Non-alcoholic fatty liver disease (NAFLD) is the most prevalent chronic liver condition worldwide, affecting an estimated 25–30% of the general adult population and up to 75–90% of individuals with obesity or type 2 diabetes. It is defined by fat accumulation in more than 5% of liver cells, in the absence of significant alcohol consumption or other secondary causes.

NAFLD ranges from simple fat accumulation to non-alcoholic steatohepatitis (NASH), fibrosis, cirrhosis, and liver cancer. It is widely recognised as the hepatic expression of metabolic syndrome, closely linked to insulin resistance, visceral obesity, elevated triglycerides, hypertension, and impaired blood sugar regulation.

Critically, early-stage NAFLD is reversible with targeted lifestyle and nutritional interventions.

Disease Spectrum and Staging

NAFLD progresses along a histological spectrum:

Simple steatosis: Fat accumulation without significant inflammation or scarring. Largely reversible with low risk of progression in isolation.

NASH: Steatosis with lobular inflammation, hepatocyte injury, and early fibrosis. Affects 10–25% of NAFLD patients.

Fibrosis: Progressive scarring from chronic inflammation. Fibrosis stage is the strongest predictor of liver-related and all-cause mortality.

Cirrhosis: Extensive scarring with loss of normal liver architecture.

Early Symptoms and Diagnostic Indicators

NAFLD is largely silent in early stages and is most often discovered incidentally through abnormal liver enzymes or imaging performed for unrelated reasons.

When symptoms are present, they are non-specific:

Hepatic symptoms:

• Right upper quadrant discomfort or heaviness
• Fatigue — among the most commonly reported symptoms
• Nausea, particularly after fatty meals

Metabolic signs:

• Acanthosis nigricans — dark, velvety skin in skin folds; a marker of insulin resistance
• Multiple skin tags — independently associated with insulin resistance and metabolic syndrome
• Abdominal obesity — waist circumference is a stronger predictor of NAFLD than BMI

Laboratory markers:

• ALT: Elevated in 50–70% of NAFLD patients.
• GGT: An early, sensitive marker of hepatic oxidative stress.
• Fasting triglycerides: Reflect impaired hepatic fat export; both a cause and consequence of NAFLD.
• Fasting insulin / HOMA-IR: HOMA-IR above 2.5 is associated with significantly elevated NAFLD risk.
• Uric acid: An independent risk factor for NAFLD, likely via fructose-driven mechanisms and mitochondrial oxidative stress.

Imaging: Hepatic ultrasound is the standard first-line investigation. FibroScan offers superior sensitivity for mild steatosis and non-invasive fibrosis staging.

Pathophysiology: The Multiple Parallel-Hit Model

1. Insulin resistance and de novo lipogenesis

Insulin resistance drives excess fat production in the liver (de novo lipogenesis), while reducing fatty acid oxidation. Fructose is a particularly potent driver — unlike glucose, it bypasses normal glycolytic regulation and is metabolised almost exclusively in the liver, directly activating fat synthesis pathways.

2. Gut-liver axis dysfunction

Approximately 70% of hepatic blood supply comes from the portal vein draining the intestine. In gut barrier dysfunction ("leaky gut"), bacterial lipopolysaccharides (LPS) enter portal circulation and activate hepatic immune cells, triggering the inflammatory cascade central to NASH progression. Gut microbiome composition is significantly altered in NAFLD, with reduced barrier-protective species and increased LPS-producing bacteria.

3. Mitochondrial dysfunction and oxidative stress

Impaired mitochondrial fat burning and increased reactive oxygen species (ROS) production drive the transition from simple steatosis to NASH, triggering hepatocyte injury and activation of fibrosis-generating stellate cells.

4. Visceral fat inflammation and lipotoxicity

Visceral adipose tissue releases excess free fatty acids and inflammatory cytokines (TNF-α, IL-6) into portal circulation, directly damaging hepatocytes. Anti-inflammatory adiponectin — markedly reduced in visceral obesity — is independently associated with NASH severity.

5. Endocrine disruption

Hypothyroidism reduces hepatic fatty acid oxidation and fat export, promoting steatosis. A meta-analysis confirmed a significantly elevated NAFLD risk in hypothyroid patients.

Evidence-Based Interventions

Dietary Modification

Mediterranean diet. The Mediterranean dietary pattern has the strongest evidence base among dietary interventions for NAFLD.

Physical Activity

Exercise reduces hepatic fat both through reduction of visceral adiposity and direct metabolic effects on the liver, independent of weight loss. Resistance training is particularly effective for improving insulin sensitivity via GLUT4 upregulation in skeletal muscle.

Targeted Nutritional Support

Omega-3 fatty acids — Marine omega-3s suppress hepatic fat synthesis (via SREBP-1c inhibition) and promote fat oxidation (via PPARα activation).

Silymarin — Silymarin supports hepatocyte protection, glutathione synthesis, and bile flow.

Choline. Essential for VLDL assembly and hepatic fat export. Choline deficiency directly causes steatosis by impairing triglyceride clearance from the liver.

Probiotics. Probiotic supplementation can significantly reduce liver enzymes, liver fat, and inflammatory markers in NAFLD, acting via improved gut barrier integrity and reduced LPS translocation.

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