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Understanding Fatty Liver Disease
A detailed educational guide to non-alcoholic fatty liver disease (NAFLD/MASLD), its stages, lab values, and what the science tells us.
The 5 Stages of Liver Disease
Healthy Liver
Normal liver with less than 5% fat content. Performs all 500+ functions optimally. All lab values within normal ranges. Ultrasound shows normal echogenicity (brightness pattern).
Steatosis (Fatty Liver)
Fat accumulates in more than 5% of liver cells. Usually asymptomatic (no symptoms). ALT may be mildly elevated. Ultrasound shows increased echogenicity (brighter than kidneys). REVERSIBLE with dietary changes.
NASH (Steatohepatitis)
Non-Alcoholic Steatohepatitis — fat PLUS inflammation and liver cell damage (hepatocyte ballooning). ALT and AST elevated. GGT often elevated. Fatigue and right upper quadrant discomfort may appear. Still potentially REVERSIBLE but requires significant lifestyle changes.
Fibrosis
Scar tissue begins to replace healthy liver tissue. Graded F1-F4 on the METAVIR scale. Liver function begins to decline. FibroScan (transient elastography) measures liver stiffness in kPa (kilopascals). Early fibrosis (F1-F2) may still be partially reversible. Advanced fibrosis (F3-F4) is harder to reverse.
Cirrhosis
Extensive scarring with loss of normal liver architecture. Liver function severely compromised. Risk of portal hypertension (high blood pressure in the portal vein system), ascites (fluid in abdomen), variceal bleeding, and hepatocellular carcinoma (liver cancer). May require liver transplantation. NOT reversible.
Key Lab Values Explained
| Test | Normal Range | What It Tells You |
|---|---|---|
| ALT | 7-56 U/L | Liver cell damage marker. Elevated in fatty liver. |
| AST | 10-40 U/L | Liver and muscle damage. AST/ALT ratio helps differentiate causes. |
| GGT | 9-48 U/L | Bile duct obstruction, alcohol use, fatty liver indicator. |
| Triglycerides | <150 mg/dL | Blood fat levels. Elevated = liver producing excess fat. |
| Fasting Glucose | 70-100 mg/dL | Blood sugar levels. 100-125 = pre-diabetes. >126 = diabetes. |
| HbA1c | <5.7% | 3-month blood sugar average. 5.7-6.4% = pre-diabetes. >6.5% = diabetes. |
Imaging: What Ultrasound Shows
Ultrasound (ecografia) is the first-line imaging study for fatty liver. The radiologist compares the echogenicity (brightness) of the liver to the right kidney:
- ● Normal: liver and kidney have similar brightness
- ● Grade 1: liver slightly brighter than kidney
- ● Grade 2: liver much brighter, blood vessels becoming harder to see
- ● Grade 3: liver very bright, blood vessels and diaphragm obscured
Selected References
Younossi ZM, et al. "Global epidemiology of nonalcoholic fatty liver disease." Hepatology, 2023. DOI: 10.1002/hep.32660
Rinella ME, et al. "A multisociety Delphi consensus statement on new fatty liver disease nomenclature." Hepatology, 2023. DOI: 10.1097/HEP.0000000000000520
Lustig RH. "Fructose: It's alcohol without the buzz." Advances in Nutrition, 2013. DOI: 10.3945/an.112.002998
Stefan N, et al. "A global view of the interplay between non-alcoholic fatty liver disease and diabetes." Lancet Diabetes Endocrinol, 2022. DOI: 10.1016/S2213-8587(22)00003-1
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