signaling involved in muscle protein synthesis, but this six month trial did not find a significant increase in appendicular skeletal muscle mass despite daily leucine enriched essential amino acid supplementation and exercise.

How much leucine did participants take?

Each daily supplement contained 3 grams of leucine enriched essential amino acids, with 40 percent coming from leucine. That equals approximately 1.2 grams of supplemental leucine per day.

Did leucine improve walking speed?

Walking speed improved significantly in both groups, but because everyone received leucine and exercised, the trial cannot establish that leucine itself caused the improvement.

Did resistance training outperform walking?

Not in this trial. The resistance exercise group did not significantly outperform the regular walking and strengthening group for muscle mass, gait speed, or grip strength. Both programs included lower body strengthening, which may have reduced the difference between them.

Is leucine better than whey protein?

This study did not compare leucine enriched amino acids directly with whey protein. Previous short term studies cited by the authors suggest small leucine rich essential amino acid doses can stimulate muscle protein synthesis similarly to larger whey servings in some settings, but that does not mean their long term effects on muscle mass are identical.

What is more important for muscle after age 65, leucine or protein?

This paper cannot answer that directly. Its findings support viewing leucine as one component of a broader strategy that includes sufficient total protein and regular exercise rather than as a replacement for either.