If you'd like to keep your muscles healthy as you age, you'll want to get familiar with leucine (or l-leucine) — especially if you're on a plant-based, vegetarian or vegan diet.
Leucine is a powerful essential amino acid known for maintaining muscle mass. To achieve a well-rounded diet, make sure you're getting enough in your diet so you can enjoy the benefits of l-leucine.
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What Is L-Leucine?
Protein is made up of amino acids and each source of protein has a unique amino acid profile.
So what is leucine good for and what does is it do for your body? Amino acids play different roles in the body, primarily related to making proteins, per the U.S. National Library of Medicine.
As is the case with all essential amino acids, leucine cannot be produced by the body and must be obtained from food. While leucine is present in some plant-based foods (more on that below), it is generally higher in quantity and easier to find in food sourced from animals, per the NIH. That's why plant-based diet followers should pay extra attention to their leucine intake.
Leucine Health Benefits
This essential amino acid plays a number of important roles in your health. Here are the top leucine health benefits you should know about.
1. Improved Muscle Mass
Research on leucine's effect on body composition in healthy young and middle-aged adults is mixed, but there are more consistently positive findings in research among older adults — particularly those predisposed to sarcopenia, the loss of muscle tissue with age.
For example, leucine supplement benefits included positive effects on body weight, body mass index and muscle mass in older people prone to sarcopenia, per an April 2015 meta-analysis in the Journal of Nutrition, Health, and Aging.
Another benefit of l-leucine: Research consistently supports leucine's role in recovery from injury. For instance, supplementing suboptimal protein intake with leucine may be a feasible and effective way to offset anabolic resistance, which can lead to declines in skeletal muscle mass, per an August 2020 review in Nutrients.
That said, there is no reliable research that shows taking supplements of amino acids like leucine can boost athletic performance or help exercise recovery in the average person, per the University of Rochester Medical Center. Always talk to your doctor before starting new supplements.
2. Regulated Blood Sugar
This essential amino acid can also help regulate blood sugar, per the University of Rochester Medical Center. In fact, when leucine was ingested with glucose, it reduced the blood glucose response and strongly stimulated extra insulin production, per a small December 2008 study in Metabolism.
Leucine plays a key role in blood glucose regulation through its effects on pancreatic β cells, liver, muscle and body fat, per a May 2010 review in Nutrition Reviews.
Of course, that doesn't mean popping a leucine supplement will necessarily keep your blood sugar balanced. One of the best ways to keep your blood sugar in check is by eating a varied diet with healthy carbohydrates, fiber-rich foods and good fats (polyunsaturated or monounsaturated fats), per the Mayo Clinic. If you're concerned about your blood sugar or have diabetes, talk to your doctor about a healthy eating plan for you.
3. Human Growth Hormone Production
Leucine may increase the production of human growth hormone (HGH), per the University of Rochester Medical Center.
HGH fuels childhood growth and also preserves your tissues and organs throughout life, according to the Mayo Clinic. But by middle age, your pituitary gland reduces the amount of growth hormone it produces.
That's why synthetic HGH gets a lot of hype: Some people think it can stave off age-related changes like bone loss, but you should be skeptical unless your doctor prescribes it for a specific condition like growth hormone deficiency, per the Mayo Clinic. There is little evidence that HGH can give healthy adults more youth or vitality.
You should aim to include leucine as a part of a nutritious diet to support your overall health, but don't expect a leucine supplement to give you the fountain of youth.
Does Leucine Increase Testosterone?
There is not enough evidence to show that it does in a way that makes an impact on muscle recovery. Testosterone levels increased 24 hours after two daily doses of 3 grams of leucine, but it didn't improve recovery from resistance exercise in young adults, per a small March 2021 study in the International Journal of Exercise Science.
4. Weight Loss
Human studies on leucine for weight loss are limited. That said, some research shows that leucine plays a role in critical metabolic processes — and as noted before, it may help stabilize levels of blood glucose.
L-leucine could potentially be used for weight management or weight loss programs, per an older January 2003 review in The Journal of Nutrition. In fact, dietary levels of leucine might influence muscle mass maintenance during weight loss. However, there's no established leucine dosage for weight loss.
