Non-alcoholic fatty liver disease (NAFLD) is a condition marked by the accumulation of excess fat within liver cells that is not caused by heavy alcohol consumption. Its occurrence has risen dramatically, and it is now a widespread chronic liver condition. Recent estimates suggest a global prevalence of approximately 32% among adults, while in the United States, about a quarter of the population has NAFLD. The disease has also become more common in children, with its prevalence more than doubling over the last two decades.
Underlying Causes and Associated Conditions
The development of NAFLD is closely linked with metabolic syndrome, a cluster of conditions including high blood pressure, high blood sugar, and abnormal cholesterol or triglyceride levels. A primary factor in its onset is insulin resistance, a state where the body’s cells do not respond effectively to insulin. This resistance promotes the storage of fat in the liver, a process known as steatosis.
Obesity, particularly abdominal fat concentrated around the waist, is a significant contributor. This type of fat is metabolically active and releases substances that can promote inflammation and insulin resistance. The presence of type 2 diabetes or prediabetes, both characterized by high blood sugar, further increases the likelihood of developing a fatty liver.
While metabolic factors are the main drivers, genetics can also influence susceptibility. Certain genetic variations can make some individuals more prone to storing liver fat and developing subsequent damage than others.
Symptoms and Diagnosis
NAFLD is a “silent” disease that causes no noticeable symptoms in its initial stages. When symptoms do appear, they are non-specific and can include persistent fatigue, a feeling of being unwell, or a dull, aching discomfort in the upper right abdomen where the liver is located.
The first indication often comes from routine blood tests showing elevated liver enzymes, such as alanine aminotransferase (ALT) and aspartate aminotransferase (AST). While these results suggest liver inflammation or cell injury, enzyme levels can be normal in some people with NAFLD, making the tests not definitive on their own.
To confirm fat in the liver, imaging studies are employed. An ultrasound is a common first step, while computed tomography (CT) scans or magnetic resonance imaging (MRI) can provide more detailed pictures and quantify the amount of fat. A specialized ultrasound-based test called transient elastography (FibroScan) measures liver stiffness to assess scarring, or fibrosis.
A liver biopsy, where a small tissue sample is examined, is the most accurate method for diagnosing NAFLD and its severity, but it is an invasive procedure that is not always required.
The Spectrum of NAFLD
NAFLD exists on a spectrum with two main types: non-alcoholic fatty liver (NAFL) and non-alcoholic steatohepatitis (NASH). The distinction is important for understanding the potential progression of the disease.
The most common form is NAFL, characterized by the presence of fat in the liver (steatosis) with little to no accompanying inflammation or liver cell damage. For many individuals, the condition does not advance beyond this stage, and the liver can still function normally without leading to long-term complications if managed.
A smaller subset of people with NAFLD develop the more aggressive form, non-alcoholic steatohepatitis (NASH). NASH involves fat accumulation plus significant inflammation and injury to liver cells. This ongoing inflammation can trigger the formation of scar tissue (fibrosis), which can progress to cirrhosis—a late-stage condition where the liver is severely scarred and its structure is permanently damaged. Cirrhosis impairs liver function and increases the risk of developing liver cancer (hepatocellular carcinoma).
Managing NAFLD Through Lifestyle
Currently, there are no medications specifically approved for NAFLD, making lifestyle modifications the foundation of its management. These changes can help reduce liver fat, decrease inflammation, and in some cases, even reverse the course of the disease, particularly in its earlier stages.
Weight loss is one of the most effective strategies. Research shows that a reduction of 5-10% of total body weight can significantly decrease fat in the liver and reduce the inflammation associated with NASH. This weight loss should be achieved gradually through a combination of dietary changes and physical activity.
Adopting a healthier eating pattern, such as the Mediterranean diet, is another component of management. This involves consuming fruits, vegetables, whole grains, lean proteins, and healthy fats while limiting processed foods, sugary drinks, and foods high in saturated and trans fats. Reducing the consumption of fructose, a type of sugar found in many sweetened beverages and snacks, is particularly beneficial.
Regular physical activity is also recommended to help with weight management and improve insulin sensitivity. A combination of aerobic exercise (brisk walking, cycling, or swimming) and resistance training is advised. The goal is to incorporate activity into most days of the week to support overall metabolic health and reduce liver fat.