Nonalcoholic fatty liver disease (NAFLD) is a global health concern, characterized by excessive fat accumulation within liver cells. This condition is distinct from liver damage caused by heavy alcohol consumption. Its increasing prevalence is closely linked to rising rates of obesity and metabolic disorders worldwide. NAFLD is one of the most common causes of liver disease in the United States, affecting an estimated 24% of adults.
What is Nonalcoholic Fatty Liver Disease?
NAFLD signifies a liver containing over 5% fat by weight, a condition called steatosis. The “nonalcoholic” descriptor clarifies that fat buildup is not due to significant alcohol intake (typically over 2 standard drinks per day for men or 1 for women). Instead, it arises from metabolic factors affecting how the body processes fats and sugars.
NAFLD includes two primary forms: simple fatty liver (steatosis) and nonalcoholic steatohepatitis (NASH). Simple fatty liver involves fat accumulation without significant inflammation or liver cell damage, and generally does not progress to severe injury. NASH is a more serious condition where fat is accompanied by inflammation and liver cell damage, potentially leading to scarring.
The development of NAFLD is strongly associated with metabolic syndrome, a cluster of conditions including obesity, insulin resistance, type 2 diabetes, high cholesterol, and high triglycerides. Insulin resistance, where cells do not respond effectively to insulin, plays a central role by contributing to increased fat accumulation in the liver. Genetic factors are also thought to play a role in why some individuals with NAFLD develop NASH.
Identifying NAFLD
NAFLD often presents without noticeable symptoms in its early stages, earning it the label of a “silent” disease. It is frequently detected incidentally during routine medical evaluations. A common initial indication might be elevated levels of liver enzymes, such as alanine aminotransferase (ALT) and aspartate aminotransferase (AST), discovered during standard blood tests.
Imaging tests, such as abdominal ultrasound, are often the first diagnostic tools when liver issues are suspected. These scans can reveal fat in the liver, though they cannot distinguish between simple fatty liver and NASH, or assess inflammation or scarring. More advanced imaging techniques, including magnetic resonance imaging (MRI) or computed tomography (CT) scans, offer greater detail and can identify mild liver fibrosis. Specialized ultrasound methods like transient elastography (FibroScan) or magnetic resonance elastography (MRE) also measure liver stiffness, indicating fibrosis presence and severity.
A liver biopsy remains the most definitive method for diagnosing NASH and assessing liver damage, including inflammation and scarring. This procedure involves taking a small tissue sample from the liver for microscopic examination. Doctors may also use blood test results to calculate scores, such as FIB-4 or APRI, which help identify the likelihood of advanced liver fibrosis.
How NAFLD Progresses
NAFLD progression typically begins with simple fatty liver (steatosis), where fat accumulates in liver cells without significant inflammation or damage. This initial stage is generally benign and often does not lead to severe liver problems, though it can advance for some.
The next stage is nonalcoholic steatohepatitis (NASH), where fat is accompanied by inflammation and liver cell damage. This inflammation can cause ongoing injury. Approximately 20% of individuals with metabolic dysfunction-associated steatotic liver disease (MASLD), the updated term for NAFLD, develop NASH.
Persistent inflammation in NASH can lead to fibrosis, the formation of scar tissue in the liver. As the liver attempts to repair itself, collagen fibers are deposited, stiffening it. If inflammation continues, fibrosis can spread. The most severe stage is cirrhosis, occurring after years of chronic inflammation and scarring. In cirrhosis, the liver becomes significantly scarred, hardened, and loses its ability to function properly. This damage is permanent.
Cirrhosis can lead to serious complications, including liver failure, where the liver can no longer perform its vital functions. Symptoms include fluid buildup in the abdomen (ascites), leg swelling, and confusion. Cirrhosis also significantly increases the risk of developing liver cancer, specifically hepatocellular carcinoma. While liver-related complications are a concern, cardiovascular disease is the leading cause of death in people with MASLD.
Lifestyle and Medical Management
Managing NAFLD primarily relies on adopting comprehensive lifestyle changes, considered the most effective approach. Gradual weight loss is a primary treatment, as even a modest reduction in body weight significantly improves liver health. Losing just 3% to 5% of initial body weight can offer benefits, while a loss of 10% or more can help remove fat from the liver and improve NASH.
Dietary modifications are also highly recommended. Adopting a healthy eating pattern, such as one similar to the Mediterranean diet, is beneficial. This typically involves reducing refined carbohydrates, sugary drinks, and unhealthy fats, while increasing fruits, vegetables, whole grains, and lean proteins. Limiting ultra-processed foods, often high in saturated fats and sugars, is also advised.
Increasing physical activity is another important component. Regular exercise can independently reduce liver fat, prevent fibrosis, and lower overall mortality risk. Aim for at least 150 minutes of moderate-intensity activity per week, such as brisk walking or cycling. All types of exercise can contribute to improving NAFLD, even without significant weight loss.
Managing co-existing medical conditions is equally important. Individuals with NAFLD frequently have other health issues like type 2 diabetes, high cholesterol, and high blood pressure, which can worsen liver damage. Closely managing these conditions through diet, exercise, and prescribed medications is an integral part of NAFLD management. While lifestyle changes are the primary focus, a new medication, resmetirom (Rezdiffra), has recently been approved to treat NASH with moderate to severe liver scarring by reducing liver fat. For most, medication is supplementary to consistent lifestyle adjustments.