Fatty Liver Disease: Symptoms, Causes, and Treatment Methods

What Is Fatty Liver Disease?

Hello, I am Dr. Emre Gecer. Fatty liver disease, called hepatosteatosis in medical terminology, is the abnormal accumulation of fat (triglycerides) within liver cells (hepatocytes). In a normal liver, fat accounts for less than 5% of liver weight; exceeding this is defined as fatty liver disease. The diagnostic criterion is the presence of fat droplets in more than 5% of liver cells on imaging or biopsy.

Fatty liver disease is divided into two main groups: alcoholic and non-alcoholic. In this article we will mainly focus on non-alcoholic fatty liver disease (NAFLD). In current medical literature the term MASLD (Metabolic Dysfunction-Associated Steatotic Liver Disease) is increasingly used in place of NAFLD; this new name emphasizes the metabolic basis of the disease.

How Common Is Fatty Liver Disease?

Fatty liver disease is today the most common chronic liver disease worldwide. It is estimated to affect approximately 25-30% of the global adult population. Studies in Turkey report rates between 20-30%. Prevalence rises to 60-80% in obese individuals and 50-70% in patients with type 2 diabetes. Worryingly, with the rise of childhood obesity it is increasingly seen in children as well.

Stages of Fatty Liver Disease: The NAFLD Spectrum

Fatty liver disease is not a single disease but a broad disease spectrum, and is evaluated in four stages:

• Simple steatosis: Fat accumulates in liver cells but there is no significant inflammation or damage. The vast majority of patients (around 80%) are at this stage. The good news is that this stage usually has a benign course and is reversible.
• NASH (Non-Alcoholic Steatohepatitis): In addition to steatosis, inflammation and hepatocyte injury (ballooning degeneration) develop in the liver. Approximately 20-30% of NAFLD patients develop NASH. NASH is the progressive form of the disease and can advance to fibrosis.
• Fibrosis: Chronic inflammation leads to the formation of scar tissue (fibrosis) in the liver. Fibrosis is graded from F0 (no fibrosis) to F4 (cirrhosis). F3 and F4 are considered advanced fibrosis.
• Cirrhosis: The result of advanced fibrosis is complete disruption of liver architecture. Liver failure, portal hypertension and the risk of hepatocellular carcinoma (liver cancer) rise sharply at this stage. The rapid rise of NASH cirrhosis among indications for liver transplantation is a major public health concern.

Causes and Risk Factors of Fatty Liver Disease

Metabolic Risk Factors

Fatty liver disease is essentially a metabolic disease and has a strong association with the components of metabolic syndrome:

• Obesity: The strongest risk factor. Abdominal (visceral) obesity in particular is directly linked to fatty liver disease. A waist circumference greater than 102 cm in men or 88 cm in women increases the risk. However, fatty liver disease can also be seen in 10-20% of normal-weight individuals (lean NAFLD).
• Insulin resistance and type 2 diabetes: Insulin resistance is the most central mechanism in the pathogenesis of fatty liver disease. Type 2 diabetes both increases the risk of NAFLD and leads to a more aggressive disease course.
• Dyslipidemia: High triglycerides and low HDL cholesterol are frequently found together with fatty liver disease.
• Metabolic syndrome: When the above factors coexist as metabolic syndrome, NAFLD prevalence rises above 80%.

Other Risk Factors

• Genetic predisposition: The PNPLA3 gene (rs738409 variant) significantly increases the risk of fatty liver disease and NASH. The TM6SF2 gene is another important genetic marker.
• Diet: High fructose intake (especially sugary drinks), refined carbohydrates and a diet rich in saturated fat
• Sedentary lifestyle
• Certain medications: Amiodarone, methotrexate, tamoxifen, corticosteroids, valproic acid
• Endocrine disorders: Hypothyroidism, polycystic ovary syndrome (PCOS), hypogonadism
• Rapid weight loss and starvation: Paradoxically, very rapid weight loss can also trigger fatty liver disease

