Feb. 13, 2023 -- Exercise training can lead to a significant reduction in liver fat for patients with nonalcoholic fatty liver disease, a leading cause of liver disease worldwide, according to a new study published in the American Journal of Gastroenterology.
People in the study needed about 150 minutes per week of moderate-intensity exercise, such as brisk walking, or 75 minutes per week of vigorous-intensity exercise, such as jogging or cycling.
“Exercise remains a key component in the clinical management of NAFLD for all patients with this common condition and should be discussed at each and every health care visit,” says study co-author Jonathan Stine, MD, associate professor of medicine and public health sciences and director of the Fatty Liver Program at the Pennsylvania State University-Milton S. Hershey Medical Center.
“We need to do more as a medical society in helping to support our patients with NAFLD in making healthy lifestyle choices by providing a supportive environment that is rich with exercise-based information and resources,” he says.
NAFLD affects nearly 30% of people worldwide. Over time, it can lead to cirrhosis and cancer. Exercise training has shown multiple benefits for patients with NAFLD, including improvements in liver fat, physical fitness, body composition, vascular biology, and health-related quality of life.
But it's been unclear whether exercise training achieves a 30% relative reduction in liver fat, which is considered the threshold to see a clinical difference and NAFLD improvement.
Stine and colleagues analyzed the evidence for MRI-measured liver reduction in response to exercise training, including whether a 30% or more relative reduction could be achieved across different amounts of exercise. They included randomized, controlled trials in adults with NAFLD who participated in exercise training programs.
Among 14 studies with 551 participants, the average age was 53, and the average body mass index was 31. The studies ranged from 4 to 52 weeks and included different types of exercise training, such as aerobic, high-intensity interval training, resistance training, and aerobic plus resistance training. The average weight loss was about 2.8% among those who participated in exercise training.
In general, those who participated in exercise training were more likely to achieve a 30% or more relative reduction in MRI-measured liver fat. Specifically, they were 3.5 times more likely to achieve the target than those in the control group.
Among the 551 people, the average change in absolute liver fat was -6.7% for the 338 people enrolled in exercise training, as compared with -0.8% for the 213 people in the control group. In nine studies with 195 people, the average change in relative liver fat was -24.1% among the exercise training group and +7.3% among the control group.
For all 14 studies, an exercise dose of 750 or more metabolic equivalent of task minutes (MET-min) per week resulted in a significant response. This equals 150 minutes per week of moderate-intensity exercise, such as brisk walking, or 75 minutes per week of vigorous-intensity exercise, such as jogging or cycling.
An exercise dose of 750 or more MET-min per week led to a 30% or more relative reduction in MRI-measured liver fat in 39.3% of people, as compared with 25.7% who had fewer than 750 MET-min per week. The reduction happened regardless of weight loss.
“Our work highlights a novel way to approach this important topic,” Stine says. “The goal of exercise training in patients with NAFLD should no longer be to lose body weight, but rather, to improve their NAFLD, physical fitness, and overall health.”
At this time, there is no consensus from leading professional societies regarding the optimal physical activity program for patients with NAFLD, the study authors write. That said, most current clinical guidelines support at least 150 minutes per week of moderate-intensity aerobic activity.
“Exercise gives us many benefits that we do not see. The number on the scale should not be the only thing that we are looking at,” says Jill Kanaley, PhD, a professor of nutrition and exercise physiology at University of Missouri.
Kanaley, who wasn't involved with this study, has researched exercise training among patients with NAFLD. She and colleagues have found that moderate-intensity and high-intensity exercise can decrease NAFLD risk factors even if there aren't reductions in belly fat or weight.
“Exercise benefits many systems without weight loss, prevents weight gain, and helps mental health,” she says. “Just getting up and moving makes you feel better.”