What are the causes, pathogenesis, and treatment options for non‑alcoholic fatty liver disease (NAFLD)?

Causes and Pathogenesis of NAFLD

NAFLD is fundamentally caused by excessive caloric intake (particularly from saturated fats, trans-fats, simple sugars, and animal proteins) combined with sedentary behavior, leading to hepatic lipid accumulation in the setting of insulin resistance and metabolic dysfunction. 1, 2

Primary Causes

NAFLD develops through a "multiple-hit" pathogenesis involving:

• Metabolic dysfunction: Obesity, insulin resistance, type 2 diabetes, hypertension, and dyslipidemia are the core drivers 2
• Dietary factors: Western dietary patterns rich in processed foods, sugar-sweetened beverages, red meat, and saturated fats directly promote hepatic steatosis 1
• Genetic susceptibility: Predisposing genetic variants interact with environmental factors to disturb lipid homeostasis 3

Pathophysiological Mechanisms

The disease progresses through interconnected pathways:

Lipotoxicity is the central mechanism—excessive triglyceride and toxic lipid species accumulation in hepatocytes triggers endoplasmic reticulum stress, mitochondrial dysfunction, and disturbed autophagy 3, 4. This leads to hepatocyte injury and death, which activates inflammatory cascades and hepatic stellate cells, driving progression from simple steatosis to steatohepatitis (NASH) and fibrosis 5, 3.

Insulin resistance amplifies lipid accumulation by increasing hepatic de novo lipogenesis and impairing fatty acid oxidation 2, 3. Gut dysbiosis further contributes through altered metabolite production and increased intestinal permeability 6, 3.

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Treatment of NAFLD

Weight loss through caloric restriction and increased physical activity is the only proven treatment for NAFLD, with 5-7% weight loss improving steatosis and inflammation, and ≥10% weight loss potentially reversing fibrosis. 2, 7

Treatment Algorithm by Disease Severity

All NAFLD Patients (Regardless of Severity)

Lifestyle modifications are mandatory for everyone 8:

1. Weight loss targets:

   • Achieve 5-7% body weight reduction to improve steatosis and inflammation 2, 7
   • Target ≥10% weight loss to improve fibrosis 2, 7
   • Gradual weight loss (<1 kg/week) is safer than rapid reduction 8

2. Dietary modifications 2:

   • Reduce total caloric intake by 500-1000 kcal/day (target 1200-1500 kcal/day for women, 1500-1800 kcal/day for men) 8
   • Adopt Mediterranean diet pattern—this improves NAFLD even without weight loss 1, 9, 2
   • Eliminate: sugar-sweetened beverages, processed foods, saturated fats, trans-fats, simple sugars 1, 9
   • Increase: monounsaturated fats (extra virgin olive oil), omega-3 fatty acids, plant-based proteins, dietary fiber, whole grains, vegetables, fruits 1, 9

3. Physical activity 10, 7:

   • Minimum 150 minutes/week of moderate-intensity aerobic exercise 11
   • Vigorous-intensity exercise (≥6 METs) is required to improve fibrosis 7
   • Add resistance training twice weekly 11

4. Manage metabolic comorbidities 8:

   • Treat diabetes, hypertension, and dyslipidemia per standard guidelines
   • Statins are safe and should be used for cardiovascular risk reduction 5, 11

Biopsy-Proven NASH with Fibrosis

Pharmacological treatment should be reserved for patients with biopsy-proven NASH and fibrosis 5, 11, 7:

For patients with type 2 diabetes and NASH:

• Pioglitazone improves histological features of NASH 5, 2
• GLP-1 receptor agonists (e.g., dulaglutide) reduce liver fat and improve metabolic parameters 2, 12

For non-diabetic patients with biopsy-proven NASH:

• Vitamin E (800 IU/day) improves steatohepatitis 5, 11
• Consider combination with high-dose ursodeoxycholic acid 11

Important caveats: Metformin is NOT indicated for NAFLD treatment (though safe if needed for diabetes) 5, 11. No FDA-approved medications specifically for NAFLD exist 2.

Severe Obesity (BMI ≥35-40 kg/m²)

Bariatric surgery should be considered when meeting national eligibility criteria 2, 13:

• Resolves NASH in 85% of patients at 1 year 13
• Improves fibrosis in 30% of patients 13
• Safe even in compensated cirrhosis 13
• Provides cardiovascular and mortality benefits beyond liver improvement 13

Advanced Fibrosis and Cirrhosis

These patients require secondary care management 13:

• 6-monthly ultrasound surveillance for hepatocellular carcinoma 13
• Endoscopic screening for varices 5
• Monitor for decompensation (ascites, encephalopathy, variceal bleeding) 5
• Refer for transplant evaluation if MELD score ≥10 or decompensation occurs 5, 13

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Common Pitfalls to Avoid

• Do not wait for elevated liver enzymes—ALT/AST may be normal in NAFLD 2
• Do not prescribe pharmacotherapy for simple steatosis without NASH/fibrosis—the risk-benefit ratio is unfavorable 11, 7
• Do not recommend rapid weight loss—this can worsen portal inflammation and fibrosis 8
• Do not advise alcohol abstinence universally—while heavy drinking is harmful, guidelines do not support prescribing light-moderate alcohol as therapy, but also don't mandate complete abstinence 11
• Do not avoid statins in NAFLD—they reduce cardiovascular risk and may decrease HCC incidence 5, 11, 8

The evidence strongly supports that lifestyle modification is both necessary and sufficient for most NAFLD patients, with pharmacotherapy reserved only for those with histologically confirmed NASH and significant fibrosis where the risk of progression justifies medication risks 5, 11, 7.