Don’t Get Left Behind: Why Leucine Matters Most for Plant-Powered Athletes

Leucine and amino acids


Plant-based diets are all the rage these days. Due to concerns about the environment, health, and animal welfare, we’re adding more plant-based foods to our plates. Yet we still need to feed our bodies (and muscles) with high-quality protein to maintain health and sustain muscle strength and mass.

Although protein is only a single macronutrient, it’s one that people who eat a plant-based diet are most likely to fall short of. If you don’t get enough protein in your diet, you won’t get the most out of your strength-training workout and your muscle gains will fall short.

Insufficient dietary protein can even interfere with muscle recovery. And there’s one amino acid, in particular, you should focus on to support muscle growth. It’s a branched chain amino acid called leucine.

Leucine: The Muscle-Building Powerhouse

Why leucine? Leucine is one of twenty amino acid building blocks that goes into making proteins, including the muscle proteins that build muscle tissue. It’s an “essential” amino acid, meaning your body needs it but can’t make it on its own, so you must get leucine from dietary sources. It’s also a branched-chain amino acid, amino acids that are important for muscle growth. The other two branched chain amino acids are isoleucine and valine.

Research shows that leucine is an “anabolic trigger. This means it can stimulate muscle protein synthesis, a process essential for muscle growth and repair. During exercise, your hard-working muscles sustain microscopic damage, and leucine plays a key role in initiating the rebuilding process, so you recover quicker from exercise and build new muscle tissue.

One way leucine works its magic is by activating a critical pathway for muscle growth called the mTOR pathway. By turning on the mTOR pathway, leucine signals the body to increase protein synthesis, facilitating muscle recovery and growth.

The Plant-Based Dilemma

While plant-based diets offer numerous health benefits for your health and the environment, they make it harder to get sufficient leucine. High-quality animal proteins, such as meat, eggs, and dairy, are the best sources of this essential amino acid while plant-based proteins contain lower levels of leucine. Yet, you can still get enough leucine in your diet with careful planning and by adding more plant-based foods that contain this essential amino acid.

Fortunately, there are vegan-friendly options that can help bridge the leucine gap. Some of the best plant-based sources of leucine are firm tofu, navy beans, seeds, peanuts, lentils, spirulina, and oats. Plus, you can also get leucine from peas, rice, and soy plant-protein isolates. That’s why so many vegan and vegetarian athletes supplement their diet with plant-based protein powder and shakes.

Prioritizing Leucine for Optimal Muscle Recovery

It’s controversial, but the timing of when you get leucine may affect your workouts and how much benefit you get from strength training. This idea goes back to the idea of an “anabolic window,” a critical period after a workout when your body is primed to accept nutrients for muscle repair and growth. The idea is that failing to provide your body with adequate leucine during this critical period can hinder the recovery process and limit gains in strength and muscle mass.

Proponents of the anabolic window theory believe you should consume protein, including branched-chain amino acids like leucine within an hour of a workout. Some think we should be even more aggressive and get a dose of protein within 30 minutes of a workout.

However, other research suggests that the anabolic window is longer, up to 6 hours after a workout. How long the anabolic window lasts may depend upon the type of exercise you’re doing, your training status, exercise intensity, and age. Still, it’s a smart idea to consume protein that contains leucine as soon as you can after a workout.

When you work out, your leucine levels drop. One study found that supplementing with leucine at 50 mg/kg body weight/day prevents the decline in leucine that athletes experience with strength and speed training. Other research shows that consuming supplemental leucine spares muscle glycogen and reduces protein breakdown during endurance workouts. It also improves exercise performance.

Strategize Your Meals to Optimize Leucine

Getting enough leucine means you’ll have to plan, especially if you eat a plant-based diet. Specifically, the current recommended daily intake (RDI) for leucine is 17.7 mg per pound of body weight for most adults. But if you’re training hard and trying to maximize muscle growth, you may need more, up to twice this amount.

So, make sure you’re eating a leucine-rich snack after a workout and getting leucine throughout the day. Some of the best plant-based sources of leucine include:

  • Soy protein
  • Beans
  • Lentils
  • Seeds
  • Nuts

If you’re eating an exclusively plant-based diet, you will need a leucine supplement to get enough leucine to support muscle gains.

Keep Your Diet Balanced

While getting enough leucine is important, you’ll get the most benefits if you adopt a balanced approach to health and nutrition. If you eat a plant-based diet, choose foods that will supply you not only with the protein your body needs, but micronutrients and phytonutrients that support your health.

Also, be aware that most people who eat a strict plant-based diet need a B-12 supplement. Consider booking a few sessions with a nutritionist to ensure you’re covering all the nutritional bases if you eat a plant-based diet.

The Bottom Line

Now you know the key role that leucine plays in muscle growth and that you need to get it through diet. More so than any other amino acid, it turns on your muscle growth “machinery” by activating the mTOR pathway. Now the only thing you must do is make sure you’re getting enough. Don’t forget that muscle building is more than strength training, there’s a nutritional component too. Make sure you’re getting it right!


  • Ask the Expert: Leucine and Vegan Athletes – Today’s Dietitian Magazine. Todaysdietitian.com. Published 2022. Accessed April 2, 2024. https://www.todaysdietitian.com/newarchives/JJ22p9.shtml
  • Mero A. Leucine supplementation and intensive training. Sports Med. 1999 Jun;27(6):347-58. doi: 10.2165/00007256-199927060-00001. PMID: 10418071.
  • Waskiw-Ford M, Sarkis Hannaian, Duncan J, et al. Leucine-Enriched Essential Amino Acids Improve Recovery from Post-Exercise Muscle Damage Independent of Increases in Integrated Myofibrillar Protein Synthesis in Young Men. Nutrients. 2020;12(4):1061-1061. doi:https://doi.org/10.3390/nu12041061.
  • Langyan S, Yadava P, Khan FN, Dar ZA, Singh R, Kumar A. Sustaining Protein Nutrition Through Plant-Based Foods. Front Nutr. 2022 Jan 18;8:772573. doi: 10.3389/fnut.2021.772573. PMID: 35118103; PMCID: PMC8804093.
  • Tibor Vellai. How the amino acid leucine activates the key cell-growth regulator mTOR. Nature. 2021;596(7871):192-194. doi:https://doi.org/10.1038/d41586-021-01943-7
  • ‌”Role of Leucine in the Regulation of mTOR by Amino Acids: Revelations ….” 01 Mar. 2001, https://www.sciencedirect.com/science/article/pii/S0022316622147577.

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