Do your liver a favor and steer clear of fast food, new research urges.

People with obesity or diabetes who consumed 20% or more of their daily calories from fast food had severely elevated levels of fat in their liver compared to those who ate less fast food or none.

Even the general U.S. population had moderate increases in liver fat when fast food made up one-fifth or more of their diet, the study found.

“Healthy livers contain a small amount of fat, usually less than 5%, and even a moderate increase in fat can lead to nonalcoholic fatty liver disease,” said lead study author Dr. Ani Kardashian. She is a hepatologist with University of Southern California’s Keck School of Medicine, in Los Angeles.

“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,” Kardashian said in a university news release.

Kardashian said this is one of the first studies to demonstrate the negative impact of fast food on liver health.

Even a relatively modest amount can be harmful, she warned.

“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.”

For the study, the researchers used data from a nationwide health and nutrition survey conducted in 2017 and 2018 to determine the impact of fast-food consumption on fatty liver disease, also called liver steatosis. The condition can cause cirrhosis, or scarring, of the liver, and potentially lead to cancer or liver failure.

For this study, fast food and pizza from either a drive-through restaurant or one without wait staff were included.

The investigators compared fast-food consumption with fatty liver measurements in 4,000 adults.

About 52% consumed some fast food. Of those, 29% got at least one-fifth of their daily calories from fast food. About 29% had 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.”

More than 30% of the U.S. population has liver steatosis, the study authors noted.

Kardashian said she hopes the study will encourage health care providers to offer patients, especially those with obesity or diabetes, more nutrition education. The only way to treat liver steatosis is through better diet.

The findings were published online Jan. 10 in the journal Clinical Gastroenterology and Hepatology.

More information

The U.S. National Library of Medicine has more on fatty liver disease.

SOURCE: University of Southern California–Health Sciences, news release, Jan. 10, 2023