What Is Leucine?

A Guide to Leucine Foods and Leucine Supplements

leucine weight loss supplement
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You've probably seen leucine supplements on store shelves at your local vitamin shop or drug store. Product packages often claim that the substance can help you build muscle or lose fat more effectively. But do you really need a leucine supplement to take advantage of these benefits? What if you just eat more leucine foods? Scientific research and expert advice can help guide your decision.

What Is Leucine?

Leucine, or l-leucine, is an essential amino acid. Amino acids are the building blocks of protein. Protein helps your body to build and maintain muscle. An essential amino acid is an amino acid that must be provided in your diet because your body doesn't make it on its own. 

But leucine is special type of essential amino acid called a branched chain amino acid (BCAA). There are three branched chain amino acids: isoleucine, leucine, and valine. These BCAAs stimulate protein synthesis in the muscle. Simply put, they help the body to improve health, boost athletic performance, and combat muscle loss.

How Much Leucine Do I Need?

The USDA and other organizations provide guidelines for your intake of certain nutrients, including protein. For example, according to the 2015-2020 USDA Dietary Guidelines, an adult female should consume about 46 grams of protein (or 10-35 percent of her daily calories). Adult men should consume roughly 56 grams of protein per day.

Other organizations provide recommendations based on weight and activity type. For example, the Academy of Nutrition and Dietetics, Dietitians of Canada, and the American College of Sports Medicine suggest that endurance athletes consume 0.5 to 0.6 grams of protein per pound of body weight each day. Strength-trained athletes should consume 0.7 to 0.8 grams of protein per pound of body weight each day.

But these recommendations don't necessarily break down the protein guidelines into specific recommendations for leucine or other essential amino acids. Some researchers, however, have provided suggestions.

The 10th edition of the Recommended Dietary Allowances lists leucine requirements at just 14 mg/kg/day for adults, but much higher intakes for younger people. However, one widely cited study, recommends that dietary intake of leucine be raised to 45 mg/kg/day for sedentary individuals, and more for those participating in intensive training. Other sources recommend 40 mg/kg body weight/day and many others recommend intakes in that range.

Leucine Foods

If you choose to monitor your leucine consumption to see how your intake compares to recommended guidelines, you may have a hard time getting exact numbers. While total protein is listed on the Nutrition Facts label of the foods you buy, the label does not distinguish how much of that protein is leucine. However, scientists estimate that the leucine content of protein is assumed to vary between 5 and 10 percent.

If you would like to boost your intake, the following are foods high in leucine. Many of them are foods you probably already eat.

Leucine Foods (grams of leucine/100g)

  • Eggs (1.40)
  • Chicken (1.48)
  • Soybeans (2.87)
  • Almonds (1.49)
  • Whey protein powder (10.0-12.0)
  • Soy protein powder (7.5-8.5)
  • Beef (1.76)
  • Salmon (1.62)
  • Peanuts (1.67)
  • Chickpeas (0.63)
  • Lentils (0.65)

Other foods with leucine include milk, corn, brown rice, cheese, chia seeds, octopus, and pork.

Leucine Supplements

If you don't think you are getting enough of this branched chain amino acid, you may be tempted to use a leucine supplement. There are different reasons that people might use one of the popular products. Research regarding leucine supplements has yielded different results based on different goals.

Leucine for Athletic Training

L-leucine supplements are very popular in the bodybuilding and athletic community. Since BCAAs are known to help boost muscle growth, powders and pills are widely sold online and in health food stores. Most leucine supplements provide about three to five grams of leucine per serving. Consumers may choose to more than one serving of the supplement per day.

So are the l-leucine supplements worth it for bodybuilders or strength training athletes? Studies have provided mixed results. For example, in one study of college aged-males, researchers found that supplementing with leucine did not improve strength or skeletal muscle mass during a three month testing period. The researchers did, however, see cell changes in the muscles that may provide benefits if supplementation and training were continued longer.

Another study published in 2017 found that leucine supplementation (three grams per day following training) did not increase strength or muscle mass in healthy young subjects who consumed enough protein overall.

However, other studies have shown that leucine supplements may help boost muscle mass during intense strength training, and research is ongoing to more fully understand how leucine may help athletes in sports such as high altitude climbing.

Leucine for Weight Loss

For several years now, researchers have been studying the impact of leucine on weight loss. Some scientists believe that leucine can help your body hold on to muscle mass when you are dieting. Maintaining muscle mass is important for both initial weight loss and for weight maintenance because those muscles help your body burn more calories every day.

Other scientists believe that leucine may help enhance glucose and insulin homeostasis—a great benefit for dieters who get constant cravings. Authors of one study suggest that BCAAs, and specifically l-leucine, may play a key role in helping dieters to stabilize blood sugar levels and maintain muscle mass. Other researchers have found similar results, suggesting that leucine may play a role in the treatment of obesity and metabolic syndrome.

But research into l-leucine supplements has not been able to show conclusive results that leucine can cause weight loss. In fact, since many leucine supplements are targeted to weightlifters who want to gain weight the products may contain significant calories.

Leucine for Wellness

Consumers may choose to take a leucine supplement simply to improve their health and wellness. If you are concerned that you don't get enough of this vital nutrient, then you may be tempted to buy a supplement. But nutrition experts say that you probably don't need it.

Katherine Brooking MS, RD is the co-founder of AppforHealth.com. She acknowledges that there is some scientific support for leucine supplementation among bodybuilders and even among the elderly who need to maintain muscle mass. But she says that most adults in the US are consuming adequate amounts of leucine in their diets. 

Furthermore, she says that leucine in food is likely more beneficial than leucine in supplements. "Research indicates that that to be effective, leucine should be consumed as part of a protein-based diet rather than simply taken as a supplement in capsules," she says. "Studies on rats that consumed a 40 percent protein diet containing leucine recorded beneficial effects, but different results occurred when leucine was simply dropped into the diet as a supplement without being part of a complete protein. In that situation, the rats’ fat mass increased and muscle gain decreased."

A Word From Verywell

Even though conclusive evidence has evaded researchers, you may still be tempted to take a leucine supplement just in case it might help. But a better option is to increase your intake of leucine foods. If your goal is to lose weight, you should choose leucine foods that are lower in calories and prepare the foods with as little added fat and calories as possible.

You can also make sure that you consume enough protein in your daily diet and incorporate strength training into your workout routine to build and maintain muscle. If you are concerned that you are not getting enough leucine, speak with a registered dietitian or a sports nutritionist to put together a balanced meal plan for improved health, wellness, or athletic performance.

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