Fatty liver disease (FLD), also known as hepatic steatosis, is a condition where excess fat builds up in the liver.[1] Often there are no or few symptoms.[1][2] Occasionally there may be tiredness or pain in the upper right side of the abdomen.[1] Complications may include cirrhosis, liver cancer, and esophageal varices.[1][3]

There are two types of fatty liver disease non-alcoholic fatty liver disease (NAFLD) and alcoholic liver disease.[1] NAFLD is made up of simple fatty liver and non-alcoholic steatohepatitis (NASH).[5][1] The primary risks include alcohol, type 2 diabetes, and obesity.[3][1] Other risk factors include certain medications such as glucocorticoids, and hepatitis C.[1] It is unclear why some people with NAFLD develop simple fatty liver and others develop NASH.[1] Diagnosis is based on the medical history supported by blood tests, medical imaging, and occasionally liver biopsy.[1]

It is recommended that people with fatty liver disease do not drink alcohol.[3][2] Treatment of NAFLD is generally otherwise by dietary changes and exercise to bring about weight loss.[1] In those who are severely affected, liver transplantation may be an option.[1] More than 90% of all heavy drinkers develop fatty liver while about 25% develop the more severe alcoholic hepatitis.[4] NAFLD affects about 30% of people in Western countries and 10% of people in Asia.[2] NAFLD affects about 10% of children in the United States.[1] It occurs more often in older people and males.[5][3]

Signs and symptoms

Often there are no or few symptoms.[1] Occasionally there may be tiredness or pain in the upper right side of the abdomen.[1]

Complications

Fatty liver can develop into a fibrosis or a liver cancer.[6] For people affected by NAFLD, the 10-year survival rate was about 80%. The rate of progression of fibrosis in NASH is estimated to one per 7 years and 14 years for NAFLD, with an increasing speed.[7][8] There is a strong relationship between these pathologies and metabolic illnesses (diabetes type II, metabolic syndrome). These pathologies can also affect non-obese people, who are then at a higher risk.[6]

Less than 10% of people with cirrhotic alcoholic FLD will develop hepatocellular carcinoma,[9] the most common type of primary liver cancer in adults, but up to 45% people with NASH without cirrhosis can develop hepatocellular carcinoma.[10]

The condition is also associated with other diseases that influence fat metabolism.[11]

Causes

Fatty liver (FL) is commonly associated with metabolic syndrome (diabetes, hypertension, obesity, and dyslipidemia), but can also be due to any one of many causes:[12][13]

Alcohol

Alcoholism is one of the causes of fatty liver due to production of toxic metabolites like aldehydes during metabolism of alcohol in the liver. This phenomenon most commonly occurs with chronic alcoholism.

Metabolic

abetalipoproteinemia, glycogen storage diseases, Weber–Christian disease, acute fatty liver of pregnancy, lipodystrophy

Nutritional

obesity, malnutrition, total parenteral nutrition, severe weight loss, refeeding syndrome, jejunoileal bypass, gastric bypass, jejunal diverticulosis with bacterial overgrowth

Drugs and toxins

amiodarone, methotrexate, diltiazem, expired tetracycline, highly active antiretroviral therapy, glucocorticoids, tamoxifen,[14] environmental hepatotoxins (e.g., phosphorus, mushroom poisoning)

Other

celiac disease,[15] inflammatory bowel disease, HIV, hepatitis C (especially genotype 3), and alpha 1-antitrypsin deficiency[16]

Treatment

Decreasing caloric intake by at least 30% or by approximately 750–1,000 kcal/day results in improvement in hepatic steatosis. [6] For people with NAFLD or NASH, weight loss via a combination of diet and exercise was shown to improve or resolve the disease.[6] In more serious cases, medications that decrease insulin resistance, hyperlipidemia, and those that induce weight loss such as bariatric surgery as well as Vitamin E have been shown to improve or resolve liver function.[6][13]

Bariatric surgery, while not recommended in 2017 as a treatment for fatty liver disease (FLD) alone, has been shown to revert FLD, NAFLD, NASH and advanced steatohepatitis in over 90% of people who have undergone this surgery for the treatment of obesity.[6][27]

In the case of long-term total parenteral nutrition induced fatty liver disease, choline has been shown to alleviate symptoms.[28][29][30] This may be due to a deficiency in the methionine cycle.[31]