L-Leucine

An essential amino acid from protein, taken for muscle and strength.

People take it for

Strength and muscle
Getting more from protein
Muscle mass with age
Grip and leg strength
Everyday movement

A plain-English overview, not advice. Written from published reviews and trials and from what people say in public forums.

Compare L-Leucine prices per dose

What is L-Leucine?

Leucine is an essential amino acid, which means the body cannot make it and it has to come from food. It is one of the three branched-chain amino acids, and usually one of the most plentiful amino acids in good-quality protein foods — a 25 gram serving of whey carries around three grams of it. It is sold on its own as a plain unflavoured powder, and also turns up inside protein blends and amino acid formulas. Its reputation rests on one thing: of all the essential amino acids, leucine is the one that sets off the body’s muscle-building signal most strongly.

Why do people take L-Leucine?

Strength and muscle

The thinking. This is the reason leucine sits on a sports nutrition shelf: people who lift buy it hoping the same training turns into a little more muscle and a little more strength. The thinking is that topping up the amino acid that starts the muscle-building signal tilts the daily balance towards building.

What research has found. One trial followed seventy-five untrained young men through twelve weeks of resistance training, giving them either leucine or a matched dummy powder. Everyone gained muscle and strength on the training, and the leucine group’s gains were not distinguishable from the placebo group’s; the men were all eating above the recommended daily amount of protein. Few studies have measured this yet, so there is little to go on either way.

Getting more from protein

The thinking. Protein only starts muscle building once a meal carries enough leucine, and a light meal, a plant protein or a smaller appetite can fall short. So people stir leucine into a shake or a snack, hoping a modest amount of protein does the work of a large one.

What research has found. One pooled analysis and four trials measured how fast muscle protein was being built, using tracers and muscle samples. In older men and women, adding leucine to ordinary meals or a drink raised the rate; in young men, a small whey drink topped up with leucine matched one four times the size. Leucine alone raised the signal less than mixed amino acid blends. Research here is still young: a few studies so far, mostly pointing the same way.

Muscle mass with age

The thinking. Muscle drifts away from middle age onwards, and reviews describe ageing muscle as needing more leucine in a meal before it responds at all. Leucine is bought in the hope of holding on to what is there, often for a parent rather than by the person taking it.

What research has found. Four reviews pooled trials in adults over sixty, most of them already losing muscle. Two found about a kilogram more lean mass in the supplemented groups, with the clearest differences in those furthest along. The other two separated leucine taken alone from leucine given with protein or vitamin D, and put the clearer differences with the combinations. Studies here point in different directions, so this one is still being worked out; the dose, how long people took it and who took part all seem to matter.

Grip and leg strength

The thinking. Strength is what people notice going first: the jar that will not open, the shopping that feels heavier than it did. That is what sends a lot of leucine into older households. Trials measure it directly, with a hand grip meter or a leg press.

What research has found. Two reviews pooled trials in older adults with muscle loss. One, across six trials and about 700 people, found stronger grip and leg strength in the supplemented groups. The larger, across seventeen trials, found no clear difference where leucine was given alone, and about two kilograms more grip strength where it came with vitamin D. The studies disagree, so this is unsettled: dose, duration and who took part all seem to shift the result.

Everyday movement

The thinking. What worries people about ageing muscle is practical: walking speed, getting out of a chair, keeping up on a hill. Trials measure exactly those things, with a short battery of walking, balance and chair-rise tests. Leucine is taken in the hope that it shows up in how the day goes.

What research has found. Two trials measured this. A UK trial gave 145 adults over seventy with muscle loss 2.5 grams of leucine powder three times a day for a year, and found no clear difference in the walking, balance and chair-rise score. A smaller one, in fifty older people in residential care, gave 6 grams a day for thirteen weeks and found faster walking times. Results here go both ways, which usually means the dose, the length of a trial or the group taking part makes the difference.

What does L-Leucine do in the body?

