A study from Keck Medicine of USC published in Clinical Gastroenterology and Hepatology gives people additional motivation to reduce their fast food consumption.
The study found that eating fast food is associated with nonalcoholic fatty liver disease, a life-threatening condition in which fat accumulates in the liver.
Researchers found that people with obesity or diabetes who consume 20% or more of their daily calories from fast food have very high levels of liver fat compared to those who consume less or no fast food. And the general population has moderate increases in liver fat when one-fifth or more of their diet is fast food.
“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 Ani Kardashian, MD, hepatologist at Keck Medicine and author main of the study. “The severe increase in liver fat in people with obesity or diabetes is especially striking, and is likely due to the fact that these conditions cause increased susceptibility to fat accumulation in the liver.”
While previous research has shown a link between fast food and obesity and diabetes, this is one of the first studies to demonstrate the negative impact of fast food on liver health, according to Kardashian.
The findings also reveal that a relatively modest amount of fast food, rich in carbohydrates and fats , can damage the liver. “If people eat one meal a day at a fast food restaurant, they may think they’re doing no harm,” Kardashian said. "However, if that meal equals at least one-fifth of their daily calories, they are putting their livers at risk."
Nonalcoholic fatty liver disease, also known as hepatic steatosis , can lead to cirrhosis or scarring of the liver, which can lead to cancer or liver failure. Hepatic steatosis affects more than 30% of the US population.
Kardashian and her colleagues analyzed the most recent data from the nation’s largest annual nutritional survey, the 2017-2018 National Health and Nutrition Examination Survey, to determine the impact of fast food consumption on fatty liver.
The study characterized fast food as meals, including pizza, from a self-service restaurant or one without waiters.
The researchers evaluated the fatty liver measurements of approximately 4,000 adults whose fatty liver measurements were included in the survey and compared these measurements to their fast food consumption.
Of those surveyed, 52% ate some fast food. Of these, 29% consumed a fifth or more of their daily calories from fast food. Only this 29% of survey subjects experienced an increase in liver fat levels.
The association between hepatic steatosis and a 20% fast food diet remained stable for both the general population and people with obesity or diabetes, even after the data were adjusted for many other factors, such as age, sex, race, ethnicity, alcohol consumption, and physical activity.
“Our findings are particularly alarming since fast food consumption has increased over the past 50 years, regardless of socioeconomic status,” Kardashian said.
“We have also seen a substantial increase in fast food during the COVID-19 pandemic, which is likely related to the decline in full-service restaurant dining and increased rates of food insecurity. “We are concerned that the number of people with fatty liver has increased further since the time of the survey.”
She hopes the study will encourage health care providers to offer patients more nutrition education, especially those with obesity or diabetes who are at higher risk of developing fatty liver from fast food. Currently, the only way to treat fatty liver disease is through an improved diet.
Jennifer Dodge, MPH, assistant professor of research medicine and population sciences and public health at the Keck School of Medicine of USC and Norah Trault, MD, MPH, gastroenterologist at Keck Medicine and division chief of gastroenterology and liver diseases at the Keck School, were also authors of the study.
