Abbreviated as Leu or simply L, leucine is an amino acid found in most proteins. As the human body cannot synthesize leucine, we must obtain it through our diets, making it an essential amino acid. Luckily, many delicious foods contain leucine in varying amounts. Although leucine deficiency is extremely rare in developed countries, it can occur and wreak havoc on the body. So as you develop your diet, whether you’re a bodybuilder interested in increasing your muscle mass or an average Joe hoping to stay in good health, don’t underestimate the many benefits of leucine.
It is burned by the muscles as fuel.
Leucine is the most plentiful branched-chain amino acid (BCAA) in the body. BCAAs are found in high proportions in muscle when compared to other amino acids, and they have a unique purpose. Unlike other amino acids, muscles can burn BCAAs as fuel. Due to this function, your body’s supply of leucine (and other BCAAs) diminishes when you exercise, and you must regularly replenish it through your diet (source).
It stimulates protein synthesis and assists with muscle building.
Like the other two BCAAs, isoleucine and valine, leucine effectively stimulates protein synthesis, including skeletal muscle protein synthesis. It activates complex muscle-building pathways within the body, allowing the body to build more protein and grow more muscle (source). One of these is the mammalian target of rapamycin (mTOR), which manufactures muscle proteins when activated. Leucine plays a critical role in relation to the mTOR, acting as one of the primary activators of the pathway (source). The mTOR is very sensitive to high concentrations of leucine.
This benefit of leucine should excite anyone looking to increase their body’s bulk, because so long as you exercise properly, maintain a diet that supports anabolism, and consume an adequate amount of leucine, your body should grow. This doesn’t just profit bodybuilders either; since all humans lose muscle over time as a part of the aging process, this is one of the many benefits of leucine that helps all people. By helping the body maintain muscle, leucine can prevent frailty and a loss of independence in old age.
It is especially beneficial to older people.
According to a study completed at the University of Texas in Galveston, older individuals (66 years old) benefited from an increase in leucine far more than young individuals (28-30 years old), possibly due to an increase in leucine sensitivity (source). So if you are over age 65 and wish to increase your muscle mass, try to consume a greater amount of leucine, as it could help activate muscle protein synthesis.
It may help people lose weight and fat.
Some studies suggest that leucine can help people lose fat and reduce their weight. For example, researchers at the University of Illinois have conducted studies that demonstrate that high-leucine diets result in greater weight loss and fat loss. They also found that people with diets high in leucine could better preserve their lean body mass and control their glucose level (source).
A study published by the American Diabetes Association also found that doubling the dietary intake of leucine can “significantly reduce” weight gain caused by a high-fat diet, improve hyperglycemia, and improve hypercholesterolemia. It does this by “increasing resting energy expenditure associated with increased UCP3 expression in thermogenic tissues.” The researchers also concluded that leucine supplementation “improves glucose metabolism and reduces diet-induced insulin resistance” (source). Although the study was conducted on mice, it could help us understand the relationship between leucine and the human body, because mice’s DNA organization and gene expression is similar to humans (source).
Finally, research conducted on Mt. Everest found that leucine can help people burn fat but retain muscle tissue when on a restricted diet. Researchers from the University of Utah studied 10 climbers during their ascent of the world’s tallest mountain. Climbers have unique concerns regarding their diets, as the body can shed a significant amount of fat and muscle (especially muscle mass) during arduous climbs. One of the investigators noted that the results of the study could also help non-athletes at lower altitudes lose weight while preserving lean body mass (source).
It works best under metabolic stress.
Finally, keep in mind that the benefits of leucine listed above are more likely to occur when your body is under metabolic stress. For example, aging is a form of metabolic stress, because your metabolism changes as your body grows older. The body also struggles metabolically when obese and suffering from diabetes (source). Thus, a healthy 30-year-old will not reap the same benefits from leucine as an overweight, diabetic 60-year-old.
Leucine in Your Diet
Nutritionists debate the ideal amount of leucine that adults should consume each day, so we cannot provide a definitive number for those wishing to optimize their diet. However, as we mentioned above, leucine deficiencies are extremely rare in the developed world. Although you must obtain leucine through your diet (since your body can’t synthesize it on its own), you don’t need to worry about consuming vast amounts of certain foods in order to fulfill your daily requirements. If you eat a well-balanced diet, you almost certainly consume enough leucine. After all, the amino acid is found in meat, dairy products, eggs, beans, and a variety of other common foods.
All that said, since a diet rich in leucine can prevent muscle loss and boost muscle mass, you may wish to supplement your leucine intake. People who lack leucine tend to lack protein overall and could benefit from a protein supplement. In fact, research shows that leucine is more effective when consumed as a part of a protein-rich diet as opposed to a leucine-only supplement (source).
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