Muscle protein is built up and taken apart all day long, and which of the two is winning decides whether muscle is gained or lost. Leucine acts as the signal that building can start. Reviews describe it switching on a cellular control system called mTOR, and of all the essential amino acids it does this the most strongly, several times over.

Most of the leucine you eat, roughly four-fifths, is simply used as a building block in new protein. The rest is broken down inside muscle into two other compounds, one of them HMB, which is sold as a supplement in its own right. The signal itself is short-lived: a meal lifts muscle building for a while and then muscle stops responding until the next one, and reviews describe that shut-off arriving sooner in older adults and during spells of inactivity. Exercise stretches the window back out.

What do people say about taking L-Leucine?

These are anecdotes people have shared, not evidence.

What people like

All six threads read are weight-training forums, mostly men, so the reports are about gym work rather than ageing or everyday strength.
A few describe it suiting them best when protein is low or they are dieting: staying leaner, holding size while cutting calories.
Two say they noticed muscle fullness through the day or faster visible growth; one reported stronger pumps and vascularity in the first weeks.
A couple like that it is cheap bought loose, and say they prefer it to the pre-mixed amino acid blends.
One cannot taste it at all on food or in a shake, and two found it fine once mixed into something sweet.

Common complaints

Noticing nothing at all is the commonest report: lifts rising at the usual rate, no change they could point to afterwards.
Taste is the other recurring gripe, described as bitter or chalky, unbearable in water and worse again stirred into savoury food.
Two went light-headed and shaky after very large single doses without carbohydrate, one recording a low blood sugar reading; another noticed swings after stopping.
One reported joint soreness after a week on a very high daily amount, stopped, and judged it poor value against ordinary amino blends.
Several say it is hard to tell what it did, because they took it alongside high protein intakes and other supplements.

How people take it

Five grams is the commonest single dose, taken with meals or around training; daily totals ranged from about seven grams to forty.
Most stir it into a protein shake; others sprinkle it on food, or spoon the dry powder and chase it with water.
Several split it across the day rather than taking it in one go, and one says splitting is what stopped the light-headedness.
People who already eat a lot of protein often say they only reach for it when a meal or shake is light.
Most run it for a few weeks or a couple of months and then judge it, rather than keeping it going indefinitely.

Read from these public discussions:

Who's Using Leucine? (T Nation forums, 2008)
Leucine Experiences (T Nation forums, 2009)
L-Leucine: Suggested Daily Limit? (T Nation forums, 2010)
L-leucine Supplementation (T Nation forums, 2006)
Leucine Timing (T Nation forums, 2010)
What kind of legal supps do you use? (MuscleChemistry forums, 2008)

What forms of L-Leucine are there?

Form	What’s different	Per serving, on products we list
L-Leucine	The free amino acid on its own, not bound into a protein or blended with other aminos.	not in our price tables yet

What else is worth knowing about L-Leucine?

Labels give the amount per serving, which may be more than one scoop. Trials ran from about one to six grams a day; a UK trial gave 2.5 grams three times daily for a year.
A 25 gram serving of whey already carries around three grams of leucine, and leucine is usually one of the most plentiful amino acids in protein-rich food, so a supplement adds to what a meal already provides.
Trials described leucine as well tolerated at up to six grams a day, and one found no change in inflammatory markers. One review notes that supplements can cause digestive upset or interact with some medicines, and that the dose that suits best has not been settled.
Most of the research sits in two places: adults over sixty, often already losing muscle and sometimes living in care homes or rehabilitation units, and short trials in young men. Many of the trials that looked favourable gave leucine with whey protein or vitamin D rather than alone.

If you take medication, are pregnant, or have a health condition, check with a pharmacist or GP first.

The research behind this page (20 studies)

How much does L-Leucine cost?

That depends on the form and the pack, so we work out the price of the same dose of every L-Leucine product we can find and rank them.

Compare L-Leucine prices per dose