Causes of Non-Alcoholic Fatty Liver Disease (NAFLD)
NAFLD is fundamentally caused by metabolic dysfunction and insulin resistance, manifesting when hepatic fat accumulation exceeds 5% of liver weight in the absence of significant alcohol consumption (>21 standard drinks/week in men, >14 drinks/week in women) or other secondary causes of steatosis. 1, 2, 3
Primary Metabolic Causes
The core pathophysiology centers on cardiometabolic risk factors that drive hepatic steatosis:
- Obesity - Present in 70% of NAFLD cases 4
- Type 2 diabetes - NAFLD prevalence exceeds 70% in diabetic patients, with diabetes being a major risk factor for disease progression 1
- Insulin resistance - The fundamental metabolic dysfunction driving fat accumulation 3, 5
- Dyslipidemia - Particularly atherogenic dyslipidemia 3
- Hypertension - Part of the metabolic syndrome cluster 3
These conditions create a state of lipotoxicity through increased hepatic de novo lipogenesis, impaired fatty acid oxidation, and defective apolipoprotein secretion 6.
Secondary Causes to Exclude
Before diagnosing NAFLD, you must systematically exclude competing etiologies 7, 8, 9:
Macrovesicular Steatosis Causes:
- Excessive alcohol consumption (defined above)
- Hepatitis C (particularly genotype 3) 10
- Medications: amiodarone, methotrexate, tamoxifen, corticosteroids, valproate, antiretrovirals 7, 10
- Wilson's disease
- Parenteral nutrition
- Severe malnutrition/starvation
- Lipodystrophy
- Abetalipoproteinemia 7
Other Liver Diseases to Rule Out:
- Hemochromatosis (check ferritin, transferrin saturation, HFE gene if elevated) 8, 9
- Autoimmune hepatitis (low-titer autoantibodies common in NAFLD but usually clinically insignificant) 9
- Chronic viral hepatitis B
- Alpha-1 antitrypsin deficiency 9
Pathophysiological Mechanisms
The disease progression involves multiple interconnected pathways 5, 11:
- Adipose tissue dysfunction - Releases excess free fatty acids into circulation
- Hepatic lipid accumulation - Overwhelms hepatocyte capacity
- Mitochondrial dysfunction - Impaired beta-oxidation and increased oxidative stress
- Inflammation - Macrophage activation and cytokine release
- Hepatic stellate cell activation - Drives fibrosis progression
- Intestinal dysbiosis - Altered gut microbiota contributes to disease 11
Dietary and Environmental Factors
Western dietary patterns directly contribute to NAFLD development 12, 13:
- Harmful components: Saturated fats, trans-fats, simple sugars (especially fructose), processed meats, sugar-sweetened beverages
- Protective components: Monounsaturated fats (MUFA), omega-3 polyunsaturated fats (PUFA), plant-based proteins, dietary fiber, Mediterranean diet adherence 12
Genetic Predisposition
NAFLD demonstrates significant heritability (estimated 0.386-0.521 for liver fat fraction) 9. Familial clustering occurs, with 18% of NASH patients having similarly affected first-degree relatives 7, 8. Specific gene variants (including HFE mutations, PNPLA3, TM6SF2) increase susceptibility and progression risk 11.
Clinical Pitfalls
- Normal liver enzymes do not exclude NAFLD - ALT/AST can be normal in significant disease 8
- Mildly elevated ferritin is common in NAFLD and doesn't necessarily indicate iron overload 8, 9
- Low-titer autoantibodies (ANA >1:160 or ASMA >1:40) occur in 21% of NAFLD patients and are typically clinically insignificant 9
- AST:ALT ratio <1** suggests metabolic NAFLD, while **ratio >2 suggests alcohol-related disease 4
The emerging term Metabolic dysfunction-Associated Steatotic Liver Disease (MASLD) replaces NAFLD to emphasize the positive diagnosis based on cardiometabolic risk factors rather than alcohol exclusion alone 1.