1.     When “Healthy Habits” Backfire: Why Well-Intentioned Practices Can Damage the Liver

The recommended daily protein intake is approximately 0.8–1 g per kilogram of body weight. Significantly exceeding this places excessive strain on the liver and kidneys.

Excess protein generates ammonia during breakdown. The liver detoxifies this through the “urea cycle,” so high protein consumption increases this detoxification workload.

A Hepatologist’s Perspective: The Relationship Between Excess Protein and Liver Function

For those who already have impaired liver function or fatty liver, the metabolic burden of protein is greater than for healthy individuals, making elevation of ALT and AST more likely. Intake tailored to one’s own physical condition is essential.

Expert Insight: Ammonia Detoxification and L-Carnitine Supplementation

Clinical research has reported the effectiveness of L-carnitine supplementation therapy in advanced liver disease. Inability to process ammonia from excess protein consumption poses risks to the brain and entire body. Professional assessment of the liver’s processing capacity is important.

2.     The Real Causes of ALT (GPT) Elevation

ALT (alanine aminotransferase) is an enzyme released into the bloodstream when liver cells are damaged. The reference range is 30 U/L or below.

Mechanisms of ALT elevation from supplements and protein:

• Direct damage to liver cells by components

• Increased liver burden from excess protein metabolism

• Unexpected hepatotoxicity from interactions between multiple components

Clinical Knowledge: Hidden Fatty Liver Risk at ALT ≥ 16

When ultrasound examination is performed on outpatients whose ALT is within the reference range but at 16 U/L or above, fatty liver is frequently found. Clinical research has shown that “hidden obesity”—thin appearance with visceral fat accumulation—adversely affects long-term prognosis. Even within reference ranges, “multifaceted diagnosis that captures subtle changes in values is the key to early detection.”

3. Damage to the Liver from Excessive Protein Intake

Whether plant-based or animal-based, the issue with protein and liver impact is quantity rather than type. Regular intake of 2–3 or more servings daily (25–30 g each) warrants periodic liver function checks.

Those who should be particularly cautious:

• Those with liver disease

• Those with reduced kidney function

• Users of steroid-type supplements or high-dose BCAA

Expert Insight: Proper Use of BCAA and Energy Metabolism

In clinical settings, BCAA (branched-chain amino acids) are used to support muscle metabolism and reduce liver burden. Clinical research has demonstrated that appropriate BCAA supplementation under proper medical management maintains and improves whole-body energy metabolism. Self-directed overuse can exhaust the liver.

4.     How to Correctly Interpret Liver Function Test Values (AST, ALT, γ-GTP)

Interpreting these three values in combination is important:

• AST: Present in the liver, heart, and skeletal muscle. Elevation together with ALT indicates hepatocyte damage.

• ALT: Specific to liver cells. Particularly likely to rise with supplement and protein-related damage.

• γ-GTP: Responds sensitively to alcohol and drug-induced liver damage. Can also rise with supplement-related damage.

Hepatology specialists make comprehensive judgments from the patterns of these three values to estimate causes and determine appropriate responses. Self-diagnosis is dangerous; abnormal values should always be consulted with a specialist.

5. Guidelines for Safe Supplement and Protein Use

Four key points for safe use:

• Check for quality certification marks: GMP- and NSF-certified products have robust quality management

• Select products with clearly stated single ingredients: products with clear ingredient quantities rather than complex formulations

• Consult a physician if you have liver disease: an essential step

• Prioritize food sources as the basis: obtaining nutrients from a balanced diet is the safest and most effective approach

6. A Message from Your Hepatologist

At our clinic, we have seen cases where liver function deteriorated due to protein and supplements that patients thought were beneficial. The liver is the “silent organ,” making symptoms difficult to notice; regular blood tests are therefore important.

If elevation of AST, ALT, or γ-GTP is observed, immediately discontinue all supplements and protein. If AST > ALT, the liver is in the process of worsening with liver failure risk. If values do not improve after discontinuation, hospitalization treatment may need to be considered.