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Non-Alcoholic Fatty Liver Disease

What Obesity, Diabetes and Other Conditions Can Do To Your Liver


Updated June 05, 2014

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Non-Alcoholic Fatty Liver Disease

Obesity can harm your liver

Steven Puetzer / Getty Images

A form of liver disease is on the rise in North America, and this one has nothing to do with drinking to excess. It’s called Non-Alcoholic Fatty Liver Disease, or NAFLD, and researchers are dismayed at the rate at which it’s growing, thanks to a huge increase in obesity rates over the last three decades. At the extreme end, non-alcoholic fatty liver disease can lead to liver failure and death. The chances of its progressing increase with age. Here's what you should know about the causes of fatty liver disease.

What your liver does: The role of the liver — the largest internal organ within the human body — is complex and varied. Hundreds of functions are performed by the liver, ranging from processing everything we eat and drink, pulling toxins from our blood, fighting off infection, controlling blood sugar levels, and helping to manufacture the hormones and proteins we need to survive.

The recent history of fatty liver disease: Officially recognized as a disease only in the early 1980s, the condition had perplexed physicians for some time. Obese and diabetic patients were also found to have certain elevated liver enzymes and enlarged livers. Though these symptoms are virtually identical to those typically seen in alcoholics, most of these patients insisted they were not drinking to excess.

In 1980, a team of researchers first described their observations at the Mayo Clinic in Rochester, NY, in the journal Mayo Clinic Proceedings. Since then, many scientists have chronicled the damage caused by NAFLD.

Fat and the liver: While it is normal and healthy to have some fat in the liver, too much fat can cause serious problems. The liver normally weighs about three pounds, or 1.4 kg. If more than 5-10% of the liver’s weight is fat, it is considered by scientists and doctors to be a “fatty liver.” In many people, excess liver fat, or steatosis, causes no problems — but it does leave the liver more vulnerable to serious damage like inflammation and scarring.

Though the exact effect of excess fat on the liver isn’t well understood, it appears to create problems on a spectrum. At the low and least harmful end, the liver may be able to perform its many functions even while it contains too much fat. However, once inflammation and swelling occur in the organ, scarring can result as the liver tries to heal itself. This is a hallmark symptom of liver injury in advanced non-alcoholic fatty liver disease: collagen is laid down, and fibrosis or thickening of the liver tissue ensues. As the disease progresses, about 10% of cases will develop over the next ten years into the much more serious NASH, or non-alcoholic steatohepatitis. NASH can lead to cirrhosis or hardening of the liver, liver failure, liver cancer, and death.

Symptoms and Diagnosis: Often people have no symptoms of fatty liver disease. In more advanced stages, however, it may cause fatigue, nausea, abdominal pain and yellowing skin or eyes (as in jaundice), which are all signs of impaired liver function. It's usually diagnosed with tests that detect elevated liver enzymes, or an ultrasound that determines whether the liver is enlarged. A liver biopsy is required to determine whether a person has NASH, or simple fatty liver.

Who gets non-alcoholic fatty liver disease? Though the exact causes of NAFLD are not known, most of the people who develop it are obese, have type 2 diabetes or have metabolic syndrome, which is associated with insulin resistance. What’s more, the severity of NAFLD increases with the degree of obesity, and abdominal or belly fat seems to increase the risk of dangerous NASH, even in patients with a body mass index (BMI) in a normal range.

In industrialized countries, 20-40% of the general population is believed to have some form of fatty liver disease. About 10-20% of those will go on to develop NASH within a period of ten years. According to Mariana Lazo, assistant professor of Medicine and Epidemiology at Johns Hopkins University School of Medicine in Baltimore, MD, fatty liver now ranks as the second-leading cause requiring a liver transplant, after infection with the hepatitis virus.



NAFLD and diet: While obesity and diabetes are risk factors for fatty liver disease, the exact role that nutrition plays is not well understood. It’s believed that too much fat in the diet, or problems metabolizing it, are largely to blame.

Changes in liver enzymes may happen quickly. In the 2004 documentary Super Size Me, director Morgan Spurlock set out to track the effects of eating nothing but McDonald’s fast food three meals a day, for thirty days. Spurlock had a team of doctors — including a cardiologist, a gastroenterologist, and an internist — monitor him before, during, and after his personal gastric odyssey. At the start, they predicted his triglyceride and cholesterol levels would most likely increase, and that his liver would probably be able to metabolize the additional fats from his month-long binge. Less than two-thirds of the way through his project, however, Spurlock’s liver enzymes had increased more than ten-fold, a jump that shocked his internist. The physician observed that he’d never heard of such rapid decline in liver function induced by a high-fat diet.

Super Size Me is no large-scale clinical trial, but it offers insight into the potential effects of a highly-processed and high-fat diet on the liver. Since no such eating plan could ethically be prescribed for a group of study subjects, it will be tough for researchers to determine the exact course of non-alcoholic fatty liver disease. Until there are more answers — and without any medical therapy such as drugs or vaccines currently available — prevention and treatment remain the same: eat a nutritious, anti-aging diet, maintain a healthy weight by eating the right number of daily calories, control diabetes if you have it, and get regular exercise.

It’s not just your heart that will thank you.


Angulo, Paul, and Lindor, Keith. Non-alcoholic Fatty Liver Disease. Journal of Gastroenterology and Hepatology (2002) 17 (Suppl.) S186–S190.

Fatty Liver Disease. Canadian Liver Foundation Public Information Sheet. Accessed December 10, 2012.

Lazo M, Hernaez R, Bonekamp S, Kamel IR, Brancati FL, Guallar E, Clark JM. “Non-alcoholic fatty liver disease and mortality among US adults: prospective cohort study.” BMJ. 2011 Nov 18;343:d6891.

Ludwig J, Viggiano TR, McGill DB, Oh BJ. Nonalcoholic steatohepatitis: Mayo Clinic experiences with a hitherto unnamed disease. Mayo Clin Proc 1980; 55:434-8.

Non-alcoholic Fatty Liver Disease (NAFLD). American Liver Foundation Public Information Sheet. Accessed December 10, 2012.

Nonalcoholic Steatohepatitis. US Department of Health and Human Services Public Information Sheet. Accessed December 7, 2012.

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