Liver Blood Tests: AST, ALT, GGT, Alkaline Phosphatase, and Bilirubin — What They Mean

The liver is one of the largest organs in the body and directly determines how well your body can lose fat, build muscle, and maintain immune function. If it's impaired, none of the rest of the system works properly.

Why the Liver Matters for Body Composition

Fat metabolism: Carbohydrate and fat metabolism both occur primarily in the liver. A compromised liver directly impairs fat oxidation.

Protein synthesis: Transport proteins (albumins) are produced in the liver. Without adequate albumin, testosterone cannot be transported through the bloodstream to muscle tissue.

Hormone elimination: Fat-soluble hormones like estradiol and cortisol are broken down in the liver. When liver function is impaired, estradiol accumulates, suppressing gonadotropic hormones and consequently reducing testosterone. Elevated cortisol drives insulin resistance and fat accumulation.

Immune function: Immune globulins are produced in the liver. Poor liver function → compromised immunity.

Blood sugar regulation: The liver stores glycogen and releases glucose to maintain blood sugar. This is a critical buffer against hypoglycemia during intense training.

The Five Tests to Monitor

AST (Aspartate Aminotransferase)

Found primarily in the heart muscle, then liver. Elevated AST with normal ALT can indicate myocardial damage — not liver disease. The classic mistake is assuming high AST alone means liver problems. Significantly elevated AST = see a cardiologist first.

ALT (Alanine Aminotransferase)

Found primarily in the liver, then kidneys and pancreas. Elevated ALT with normal AST is more specifically a liver indicator. Elevated ALT can indicate hepatitis or other liver pathology.

The De Ritis Ratio (AST:ALT): Only meaningful for identifying the source of enzyme elevation. A doctor uses this ratio to distinguish cardiac from hepatic damage. Don't interpret it alone.

If both AST and ALT are significantly elevated: tissue necrosis is possible — see a doctor immediately.

GGT (Gamma-Glutamyl Transferase)

Another liver enzyme. Concentrated in liver tissue; elevated GGT indicates liver stress or damage. Pattern of elevation in relation to AST/ALT helps differential diagnosis.

ALP (Alkaline Phosphatase)

Active in alkaline environments; found in liver and bone. An elevation could indicate liver damage OR bone healing from a fracture. Context matters.

Bilirubin (Total, Direct, Indirect)

Red blood cells die after ~4 months. The liver breaks them down, converting insoluble indirect bilirubin to soluble direct bilirubin for excretion.

• Elevated indirect (unconjugated): may indicate excessive erythrocyte destruction or impaired liver conversion
• Elevated direct (conjugated): may indicate blocked bile ducts (gallstones, tumor)
• Always test both fractions — "total bilirubin" alone doesn't localize the problem

When to Test and How

Before testing: no heavy training for 3-4 days (intense exercise causes muscle fiber breakdown, elevating enzyme levels temporarily), no alcohol for 3 days, test fasted in the morning.

Target: all values should be in the middle of the normal range, not merely below the upper limit. Upper-limit "normal" means you'll be outside normal as soon as any stress is added.

If anything is significantly elevated: see a doctor. Do not self-medicate. The ratios between these five markers require medical interpretation — a single abnormal value cannot identify the problem without understanding the pattern.

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