Leucine Threshold
- Protein metabolism
- Nutrition
- Muscle building
By Mag. Christian Schönbauer, founder of Hardgainer Performance Nutrition®. Training since 1999, started under 50 kg.
The leucine threshold is the amount of leucine per meal at which your muscle protein synthesis (MPS) really kicks in. For a hardgainer (hard gainer), that means planning protein pulses instead of just collecting daily grams. Three meals with enough protein do more than one big one at dinner.
Note
This page gives you context and guardrails, not individual medical or nutrition advice. If you have a medical condition, kidney problems or take medication, please get it checked by a doctor.
What is the leucine threshold? The definition in 20 seconds
Leucine is an essential amino acid and acts as a signal for muscle building. In practice people often work with about 2 to 3 g of leucine per meal. That figure is derived from protein dose studies, not measured directly as a cut-off. The studies see a plateau around 20 g of high-quality protein after training.
- A signal, not the whole build: Leucine starts synthesis. To keep it running, the muscle needs all the essential amino acids. That is why the whole protein counts, not just the leucine.
- Per meal, not per day: Synthesis responds to each individual meal. In one study, evenly distributed protein produced more muscle protein synthesis over 24 hours than the same amount distributed unevenly.
- For hardgainers this means: Do not just count the daily total. Three to five meals that each clear the threshold are the backbone.
The anchors in the system: protein, DIAAS and PDCAAS for protein quality and MPB as the counterpart to synthesis.
What you control and what you don't
How strongly your muscle responds to a meal is not something you set in detail. What you control is amount, source and distribution.
- Amount per meal: Plan at least 25 g of protein from a complete source. The studies see the plateau around 20 g, and the extra gives you room for imprecise portions in real life.
- Source: Whey, dairy, eggs, meat and fish are rich in leucine. Plant sources often have a lower leucine share, so you need larger portions or combinations.
- Distribution: Three to five protein pulses across the day instead of everything at dinner. Breakfast is almost always the meal with the biggest lever.
- Bundle your snacks: Small snacks with 10 g of protein do little for synthesis. In one study, 10 g of whey after training had no measurable extra effect. Combine them into one full portion instead.
- Energy: Without a calorie surplus, even the best protein distribution builds little. The lean surplus sets the direction, the pulses make every meal count.
Leucine content: skyr, quark, Greek yogurt, eggs and plant sources
How much leucine a food delivers comes down to two numbers: how much protein it has and how high the leucine share of that protein is. Measured per gram of protein, milk protein comes in at 9.0 percent leucine and egg at 7.0 percent. Plant proteins range from 5.1 percent for hemp to 13.5 percent for corn.
| Protein source | Leucine in the protein | Protein for 2.5 g leucine | How to work it out |
|---|---|---|---|
| Milk protein: skyr, quark, Greek yogurt, milk | 9.0 % | about 28 g | If the label says 11 g protein per 100 g, that is about 250 g of skyr, quark or Greek yogurt |
| Egg | 7.0 % | about 36 g | Eggs alone need a big portion, combined with dairy it gets easy |
| Hemp protein | 5.1 % | about 49 g | One serving alone barely gets there, mix it with other sources |
Leucine shares measured in commercially available protein isolates. 2.5 g is the middle of the practical 2 to 3 g range, not a measured cut-off. Finished foods differ, the protein figure on the label is your basis.
Gorissen et al., Amino Acids, 2018Practice: the 14-day check
- Day 0, write down where you are: How many meals do you eat on a normal day, and how much protein is in each? The label value is good enough.
- Document daily: Flag every meal under 25 g of protein. Add morning bodyweight and steps as your measure for NEAT. How much your steps burn is shown by the NEAT Calculator.
- Day 14, check the trend: How many meals per day were above the mark? At two out of four, half your meals run below the threshold. Fix the easiest one first, usually breakfast. If your rate of gain is still flat, the problem is calories, not leucine.
The usual finding is not too little protein per day, it is poor distribution.
Common misconceptions
- “The daily total is all that matters.” Synthesis responds per meal. In one study, the same amount of protein spread evenly across three meals produced 25 percent more muscle protein synthesis over 24 hours than the same amount pushed towards dinner.
- “Leucine alone can replace a protein meal.” A small protein dose with added leucine did not keep synthesis elevated after training as long as a full serving of whey. Leucine starts the process, the whole protein carries it.
