About 30% to 40% of American adults have a condition that has no visible signs and rarely causes symptoms, but can raise the risk of heart disease, diabetes, cirrhosis and liver cancer. It’s called nonalcoholic fatty liver disease—and as American waistlines continue to expand, the prevalence of this dangerous condition is growing as well.
Nonalcoholic fatty liver disease, or NAFLD, is an umbrella term for several stages of disease. Most people with NAFLD have what’s known as simple fatty liver, which means that more than 5% of the liver is made up of fat cells. (Fat in the liver can also be a product of heavy alcohol use, which is known as alcoholic fatty liver disease.)
Like fat accumulation in the rest of the body, this condition is often related to obesity, poor diet and sedentary lifestyle. Excess weight also seems to make genetic risk factors worse: A recent study published in Nature Genetics found that people with a high-risk variant of the PNPLA3 gene were much more likely to have fatty liver disease if they were obese than if they were thin.
“If you are obese and lack the variant, then there is a good chance that you won’t have excess fat in your liver,” says study co-author Jonathan Cohen, professor of internal medicine at UT Southwestern Medical Center. “But if you are obese and do have the variant—particularly if you have two copies of the variant—you are very likely to have excess fat in your liver.”
People with simple fatty liver don’t have inflammation or scarring in their liver and don’t appear to be at high risk for liver complications. But the condition affects insulin sensitivity and puts people at higher risk for diabetes and cardiovascular disease. “Increased liver fat is never normal,” says Dr. Jaideep Behari, associate professor and founder of the University of Pittsburgh Medical Center’s Fatty Liver Clinic.
An advanced form of NAFLD, called nonalcoholic steatohepatitis, or NASH, affects 3% to 12% of U.S. adults. “This form is characterized by inflammation and cell injury,” says Behari. “Cells are dying and there’s progressive scarring, which can lead to cirrhosis and even liver cancer.”
Scientists aren’t sure why some people with simple fatty liver go on to develop NASH while other don’t; research suggests that people with diabetes, high blood pressure, high cholesterol and excess fat around their middle are all at higher risk. Behari says that some people even alternate between the two forms of the disease.
“Sometimes people exercise more and eat a healthier diet while at other times they’re being less healthy,” he says. “They’re going back and forth with their lifestyle, and the condition of their liver is going back and forth as well.”
While fatty liver is much more common in people who are overweight and obese, Behari says doctors have also seen an increase in people with normal body weight, as well—what’s known as lean fatty liver. Fatty liver also tends to affect certain groups of people who tend to have lower BMIs than typical Western populations, like people of Asian descent.
Most cases of NAFLD have no symptoms. They may be diagnosed if elevated liver enzymes are noted during a routine blood test, or if a fatty liver is discovered during an unrelated CT scan, ultrasound or surgical procedure. Despite the rising rates and known health risks of fatty liver disease, there are currently no official recommendations for routine screening.
“I think there’s a real gap between the prevalence of the disorder and how we are diagnosing and counseling our patients,” says Behari, who says he hopes clinical guidelines will be revised in the next few years.
Still, Behari advises patients who have been told in the past that they have fatty liver to ask their doctor to take a closer look, either with a blood test or imaging scans. “I see at least one or two patients a week with advanced cases who were told at some point in the past not to worry about it,” he says. “With everything we know about fatty liver in 2017, I don’t think that’s still something we can tell our patients.”
There are no drugs approved to treat fatty liver disease, although losing weight through diet and exercise can help reduce fat in the liver and related inflammation. Doctors can also help patients identify other obstacles to weight loss, like sleep problems or certain medications.
“For the majority of patients, lifestyle modification is way more effective than any drug,” says Behari. “All of these chronic disorders—fatty liver, diabetes, heart disease—share an underlying metabolic component, and the same common-sense healthy living principles apply for all of them.”