Study in The Journal of Physiology found that mice bred to have a lower aerobic capacity had disease symptoms.

Researchers from the University of Missouri report finding biochemical links between low aerobic fitness and fatty liver disease. Their findings suggest that the resulting liver problems play a crucial step toward developing obesity-related illnesses.

Poor aerobic fitness is strongly associated with other metabolic disorders like obesity and its consequent risks of heart disease, stroke, and diabetes. The Missouri team wanted to test the mechanism behind the link between fitness and fatty liver disease.

Described in the The Journal of Physiology, they selectively bred two groups of rats with different levels of intrinsic aerobic capacity. After 17 generations of careful breeding, the unfit rats could run an average of 200 m compared to over 1,500 m achieved by the fit rats.

The study called “Rats selectively bred for low aerobic capacity have reduced hepatic mitochondrial oxidative capacity and susceptibility to hepatic steatosis and injury,” found the effect on the rats’ livers was devastating. At 25 weeks old, the unfit group was displaying clear symptoms of nonalcoholic fatty liver disease-weakened mitochondria, poor fat processing power, high fat retention, and other abnormalities. By the end of their natural lives, the rats’ livers had sustained damage including fibrosis and unexpected cell death. In contrast the fit group had healthy livers throughout their lifespan despite the fact that neither group was getting any real exercise.

“Fatty liver disease will be the next big metabolic disorder associated with obesity and inactivity,” according to John Thyfault of the University of Missouri, lead author of the study. “It also is a significant contributor to type 2 diabetes.”

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