- “More protein in one meal always does more.” Beyond the plateau, what mainly goes up is the breakdown of surplus amino acids, not synthesis. Spreading beats stacking.
- “It doesn't work with plant protein.” It does, with a bit more planning: larger portions, combinations and consistent food hygiene.
If you want to build, crank the surplus and stop worrying about food quality. Calories are all that counts, the rest sorts itself out.
Calorie level and food quality are two separate dials. A surplus of 150 to 250 kcal per day as our deliberately cautious starting value, four meals above the leucine threshold and a weekly weigh-in make building plannable. Clean bulk and dirty bulk differ mainly in how much control you keep.
Common questions
What is the leucine threshold and why does it matter for hardgainers?
The leucine threshold is the amount of leucine per meal at which muscle protein synthesis really kicks in. In practice people work with about 2 to 3 g, derived from protein dose studies. It matters for hardgainers because synthesis responds per meal. If you only count the daily total and ignore distribution, you leave stimulus on the table.
How much protein per meal do I need to hit the leucine threshold?
The studies see a plateau around 20 g of high-quality protein after training. We plan with at least 25 g per meal from a complete source such as dairy, meat, fish or whey. With eggs and plant sources you tend to need larger portions. Three to five such protein pulses per day are a solid backbone.
Does the leucine threshold work with plant-based protein sources?
Yes, with a bit more planning. Plant sources often have a lower leucine share per gram of protein. Larger portions, combinations and consistent food hygiene still get you over the threshold reliably.
2 more questionsShow less
How much leucine per meal in grams?
In practice people work with about 2 to 3 g of leucine per meal. That figure is derived from protein dose studies, which found a plateau around 20 g of high-quality protein after training. It is not a measured cut-off. With plant sources you need larger portions, because the leucine share is usually lower.
How much leucine is in quark or skyr per 100 g?
Roughly 1 g per 100 g, worked out from about 11 to 12 g of protein and 9 percent leucine in milk protein. A 250 g tub therefore lands around 2.5 g and clears the threshold, a spoonful stirred into porridge does not. Exact values depend on the product, the protein figure on the label is your basis.
From term to practice: your tools
The threshold is a question of amount per meal. These three tools turn it into a plan for your 14-day check.
See all Hardgainer Tools. If you want more out of your numbers, go with Hardgainer Pro.
What the research says
Four papers behind the claims on this page
The leucine threshold is not a switch, it is a dose-response observation. These four papers set the frame.
- Muscle protein synthesis rose with protein dose and was maximally stimulated at 20 g of egg protein, 40 g did not add more. Six young men after intense leg training, tested with 0, 5, 10, 20 and 40 g. From 20 g, leucine oxidation, meaning breakdown, went up. Moore et al., The American Journal of Clinical Nutrition, 2009
- 20 g of whey raised myofibrillar protein synthesis by 49 percent over 0 g, 40 g by 56 percent, and 10 g had no extra effect. 20 g was enough for maximal stimulation. 48 resistance-trained young men of about 80 kg, measured at rest and after training. Above 20 g, mainly amino acid breakdown went up. Witard et al., The American Journal of Clinical Nutrition, 2014
- 6.25 g of whey, topped up with leucine to the level of 25 g of whey, stimulated synthesis just as well as the full serving at first. Three to five hours after training, though, it stayed elevated only with the full whey serving. 24 men, one-legged resistance exercise, comparing three drinks. Churchward-Venne et al., The Journal of Physiology, 2012
- Evenly distributed protein, around 30 g per meal, produced 25 percent more muscle protein synthesis over 24 hours than the same amount pushed towards dinner. 8 healthy adults, 7 days per distribution in a crossover design. The uneven version was roughly 11, 16 and 63 g. Mamerow et al., The Journal of Nutrition, 2014
What the studies do not cover
None of the papers determined an exact leucine amount as a threshold. The 2 to 3 g figure is derived from protein dose studies. The samples are small, and they measured synthesis over hours or days, not muscle growth over months. Hardgainers were not studied as a separate group.
Your takeaway: three to five meals with at least 25 g of protein each from a complete source. Breakfast is almost always the biggest lever.
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Reading & Resources
The terms directly around the leucine threshold and the pillars next to it.
Content here is general practice guidance and does not replace individual medical or nutritional advice.
