leuciin

Leuciin, known in many languages as leucine, is an essential amino acid and one of the branched-chain amino acids (BCAAs) required in the human diet. It occurs in many dietary proteins and is typically present in relatively high amounts in animal products such as dairy, eggs, meat, and fish, as well as in some plant proteins.

Biological role and metabolism

Leuciin plays a key role in protein synthesis, influencing muscle maintenance and growth. It strongly activates the mTOR signaling pathway, which promotes translation and muscle protein production. In addition to its role in synthesis, leuciin can serve as an energy source during prolonged exercise or fasting through its ketogenic metabolism, yielding acetyl-CoA and acetoacetate. After uptake by tissues, leuciin undergoes transamination to α-ketoisocaproate (KIC) and is subsequently degraded by the branched-chain α-ketoacid dehydrogenase complex.

Dietary sources and supplementation

Leuciin is abundant in high-quality protein sources, particularly dairy products, meat, poultry, eggs, and soy. It is also available as a dietary supplement, frequently used by athletes to support muscle recovery and by older adults to counteract sarcopenia. Typical dietary intakes vary with protein consumption and dietary patterns.

Health, safety, and interactions

Leuciin is an essential nutrient, and deficiency is rare in balanced diets. Individuals with metabolic disorders such as maple syrup urine disease or certain liver or kidney conditions should manage BCAA intake under medical supervision. Excessive supplementation can disrupt amino acid balance and has potential adverse effects in susceptible individuals; always consider medical advice for specific health conditions or treatment plans.