Pathophysiology: The Two-Hit Hypothesis

The classical model explaining the progression of fatty liver disease to NASH is the "two-hit hypothesis":

• First hit: Excess fat accumulation in the liver (steatosis) due to insulin resistance. Insulin resistance increases the release of free fatty acids from adipose tissue, stimulates de novo lipogenesis (new fat synthesis) in the liver, and reduces beta-oxidation of fatty acids.
• Second hit: Oxidative stress, lipid peroxidation, inflammatory cytokines (TNF-alpha, IL-6), endoplasmic reticulum stress and mitochondrial dysfunction lead to hepatocyte injury and inflammation (steatohepatitis).

Today this model has been extended into the "multiple parallel hits" model. Changes in the gut microbiota, adipokines, and genetic and epigenetic factors all play simultaneous roles in disease progression.

Symptoms of Fatty Liver Disease

The most important feature of fatty liver disease is that it usually runs a silent course. Most patients have no symptoms at all, and the diagnosis is often made incidentally during tests done for other reasons. However, some patients may experience the following symptoms:

• Fatigue and weakness: The most commonly reported symptom, seen in 50-75% of patients
• Right upper quadrant pain or discomfort: A dull pain or sense of fullness due to stretching of the liver capsule from hepatomegaly
• Abdominal bloating
• Loss of appetite

In advanced stages (once cirrhosis develops), serious findings such as jaundice (yellowing of the skin and eyes), abdominal fluid accumulation (ascites), leg edema, easy bruising, itching and altered mental status (hepatic encephalopathy) may appear.

Important warning: The absence of symptoms does not mean the disease is mild. Advanced fibrosis and even cirrhosis can remain asymptomatic for a long time. For this reason, screening is important in individuals with risk factors.

Diagnostic Methods

Laboratory Tests

• Liver enzymes (ALT, AST): May be mildly to moderately elevated; however, normal liver enzymes do not exclude NAFLD or NASH. ALT is usually higher than AST (AST/ALT ratio <1); this ratio reverses as cirrhosis develops.
• GGT and ALP: May be mildly elevated
• Metabolic panel: Fasting glucose, HbA1c, lipid profile, insulin level (HOMA-IR calculation)
• Exclusion of other liver diseases: Hepatitis B and C serology, autoimmune markers, iron studies, ceruloplasmin

Imaging Methods

• Ultrasonography (US): The first-line diagnostic tool. Fatty liver appears as increased echogenicity (bright liver) on ultrasound. Its advantages are that it is inexpensive, easily accessible and non-invasive. However, it may not detect steatosis below 30% and provides limited information about fibrosis.
• FibroScan (transient elastography): A non-invasive method that measures liver stiffness (degree of fibrosis) and the amount of steatosis (CAP score). It is extremely valuable for following fibrosis. It is measured in kPa; high values indicate advanced fibrosis.
• MRI-PDFF (Proton Density Fat Fraction): The most accurate method for measuring liver fat content. It is accepted as the gold standard in clinical research.

Non-Invasive Fibrosis Scores

• FIB-4 score: Calculated using age, AST, ALT and platelet count. A score <1.30 is considered low risk and >2.67 high risk. It is the most widely used screening tool in clinical practice.
• NAFLD Fibrosis Score (NFS): Uses age, BMI, presence of diabetes, AST/ALT ratio, platelet count and albumin.

Liver Biopsy

Liver biopsy is still the gold standard for diagnosing NASH and staging fibrosis. However, because it is invasive and carries risks of sampling error and complications, it is not used in every patient. It is generally preferred in cases of diagnostic uncertainty, suspected advanced fibrosis, or in clinical studies.

