Fatty Liver Disease (NAFLD/MASLD) — Causes, Symptoms & Treatment Guide — Symptoms, Causes & Treatment | MyMedicPlus

Fatty liver disease refers to a spectrum of liver conditions characterised by excessive fat accumulation (hepatic steatosis — above 5% of hepatocytes containing triglyceride droplets) in the liver. The two main types are: non-alcoholic fatty liver disease (NAFLD) — now renamed MASLD (metabolic dysfunction-associated steatotic liver disease) in 2023 to better reflect its metabolic aetiology — occurring in the absence of significant alcohol consumption; and alcoholic liver disease (ALD/MetALD) — caused by heavy alcohol use. NAFLD/MASLD is the most common liver disorder globally, affecting approximately 25-32% of the global adult population (approximately 2 billion people). The spectrum of NAFLD progresses from simple steatosis (isolated fat accumulation — generally benign) to NASH (non-alcoholic steatohepatitis — now MASH: metabolic dysfunction-associated steatohepatitis — steatosis with liver inflammation and hepatocyte injury) to advanced fibrosis and cirrhosis. Approximately 3-5% of adults have NASH, of whom 10-30% will develop advanced fibrosis over 10 years, and 5-10% will develop cirrhosis. NAFLD is now the leading cause of liver transplantation in women in the United States and is projected to become the leading cause overall. Cirrhosis from NASH confers a 2-3% annual risk of hepatocellular carcinoma (HCC). The 2023 Delphi consensus renamed NAFLD to MASLD (metabolic-associated steatotic liver disease) to reduce stigma and improve diagnostic precision.

MASLD/NAFLD is driven by metabolic dysregulation — insulin resistance is the central pathophysiological mechanism. Insulin resistance causes increased lipolysis from adipose tissue, delivering excess free fatty acids (FFA) to the liver; combined with increased hepatic de novo lipogenesis from dietary carbohydrates, this overwhelms the liver's capacity to oxidise or export fat, causing triglyceride accumulation. The 'two-hit' or 'multiple-hit' hypothesis: simple steatosis is the first hit; a second hit (oxidative stress, mitochondrial dysfunction, gut dysbiosis — altered gut microbiome with increased intestinal permeability — lipid peroxidation, cytokine activation from adipose tissue) causes progression from steatosis to NASH and fibrosis. Risk factors: obesity (the strongest risk factor — NAFLD prevalence above 80% in class III obesity; visceral adiposity, not total body fat, is the most important correlate); type 2 diabetes (70-75% of T2DM patients have NAFLD; 30-40% have NASH); metabolic syndrome (abdominal obesity + insulin resistance + hypertriglyceridaemia + low HDL + hypertension — all components); hyperlipidaemia; polycystic ovary syndrome (PCOS); hypothyroidism; sleep apnea (hypoxia drives de novo lipogenesis); genetic factors (PNPLA3 I148M variant — tripled NAFLD risk and doubles risk of cirrhosis; TM6SF2 E167K; MBOAT7 — identified in genome-wide association studies); and gut microbiome (dysbiosis increases hepatic delivery of endotoxin and short-chain fatty acids from microbial fermentation). Fructose overconsumption (sugar-sweetened beverages — fructose is preferentially converted to liver fat); ultra-processed foods. Non-metabolic causes of fatty liver: alcoholic liver disease (more than 21 units/week for men, 14 for women); medications (amiodarone, methotrexate, tamoxifen, corticosteroids, valproate, antiretrovirals); rare genetic metabolic diseases (Wilson's disease, lipodystrophy).

Simple steatosis and early NASH are almost always asymptomatic — detected incidentally on ultrasound or through elevated liver enzymes on routine blood testing. When symptoms occur, they are non-specific: fatigue and malaise (the most common complaint); right upper quadrant discomfort or a dull ache (from hepatomegaly — enlarged liver); and general malaise. Clinical examination may reveal hepatomegaly. Liver function tests: ALT and AST are elevated in NASH (typically 1-4x upper limit of normal); isolated steatosis may have normal LFTs (LFTs do not reliably distinguish simple steatosis from NASH — liver biopsy remains the gold standard). Advanced disease features — develop as NASH progresses to cirrhosis: jaundice; ascites (abdominal fluid accumulation from portal hypertension — abdominal distension, shifting dullness); variceal bleeding (oesophageal varices — haematemesis or melaena — often the first dramatic presentation of cirrhosis); encephalopathy (confusion, asterixis, altered consciousness from hepatic failure); splenomegaly (portal hypertension); peripheral oedema; spider naevi and palmar erythema (signs of chronic liver disease); and hepatocellular carcinoma (HCC — NASH cirrhosis confers 2-3% annual HCC risk; but unlike other cirrhosis causes, HCC can occasionally occur in NAFLD without cirrhosis). NAFLD also significantly increases cardiovascular mortality — independent of traditional cardiovascular risk factors — cardiovascular disease is the most common cause of death in NAFLD patients overall.

