Get Your Personalized Supplement StackSupplement Stack Quiz

Leucine

Also known as: L-Leucine, BCAAs, Leucic acid

Overview

Leucine is a branched-chain amino acid (BCAA) and potent nutrient-based signal to activate protein synthesis. Leucine, along with isoleucine and valine, is one of the three branched-chain amino acids (BCAAs). Out of all the amino acids, leucine is the most potent activator of protein synthesis. Cells are able to sense leucine levels, and in response turn on protein synthesis via the enzyme protein mammalian target of rapamycin (mTOR), a master-regulator of protein synthesis. Given the well-established protein-synthesis activating properties of leucine, a number of human trials have been conducted to determine whether adding supplemental leucine to various protein sources can augment muscle protein synthesis (MPS), particularly in older adults. Anabolic resistance is a well-established phenomenon during aging, with cells becoming more resistant to turning on protein synthesis. This can be partly ameliorated with extra leucine, as research indicates that older adults need twice as much leucine compared to younger adults for similar activation of MPS. This increased leucine requirement for MPS in older adults can be partially explained by increased retention of orally ingested leucine in the gut, which is retained twice as much compared to young limiting the amount of leucine that makes it into the blood stream. Resistance to leucine-stimulated protein synthesis also occurs at the cellular level in aging cells. Results in both younger and older adults have shown that supplementation with leucine enhances the MPS response, namely when a suboptimal dose of protein is consumed. Research suggests that supplemental leucine can augment muscle protein synthesis when a suboptimal dose of protein is consumed, but supplemental leucine will not confer additional benefit if a protein bolus sufficient to maximally stimulate muscle protein synthesis is consumed.

Benefits

Leucine activates protein synthesis by signaling through the mTOR pathway. When leucine levels are sufficient, it stimulates mTOR, which in turn promotes the synthesis of proteins necessary for muscle growth and repair. This mechanism is particularly important during periods of muscle recovery after exercise, as well as in older adults who may experience anabolic resistance.

How it works

Leucine supplementation has several benefits, particularly for muscle gain and exercise performance. It enhances muscle protein synthesis, which is crucial for muscle recovery and growth. Additionally, leucine can help improve body composition by promoting fat loss while preserving lean muscle mass. It may also play a role in regulating blood sugar levels and improving metabolic health.

Side effects

Leucine tends to be supplemented in the 2,000-5,000mg range for acute usage. It tends to be taken either in a fasted state or alongside meals with an inherently low protein content (or protein sources that are low in leucine).

Dosage

Leucine is generally considered safe when taken in appropriate doses. However, excessive intake may lead to potential side effects such as gastrointestinal discomfort, nausea, and diarrhea. Individuals with certain medical conditions, such as maple syrup urine disease, should avoid leucine supplementation. It is advisable to consult a healthcare provider before starting any new supplement.