Treatment Approaches

Lifestyle Changes: The Cornerstone of Treatment

Lifestyle changes are the most effective and best-proven treatment for fatty liver disease:

• Weight loss: The most critical component of treatment. A loss of 7-10% of body weight markedly reduces steatosis, can resolve NASH and even reverse fibrosis. A 3-5% weight loss improves steatosis, 7-10% improves inflammation and ballooning, and more than 10% improves fibrosis. Weight loss should be gradual, at 0.5-1 kg per week; very rapid weight loss should be avoided.
• Diet: The Mediterranean diet is the dietary pattern with the strongest evidence in NAFLD treatment. It is rich in olive oil, fish, vegetables and fruit, nuts, and whole grains, and low in red meat, processed food and sugar. Fructose (especially drinks containing high-fructose corn syrup) directly increases liver fat and must be strictly limited.
• Exercise: At least 150-200 minutes per week of moderate-intensity aerobic exercise (brisk walking, swimming, cycling) is recommended. Exercise reduces liver fat independently of weight loss and improves insulin resistance. Adding resistance (strength) exercise provides additional benefit.
• Alcohol restriction: In NAFLD patients, alcohol consumption accelerates liver damage. In the presence of advanced fibrosis or cirrhosis, alcohol should be stopped completely.

Pharmacological Treatment

As of 2024, there is no FDA-approved medication specific to NAFLD/NASH, but some agents have shown promising results:

• Pioglitazone: An insulin sensitizer. It reduces steatosis, inflammation and ballooning in both diabetic and non-diabetic NASH patients. Side effects include weight gain and loss of bone density.
• Vitamin E (800 IU/day): Shown to provide histological improvement in non-diabetic adult NASH patients (PIVENS study). However, there is concern that long-term high-dose vitamin E may increase the risk of prostate cancer.
• GLP-1 receptor agonists: Drugs such as semaglutide and liraglutide produce weight loss and show favorable effects on fatty liver and NASH. They are particularly promising in obese and diabetic NASH patients.
• Resmetirom (Rezdiffra): A thyroid hormone receptor beta agonist approved in 2024 for the treatment of NASH-related fibrosis. It is the first specific drug approved in this area.

Alcoholic Fatty Liver Disease

Alcoholic Fatty Liver Disease (AFLD) develops as a result of excessive alcohol consumption. Daily intake of more than 30 g of alcohol in men and more than 20 g in women constitutes a risk. Unlike NAFLD, complete cessation of alcohol is the essential treatment. In the early stage, stopping alcohol can fully reverse the steatosis. In advanced stages, alcoholic hepatitis and cirrhosis may develop.

Follow-Up in Fatty Liver Disease

Regular follow-up of patients diagnosed with fatty liver disease is important:

• Low-risk patients (simple steatosis, FIB-4 <1.30): Annual follow-up of liver enzymes and FIB-4 score
• Intermediate-risk patients (indeterminate FIB-4): Assessment with FibroScan or further investigations
• High-risk patients (advanced fibrosis/cirrhosis): Gastroenterology/hepatology follow-up, hepatocellular carcinoma screening (ultrasound and alpha-fetoprotein every 6 months), assessment for portal hypertension

Conclusion

Fatty liver disease is a silent but potentially serious condition. Its prevalence is rising rapidly alongside the epidemic of obesity, diabetes and metabolic syndrome. With early diagnosis and lifestyle changes, the disease can be reversed. Weight loss, a Mediterranean diet and regular exercise form the basis of treatment. If you have risk factors, I recommend that you have regular health check-ups and do not neglect your liver health.

Wishing you healthy days.
Dr. Emre Gecer

References

• Harrison's Principles of Internal Medicine, 22nd Edition — Chapters: Fatty Liver Disease
• Sleisenger and Fordtran's Gastrointestinal and Liver Disease, 11th Edition — Chapter: Nonalcoholic Fatty Liver Disease
• EASL–EASD–EASO Clinical Practice Guidelines for the Management of NAFLD, 2016
• AASLD Practice Guidance on the Clinical Assessment and Management of NAFLD, 2023