Study leader Dr. Nathan Johnson, of the University of Sydney in Australia, and his team publish their findings in the Journal of Hepatology.
Nonalcoholic fatty liver disease (NAFLD) – an accumulation of fat in liver cells that is not caused by alcohol – is estimated to affect around 25% of people in the US. It most commonly occurs among overweight or obese individuals and those who have diabetes, high cholestrol or high triglycerides.
While the condition causes no symptoms or complications for the majority of people, others may experience liver inflammation, known as nonalcoholic steatohepatitis (NASH). This may lead to liver scarring (cirrhosis) and, eventually, liver cancer or liver failure.
At present, there is no standard treatment for NAFLD. For people with NAFLD who are overweight or obese, health care professionals recommend losing weight. Past studies have suggested that doing so through aerobic exercise can reduce the amount of abdominal (visceral) fat and fat in the liver, improving symptoms.
But according to Dr. Johnson and colleagues, it is unclear what volume and intensity of aerobic exercise are required to pose such benefits for patients with NAFLD. They aimed to find out with their study.
All exercise volumes, intensities led to reduction in liver and visceral fat
The team enrolled 48 overweight or obese individuals with sedentary lifestyles, meaning they rarely engaged in physical activity.
The participants were randomly assigned to one of four exercise groups for 8 weeks: a low-to-moderate intensity, high-volume aerobic exercise (LO:HI) group, a high-intensity, low-volume aerobic exercise (HI:LO) group, a low-to-moderate intensity, low-volume aerobic exercise (LO:LO); and a placebo group.
During the 8-week period, Dr. Johnson and his team used magnetic resonance spectroscopy (MRS) to measure any changes in participants’ liver fat.
The researchers found that participants in the placebo group saw their liver fat increase by around 14%. Participants in the three exercise groups, however, had an average 18-29% reduction in liver fat during the 8-week period, with the greatest liver and visceral fat reduction found in participants in the HI:LO and LO:HI groups.
Commenting on their findings, Dr. Johnson says:
“The results from our study show that all exercise doses, irrespective of volume or intensity, were efficacious in reducing liver fat and visceral fat by an amount that was clinically significant, in previously inactive, overweight or obese adults compared with placebo. These changes were observed without clinically significant weight loss.”
In an editorial linked to the study, Dr. Roohit Loomba, of the University of California-San Diego, and Dr. Helena Cortez-Pinto, of the Hospital de Santa Maria in Lisbon, Portugal, say that although there is evidence to support that aerobic exercise – even in the absence of weight loss – may reduce liver fat in patients with NAFLD, “there is no data to support that exercise alone without weight loss can improve or reverse NASH.”
“The individual and joint effect of dose and intensity of exercise and their association with improvement in liver fat and other histologic features that are associated with NASH is a key research priority,” they add.
“In our expert opinion, a more stringent exercise regimen than the US Department of Health and Human Services recommends, coupled with dietary interventions, may be needed to induce improvement in liver histologic features associated with NASH.”