Most people know that consumption of fast food can lead to an array of health issues, such as heart disease or diabetes. Now a new study from Keck Medicine of University of Southern California has found a link between eating fast food and non-alcoholic fatty liver disease (NAFLD).

Published in Clinical Gastroenterology and Hepatology, the study defined fast food as meals from a drive-through restaurant or a restaurant without waitstaff. Researchers found that people with diabetes or obesity who receive 20% or more of their daily caloric intake from fast food have “severely elevated” levels of fat in their liver compared with people who consume little to no fast food, according to a Keck Medicine news release.

“Healthy livers contain a small amount of fat, usually less than 5%, and even a moderate increase in fat can lead to non-alcoholic fatty liver disease,” said Keck hepatologist Ani Kardashian, MD, the lead author of the study, in the news release. “The severe rise in liver fat in those with obesity or diabetes is especially striking and probably due to the fact that these conditions cause a greater susceptibility for fat to build up in the liver.”

NAFLD and its more severe form, non-alcoholic steatohepatitis (NASH), are responsible for a growing proportion of advanced liver disease, mirroring a global rise in obesity. Fatty  liver disease can lead to liver fibrosis, cirrhosis and even liver cancer. With no effective approved medical therapies, management depends on lifestyle changes such as weight loss and exercise.

This is one of the first studies to demonstrate the negative impact of fast food on liver health, according to Kardashian. Even small portions of fast food, which contains high amounts of carbohydrates and fat, can cause damage to the liver.

“If people eat one meal a day at a fast food restaurant, they may think they aren’t doing harm,” Kardashian said. “However, if that one meal equals at least one fifth of their daily calories, they are putting their livers at risk.”

Researchers used the most recent data from the 2017 to 2018 National Health and Nutrition Examination Survey to observe how fast food impacts NAFLD. They evaluated the fatty liver measurement of about 4,000 adults and found that 52% consumed some fast food. Of this group, 29% consumed one fifth or more daily calories from fast food and each person experienced a rise in liver fat levels.

“Our findings are particularly alarming as fast food consumption has gone up in the last 50 years, regardless of socioeconomic status,” Kardashian said. “We’ve also seen a substantial surge in fast food dining during the COVID-19 pandemic, which is probably related to the decline in full-service restaurant dining and rising rates of food insecurity. We worry that the number of those with fatty livers has gone up even more since the time of the survey.”