Exercise can benefit more than just the heart and muscles. New research from University of Missouri researchers suggests it may also improve liver health — but the way the body responds could differ between men and women.
Researchers found that endurance exercise changed how liver cells produced energy in male and female rats. Both groups showed improvements in liver health, but they appeared to reach those results through different biological pathways.
Scott Rector, an MU School of Medicine professor of nutrition & exercise physiology, said researchers have known for years that exercise benefits the heart and muscles, but its effects on the liver have received less attention.
“We typically think about exercise or endurance exercise or aerobic exercise training as something that impacts the heart and maybe your muscle,” Rector said. “But we've known for the last 15 or 20 years that exercise can have a pretty powerful impact on the liver as well.”
The study was part of a larger National Institutes of Health-funded effort to understand how exercise affects different organs in the body. Researchers examined changes in liver genes and proteins after eight weeks of aerobic exercise training.
Researchers studied both male and female animals and found that exercise improved liver health in both groups.
The findings included less fat in the liver, better cholesterol processing and lower levels of markers associated with fibrosis — a buildup of scar tissue that can develop as liver disease progresses.
But Rector's team also found differences in how male and female liver cells adapted to exercise.
Female rats produced more proteins in the mitochondria, the structures inside cells that generate energy. Male rats, meanwhile, showed more chemical changes to proteins already present in their mitochondria.
Rector compared the differences to how a factory operates.
“In the females, we increased the machinery in the mitochondria. So we made more proteins in order to, in theory, make the mitochondria function better,” he said. “Whereas the males didn't necessarily increase the amount of mitochondria. They increased the chemical modifications of the proteins that are in the mitochondria that could impact and improve the function of the mitochondria.”
Researchers don't yet know exactly why the two groups responded differently. They also did not directly measure whether the changes improved mitochondrial function.
But Rector said the differences do not mean one group benefited more than the other.
“I don't think that it benefited one sex over the other,” he said. “Both of them had beneficial health outcomes when we look at the mitochondria. There's lower fats and different types of fats in both of the sexes. We also saw that there are improvements in the markers of fibrosis in both of the sexes.”
The research could eventually inform treatments for metabolic dysfunction-associated steatotic liver disease, or MASLD. The condition, previously known as fatty liver disease, occurs when excess fat builds up in the liver. More than 100 million Americans have the condition. It is also closely linked to other health problems, including Type 2 diabetes, obesity and cardiovascular disease.
Exercise is already known to improve liver health in people with the condition. Rector said studies have found that physical activity can reduce liver fat even without weight loss. Exercise combined with weight loss can also reduce inflammation and scarring.
Rector said future research could examine whether exercise produces similar results in animals with liver disease or those eating a diet higher in fat and refined sugars.
For now, he said, the findings do not change exercise recommendations for men and women. Both should aim to increase their physical activity.
Rector said exercise does not have to mean going to a gym or doing strenuous workouts. Even shorter walks throughout the day can help people become more active.
“Hopefully in the future we might be able to tailor exercise in a different way that could benefit men versus women,” he said. “But right now as it stands, we should be promoting increasing physical activity.”
He recommends aiming for 30-45 minutes of moderate physical activity most days of the week, while increasing activity at a level people can manage.
