The oxidation energy supply characteristics of L-leucine

As the branched-chain amino acid (BCAA) with the highest oxidative energy supply efficiency, L-leucine can provide energy through three pathways: "direct oxidation in skeletal muscle, ketone body formation, and gluconeogenesis." In scenarios with surging energy demands such as high-intensity exercise or starvation, it accounts for 10%–15% of total energy supply. Notably, its oxidation does not rely on liver metabolism, enabling rapid ATP provision to tissues.

I. Core Metabolic Pathways of Oxidative Energy Supply

Direct Oxidation in Skeletal Muscle (Main Pathway)

L-leucine is first catalyzed by branched-chain amino acid transaminase (BCAT) in skeletal muscle cells to form α-ketoisocaproate (KIC). It then undergoes oxidative decarboxylation via the branched-chain α-ketoacid dehydrogenase (BCKDH) complex, enters the tricarboxylic acid (TCA) cycle for complete decomposition, and ultimately generates CO₂, H₂O, and ATP. This pathway operates independently of the liver with high reaction rates, serving as a crucial energy source for skeletal muscle during exercise.

Ketone Body Formation for Energy (Secondary Pathway)

A portion of α-ketoisocaproate is further metabolized in the liver or kidneys to produce ketone bodies such as acetoacetate and β-hydroxybutyrate. These ketone bodies can be taken up by tissues like the brain and myocardium, converted to acetyl-CoA, and then enter the TCA cycle for energy supply. Particularly during starvation or prolonged exercise, the proportion of energy derived from ketone bodies increases significantly.

Gluconeogenesis-Assisted Energy Supply

Acetyl-CoA produced by L-leucine oxidation can be converted to glucose precursors via the glyoxylate cycle, participating in gluconeogenesis to generate glucose. This provides energy for glucose-dependent tissues (e.g., brain tissue), achieving complementary energy metabolism.

II. Key Characteristics of Oxidative Energy Supply

High Energy Efficiency with Dynamic Priority Adjustment

Complete oxidation of 1 mol of L-leucine yields approximately 32 mol of ATP, with energy efficiency close to that of glucose (36–38 mol ATP/mol). At rest, L-leucine contributes only 2%–5% of total energy; however, during high-intensity exercise (e.g., sprinting, strength training) or starvation, the uptake and oxidation rate in skeletal muscle increase 3–5 times, with energy contribution reaching 10%–15%, making it one of the main energy sources.

Liver-Independent Metabolism to Avoid Metabolic Burden

Unlike other amino acids, L-leucine oxidation primarily occurs in peripheral tissues such as skeletal muscle and myocardium, with the liver only involved in minor ketone body formation. Even under high liver functional load, it can still supply energy normally, making it suitable as an energy supplement under special physiological conditions.

Synergistic Regulation with Carbohydrate and Lipid Metabolism

L-leucine oxidation inhibits the activity of fat synthase and promotes fat breakdown for energy. Meanwhile, it activates the AMPK signaling pathway to enhance cellular glucose uptake and utilization, achieving synergistic balance among carbohydrate, lipid, and amino acid metabolism and avoiding excessive consumption of a single energy substrate.

III. Key Factors Influencing Oxidative Energy Supply

Body Energy Status

When energy intake is insufficient (starvation, dieting) or demand increases (exercise, stress), the activity of L-leucine oxidases (e.g., BCKDH) rises significantly, enhancing oxidative energy supply. During energy surplus, the oxidation rate decreases, and excess L-leucine is more likely to participate in protein synthesis or be converted to fat for storage.

Exercise Intensity and Duration

During low-intensity exercise, L-leucine contributes little to energy supply. For high-intensity, prolonged exercise (exceeding 60 minutes), muscle glycogen reserves decline, and the proportion of energy from L-leucine oxidation gradually increases, becoming an important supplement to maintain exercise capacity.

Levels of Other Nutrients

Sufficient carbohydrate intake inhibits L-leucine oxidation, prioritizing glucose for energy. Insufficient fat intake leads to a compensatory increase in L-leucine oxidation rate. B vitamins (e.g., vitamin B1, B2) act as coenzymes for oxidases; their deficiency reduces L-leucine’s oxidative energy supply efficiency.

IV. Practical Application Significance

Sports Nutrition Supplementation

Supplementation of L-leucine for high-intensity athletes can rapidly supply energy to skeletal muscle, delay fatigue, reduce muscle protein breakdown, and promote post-exercise recovery. It is recommended to supplement 2–5g per serving 30 minutes before exercise or during exercise.

Energy Support for Special Populations

For individuals in starvation, post-surgical recovery, or with chronic consumptive diseases, L-leucine supplementation provides efficient energy, reduces liver metabolic burden, maintains muscle mass, and prevents malnutrition.

Weight Management Assistance

L-leucine oxidation promotes fat breakdown and induces strong satiety. Appropriate supplementation helps control total caloric intake while avoiding muscle loss, making it suitable for individuals aiming for fat loss.