It also doesn't necessarily mean you should go stock up on a leucine supplement for weight loss or expect leucine to burn fat for you. Fad diets and supplements typically don't work long-term for weight loss. Instead, opt for an ongoing lifestyle that includes healthy eating habits, physical activity and realistic goals, per the U.S. Centers for Disease Control and Prevention.
Leucine Side Effects and Risks
You may experience leucine side effects with a supplement, which is one reason it's typically best to get your nutrients from whole foods.
According to the University of Rochester Medical Center, taking leucine supplements can have a number of unwanted effects:
- Negative nitrogen balance: A single amino acid supplement may cause you to have a negative nitrogen balance, which can lessen how well your metabolism works and cause your kidneys to have to work harder.
- Hypoglycemia: Very high doses of leucine may cause low blood sugar.
- Pellagra: Very high doses of leucine can also cause pellagra, symptoms of which include hair loss, gastrointestinal problems and skin lesions.
In general, supplements should not replace healthy, complete meals and it's important to eat a variety of foods, per the U.S. Food & Drug Administration. Combining supplements, using supplements with medicines or taking too many supplements can cause harmful results.
Your health care professional can help you decide if you need leucine supplements and guide you in striking a healthy balance between the foods and nutrients you need.
How to Get More Leucine in Your Diet
Leucine is most commonly found in animal foods such as beef, poultry, fish, cheese, eggs and milk, but it's also present in plant-based foods in smaller amounts.
Of course, you should always aim to achieve a well-balanced diet rather than focus on just one nutrient — so make sure the leucine-rich foods you choose are part of an overall nutritious eating pattern.
Men on a vegan diet had statistically significant lower levels of leucine in their blood, while vegetarians had similar (but still lower) levels of leucine compared to meat-eaters, per a September 2016 study in the European Journal of Clinical Nutrition. This suggests that leucine in the vegetarians' bloodstreams was likely from milk products, which are high in leucine.
If you're on a vegetarian or vegan diet, be sure to get enough protein from plant-based sources and regularly eat soybeans and soy-based products as well as legumes to obtain all of the essential amino acids including leucine, per the Academy of Nutrition and Dietetics.
The recommended daily intake (RDI) for leucine is 17.7 milligrams per pound of body weight.
What Is Fermented L-Leucine?
Fermented L-leucine is made from a vegan leucine food source and processed by fermentation, per Sunland Nutrition. If you're interested in taking supplements, always speak to your doctor first.
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- MyFoodData: "Top 10 Foods Highest in Leucine"
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- Nutrients: "Rehabilitation Nutrition for Injury Recovery of Athletes: The Role of Macronutrient Intake"
- International Journal of Exercise Science: "Leucine Supplementation Does Not Improve Muscle Recovery from Resistance Exercise in Young Adults: A Randomized, Double-Blinded, Crossover Study"
- Nutrition: "Long-term leucine supplementation reduces fat mass gain without changing body protein status of aging rats"
- The Journal of Nutrition: "The Role of Leucine in Weight Loss Diets and Glucose Homeostasis"
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- European Journal of Clinical Nutrition: "Plasma concentrations and intakes of amino acids in male meat-eaters, fish-eaters, vegetarians and vegans: a cross-sectional analysis in the EPIC-Oxford cohort"
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- MyFoodData: "Roasted Chicken Leg"
- MyFoodData: "Skirt Steak"
- MyFoodData: "Pork Chops (With Fat)"
- MyFoodData: "Canned White Tuna (Oil Packed)"
- MyFoodData: "Lowfat Ricotta"
- MyFoodData: "Firm Tofu"
- MyFoodData: "Canned Navy Beans"
- MyFoodData: "Skim Milk"
- MyFoodData: "Roasted Squash And Pumpkin Seeds (Unsalted)"
- MyFoodData: "Hard Boiled Eggs"
- Metabolism: "Leucine, when ingested with glucose, synergistically stimulates insulin secretion and lowers blood glucose"
- Nutrition Reviews: "Leucine metabolism in regulation of insulin secretion from pancreatic beta cells"
- Mayo Clinic: "Diabetes diet: Create your healthy-eating plan"
- Mayo Clinic: "Human growth hormone (HGH): Does it slow aging?"
- U.S. Food and Drug Administration: “FDA 101: Dietary Supplements”