Fatty liver disease
Fatty liver disease (FLD), also known as hepatic steatosis and steatotic liver disease (SLD), 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]
Fatty liver
Hepatic steatosis
Based on the medical history supported by blood tests, medical imaging, liver biopsy[1]
Good if treated early[3]
The main subtypes of fatty liver disease are metabolic dysfunction–associated steatotic liver disease (MASLD, formerly "non-alcoholic fatty liver disease" (NAFLD)) and alcohol-associated liver disease (ALD), with the category "metabolic and alcohol associated liver disease" (metALD) describing an overlap of the two.[5]
The primary risks include alcohol, type 2 diabetes, and obesity.[1][3] 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 nonalcoholic steatohepatitis (NASH), which is associated with poorer outcomes.[1] Diagnosis is based on the medical history supported by blood tests, medical imaging, and occasionally liver biopsy.[1]
Treatment of NAFLD is generally 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 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.[3][6]
Treatment[edit]
Decreasing caloric intake by at least 30% or by approximately 750–1,000 kcal/day results in improvement in hepatic steatosis.[8] For people with NAFLD or NASH, weight loss via a combination of diet and exercise was shown to improve or resolve the disease.[8] 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.[8][15]
Bariatric surgery, while not recommended in 2017 as a treatment for 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.[8][34]
In the case of long-term total-parenteral-nutrition-induced fatty liver disease, choline has been shown to alleviate symptoms.[35][36][37] This may be due to a deficiency in the methionine cycle.[38]
Epidemiology[edit]
NAFLD affects about 30% of people in Western countries and 10% of people in Asia.[2]
In the United States rates are around 35% with about 7% having the severe form NASH.[1] NAFLD affects about 10% of children in the United States.[1] Recently the term Metabolic dysfunction-associated fatty liver disease (MAFLD) has been proposed to replace NAFLD. MAFLD is a more inclusionary diagnostic name as it is based on the detection of fatty liver by histology (biopsy),medical imaging or blood biomarkers but should be accompanied by either overweight/obesity, type 2 diabetes mellitus, or metabolic dysregulation.[39] The new definition no longer excludes alcohol consumption or coexistence of other liver diseases such as viral hepatitis. Using this more inclusive definition, the global prevalence of MAFLD is an astonishingly high 50.7%.[39] Indeed, also using the old NAFLD definition, the disease is observed in up to 80% of obese people, 35% of whom progress to NASH,[40] and in up to 20% of normal weight people,[10] despite no evidence of excessive alcohol consumption. FLD is the most common cause of abnormal liver function tests in the United States.[14] Fatty liver is more prevalent in Hispanic people than white, with black people having the lowest prevalence.[10]
In the study Children of the 90s, 2.5% born in 1991 and 1992 were found by ultrasound at the age of 18 to have non-alcoholic fatty liver disease; five years later transient elastography found over 20% to have the fatty deposits on the liver, indicating non-alcoholic fatty liver disease; half of those were classified as severe. The scans also found that 2.4% had a degree of liver fibrosis, which can lead to cirrhosis.[41][42]
After the lockdown of the COVID-19 pandemic, a study demonstrated that 48% of patients with liver steatosis gained weight, while 16% had a worsened steatosis grade. Weight gain was associated with poor adherence to the suggested diet, reduced levels of physical activity, and increased prevalence of homozygosity for the PNPLA3 rs738409 single nucleotide polymorphism.[43] PNPLA3 rs738409 is already a known risk factor for NAFLD.[44][45]
In animals[edit]
Fatty liver disease can occur in pets such as reptiles (particularly turtles[46]) and birds[47] as well as mammals like cats and dogs.[48] The most common cause is overnutrition. A distinct sign in birds is a misshapen beak. Fatty livers can be induced via gavage in geese or ducks to produce foie gras. Fatty liver can also be induced in ruminants such as sheep by a high-caloric diet.[49][50]