ALT

Why It Matters

Alanine aminotransferase, or ALT, is a liver enzyme made in the cytosol of liver cells. This enzyme plays an important role in amino acid metabolism and gluconeogenesis. While this enzyme is primarily found in the liver, it is also found in skeletal muscle. While these enzymes are typically found in the blood at low levels, any compromise of liver or muscle cell integrity can cause an increase in ALT concentrations (source, source, source). ALT levels have been shown to correlate with components of health-related physical fitness, suggesting that liver function and physical performance are closely linked (source).

Low ALT: Reduced Liver Enzyme Activity and Metabolic Limitation

Low blood ALT levels can be influenced by physiological factors related to liver and muscle health and function. From a nutritional perspective, deficiencies in certain vitamins and minerals that are essential for liver function can also negatively affect levels (source).

Potential Performance Impact

• Impaired amino acid metabolism limiting energy production and recovery
• Reduced gluconeogenesis affecting endurance performance
• Compromised nitrogen balance potentially impacting muscle maintenance

Lifestyle and Physiological Contributors

• Vitamin B6 deficiency (ALT requires pyridoxal phosphate as a cofactor)
• Poor protein intake or malnutrition
• Chronic kidney disease or uremia
• Hypothyroidism
• Regular cardiovascular exercise (lower baseline liver enzyme activity)

Optimal ALT: Liver Efficiency and Metabolic Health

ALT levels within the optimal range suggest that liver cells are functioning properly with minimal damage or stress. This reflects good liver health, supporting efficient amino acid metabolism, gluconeogenesis, and energy production — all critical processes for athletic performance.

Potential Performance Benefits

• Efficient amino acid metabolism supporting energy production and recovery
• Optimal gluconeogenesis for sustained endurance
• Good liver function supporting overall metabolic health

High ALT: Liver Stress, Inflammation, and Recovery Compromise

Elevated ALT levels indicate liver cell damage or stress, which can have significant implications for athletic performance and recovery. It can also be caused by muscle damage due to intense exercise (source).

Potential Performance Impact

• Impaired liver function affecting energy metabolism and recovery
• Increased inflammation potentially impacting performance
• Reduced protein synthesis and muscle repair
• Compromised detoxification potentially affecting overall health

Lifestyle and Physiological Contributors

• Intense or excessive exercise causing muscle damage
• High alcohol consumption
• Non-alcoholic fatty liver disease (NAFLD)
• Certain medications (statins, NSAIDs, antibiotics)
• Viral hepatitis or other liver conditions
• Obesity and metabolic syndrome

Notes

While ALT is primarily a marker of liver health, it can be slightly elevated after intense exercise due to muscle cell breakdown. Athletes should consider this when interpreting their results, especially after particularly strenuous training or competition.