Liver ultrasound is the first-line imaging investigation — detects steatosis when more than 20-30% of hepatocytes are affected; the liver appears bright (hyperechogenic) compared to the kidney; does not reliably detect NASH or fibrosis. Liver enzymes: ALT and AST — elevated in NASH; however, normal ALT does not exclude NASH or even advanced fibrosis. Non-invasive fibrosis assessment tests — to identify patients with advanced fibrosis (who are at risk of cirrhosis and need specialist management) without liver biopsy: FIB-4 index (age x AST / [platelet count x sqrt ALT]) — low score below 1.30 effectively excludes advanced fibrosis (negative predictive value 90%+); high score above 2.67 suggests advanced fibrosis. NAFLD Fibrosis Score (NFS). Enhanced Liver Fibrosis (ELF) score — serum biomarker test (PIIINP, TIMP-1, hyaluronic acid). FibroScan (transient elastography / MR elastography): measures liver stiffness — a surrogate of fibrosis; liver stiffness above 9.2-9.7 kPa suggests advanced fibrosis; above 12-15 kPa suggests cirrhosis; combined with CAP (controlled attenuation parameter) measures hepatic steatosis simultaneously. MRI-PDFF (proton density fat fraction): most accurate non-invasive measure of liver steatosis — useful in clinical trials and monitoring treatment response. Liver biopsy: the gold standard for definitive NASH diagnosis and fibrosis staging (F0-F4) — histology shows: steatosis (fat droplets in hepatocytes), ballooning (hepatocyte injury), lobular inflammation, and fibrosis (Mallory-Denk bodies). Biopsy is reserved for patients where the diagnosis is uncertain, where FIB-4/FibroScan are indeterminate, or for clinical trial entry. Non-invasive serum biomarkers for NASH (Pro-C3, OWLiver): being validated. Hepatocellular carcinoma surveillance: 6-monthly ultrasound in all NASH cirrhosis patients.

Weight loss is the cornerstone of NAFLD/MASLD treatment: even 5% weight loss reduces liver steatosis; 7-10% weight loss can resolve NASH and reduce fibrosis; 10-15%+ weight loss is needed for significant fibrosis regression. Mediterranean diet (high in fibre, olive oil, fish, limited refined carbohydrates and saturated fat) is the most evidence-based dietary pattern for NAFLD — reduces liver fat and improves metabolic parameters independently of weight loss. Reduce or eliminate sugar-sweetened beverages (fructose-rich), ultra-processed foods, and alcohol (even modest alcohol may accelerate NAFLD). Exercise: aerobic exercise (150 minutes/week) reduces liver fat by approximately 3-4% independent of weight loss; resistance training is also beneficial. Coffee consumption (3-4 cups/day) has consistent hepatoprotective associations in NAFLD — reduces fibrosis progression. Pharmacological treatment (for NASH with F2+ fibrosis): Resmetirom (Rezdiffra — thyroid hormone receptor-beta agonist) — the first FDA-approved treatment for NASH with moderate-to-advanced fibrosis (F2-F3) — approved in March 2024. In phase 3 MAESTRO-NASH trial: NASH resolution in 26% (80mg) and 30% (100mg) vs 10% placebo; fibrosis improvement in 24% vs 14%. Administered orally once daily. GLP-1 receptor agonists: semaglutide reduces liver fat, improves NASH histology (NASH resolution in 59% vs 17% placebo in phase 2 CENTAUR trial); phase 3 trials ongoing; available now for weight management and T2DM (NASH benefit as secondary effect). Pioglitazone (PPAR-gamma agonist): reduces NASH activity by 47% vs 19% placebo (Belfort NEJM 2006); causes weight gain; used for NASH with T2DM or prediabetes. Vitamin E (alpha-tocopherol 800 IU/day): reduces NASH activity in non-diabetic, non-cirrhotic adults (PIVENS trial: 43% vs 19% placebo response) but concern about all-cause mortality with high doses; not used in diabetics (increased risk of bladder cancer with pioglitazone, and unclear vitamin E safety). Bariatric surgery: laparoscopic sleeve gastrectomy or Roux-en-Y gastric bypass achieves significant and sustained weight loss leading to NASH resolution in 80-90% and fibrosis regression in 70%+ — considered for NASH patients with BMI above 35 (or 30-35 with metabolic comorbidities). Liver transplantation for decompensated NASH cirrhosis.

