People with fatty livers need to lose weight

By Sally Robertson, B.Sc.May 31 2012

Exercising moderately for 150 to 300 minutes a week does not improve lipoprotein metabolism in obese people with nonalcoholic fatty lipid disease (NAFLD), show findings from a US study.

The marked improvement in fatty liver and lipoprotein metabolism that is associated with lifestyle intervention may be largely due to weight loss rather than increased physical activity, suggest Samuel Klein (Washington University School of Medicine, St Louis, Missouri) and colleagues.

Diet-induced weight loss and regular physical activity has previously been shown to reduce intrahepatic triglyceride (IHTG) content and improve the metabolic derangements associated with NAFLD, explain the researchers. "However, few studies have evaluated the effect of regular physical activity, independent of weight loss, on NAFLD," they say.

Current physical activity guidelines from the Department of Health and Human Services recommend that adults perform at least 150 minutes, but preferably 300 minutes, of moderate-intensity physical activity per week, note Klein et al.

The team decided to investigate the effect of following these guidelines on IHTG and very low-density lipoprotein (VLDL) kinetics in 18 obese patients with NAFLD.

The researchers randomly assigned 18 obese individuals (mean body mass index [BMI] 38.1 kg/m²) with NAFLD (IHTG content >10%) to either participate in an exercise regimen (exercise group) or to continue their current daily activities (control group) over a 16-week period. Those in the exercise group were instructed to exercise for 30-60 minutes, five times per week, at 45-55% of their peak oxygen consumption (ie, a brisk walk).

The team used magnetic resonance spectroscopy to assess IHTG content and isotopically labeled tracer techniques to examine VLDL-TG and VLDL-apolipoprotein B-100 (apoB-100) kinetics among the participants at baseline and at 16 weeks.

As reported in Hepatology, there were no differences in body weight, body fat mass, and fat-free mass values among the participants at 16 weeks, compared with baseline.

The researchers found that there was a 10.3% relative decrease in IHTG content in the exercise group, compared with the control group.

Interestingly, the exercise training did not affect plasma total TG, VLDL-TG, VLDL-apoB-100, or fasting fatty acid concentrations.

However, there was a 12.8% relative decrease in plasma alanine transaminase (ALT) concentration, compared with in the control group, and this decrease correlated directly with the change in IHTG content.

"These results demonstrate that moderate-intensity endurance exercise training alone has only modest therapeutic effects on hepatic TG and lipoprotein metabolism," say Klein et al.

The improvement in lipoprotein metabolism and steatosis observed with lifestyle intervention may be due to weight loss and not increased physical activity, they say.

"Further studies are needed to evaluate the mechanism through which moderate-intensity exercise training decreases IHTG content," concludes the team.

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