Non-alcoholic fatty liver disease (NAFLD) follows a spectrum with distinct complication profiles at each stage. NASH (non-alcoholic steatohepatitis) — the progressive inflammatory form affecting approximately 25% of NAFLD patients — progresses to fibrosis in approximately 40% over 4-6 years, with 10-20% advancing to cirrhosis over 20 years. Cirrhosis from NASH is now the second leading indication for liver transplantation in many high-income countries. NASH cirrhosis carries all the complications of cirrhosis from any cause: portal hypertension, variceal haemorrhage, ascites with spontaneous bacterial peritonitis, hepatic encephalopathy, and hepatorenal syndrome. Hepatocellular carcinoma (HCC) develops in 1-2% of NASH cirrhotic patients annually — increasingly, HCC is also reported in NASH patients without cirrhosis, an unusual pattern contrasting with other aetiologies. Cardiovascular disease is the leading cause of mortality in NAFLD — independent of obesity and metabolic syndrome — due to shared pathophysiology including dyslipidaemia, insulin resistance, systemic inflammation, and oxidative stress; patients with NAFLD have twice the cardiovascular mortality of those without. Type 2 diabetes is both a cause and complication of NAFLD — the relationship is bidirectional, with progressive hepatic steatosis worsening insulin resistance. Advanced fibrosis (F3-F4 on liver biopsy or Fibroscan above 9.0 kPa) significantly increases overall and liver-related mortality risk.

NAFLD is largely a lifestyle-driven disease and is substantially preventable. Maintain a healthy weight: BMI below 25 kg/m² and waist circumference below 80 cm (women) and 94 cm (men) — even modest overweight significantly increases NAFLD risk. Adopt a Mediterranean dietary pattern: high in vegetables, legumes, whole grains, olive oil, nuts, and fish; limited red and processed meat, saturated fat, and refined carbohydrates. Eliminate sugar-sweetened beverages: fructose-containing drinks (sodas, fruit juices, energy drinks) are the single most important dietary driver of liver steatosis. Regular physical activity: 150-300 minutes of moderate aerobic exercise weekly reduces liver fat. Limit alcohol consumption to below 14 units per week (UK guidelines) — MetALD (MASLD plus significant alcohol) is a distinct and more severe entity. Manage metabolic risk factors: optimise blood glucose, blood pressure, and cholesterol — all protect against NAFLD progression. Regular coffee consumption (filtered — not unfiltered boiled coffee which raises cholesterol) has consistent hepatoprotective effects. Annual FBC and LFTs are worthwhile in individuals with obesity, T2DM, or metabolic syndrome to detect early NAFLD when lifestyle intervention is most effective.

Seek emergency care immediately for: vomiting blood (haematemesis) or passing black tarry stools (melaena) — indicates variceal bleeding from cirrhosis and portal hypertension and is immediately life-threatening; sudden onset confusion, drowsiness, or agitation in a patient with known liver disease (hepatic encephalopathy — requires urgent hospital admission and lactulose therapy); and increasing abdominal distension with rapid worsening over days (tense ascites or spontaneous bacterial peritonitis — SBP — a life-threatening complication of cirrhosis). See your doctor for: newly discovered liver enzyme elevation (ALT 2x upper limit of normal or more persisting for more than 3-6 months on repeat testing); right upper quadrant discomfort persisting more than 2 weeks; weight loss combined with fatigue and abnormal liver function; and any individual with T2DM or obesity who has not had liver function tests in over 12 months. Referral to hepatology is recommended for: FIB-4 score above 1.30 (intermediate or high fibrosis risk); FibroScan liver stiffness above 8 kPa; any ultrasound evidence of cirrhosis or portal hypertension; and decompensated liver disease (jaundice, ascites, encephalopathy, varices).