From Medscape Medical News
Deborah Brauser
September 11, 2009 — Obese individuals with a sedentary lifestyle can lower their risk for nonalcoholic fatty liver disease (NAFLD) by engaging in routine physical activities, according to results of a small randomized study published online June 15 in Hepatology.
In addition, this lower risk was not contingent upon weight loss, but was a direct result of the increased exercise program.
"These data provide the first direct experimental evidence demonstrating that regular aerobic exercise reduces hepatic lipids in obesity even in the absence of body-weight reduction," write Nathan A. Johnson, from the Discipline of Exercise and Sport Science and the Institute of Obesity, Nutrition and Exercise at the University of Sydney in Australia, and colleagues.
"Physical activity should be strongly promoted for the management of fatty liver," add the study authors.
The location of body fatness, particularly visceral adipose tissue (VAT), is increasingly recognized as being of greater importance in determining the metabolic and cardiovascular consequences of excess adiposity, the authors report.
In addition, evidence is emerging that excessive storage of hepatocellular triglyceride is a common feature of obesity, with hepatic steatosis (or NAFLD) possibly affecting 30% of the adult population and the majority of obese individuals.
However, there is a paucity of evidence regarding the effects of diet and exercise interventions on reducing hepatic triglyceride concentration (HTGC), and no definitive pharmacotherapy exists for it.
Strategies Besides Those Aimed at Weight Loss Are Needed
"Although intervention aimed at weight loss is advocated, reductions in weight by dietary restriction are typically modest and are increasingly viewed as an unsustainable outcome of lifestyle modification," write the study authors. "Therefore, appropriate therapeutic strategies for reducing HTGC, which are not contingent upon weight loss, are needed."
Although the effect of aerobic exercise on liver fat independent of weight loss has not been clarified, the investigators sought to assess its effect on hepatic, blood, abdominal, and muscle lipids for this study.
Dr. Johnson and his team enrolled 23 obese adults who had a body mass index of 30 kg/m2 or higher and who reported a sedentary lifestyle and low alcohol intake (0-20 g/day).
Baseline measurements were performed to determine HTGC and saturation index, abdominal VAT and subcutaneous adipose tissue (SAT) area and volume, intramyocellular triglyceride concentration, cardiorespiratory fitness, anthropometry, and blood biochemistry.
A total of 19 patients were then randomly allocated to receive either 4 weeks of supervised aerobic exercise training (n = 12) made up of 3 cycle ergometer sessions (30–45 minutes each) per week or 4 weeks of a sham intervention (placebo, n = 7). Those in the placebo group received 1 supervised stretching session at treatment initiation and were then directed to perform the stretches 3 times per week at home.
The investigators measured HTGC with noninvasive proton magnetic resonance spectroscopy and measured abdominal lipids by magnetic resonance imaging. Cardiorespiratory fitness was assessed using the Physical Work Capacity test undertaken on a cycle ergometer. All measurements for both groups were repeated at completion of the allocated exercise programs.
After 4 weeks of aerobic cycling exercise, VAT volume was significantly reduced by 12% (P < .01) and HTGC was reduced by 21% (P < .05).
The aerobic exercise regime was also associated with a significant (14%) reduction in plasma free fatty acids (P < .05).
Exercise training did not alter body weight, vastus lateralis intramyocellular triglyceride, abdominal SAT volume, magnetic resonance spectroscopy-measured hepatic lipid saturation, or homeostasis model assessment of insulin resistance (P > .05).
First Direct Evidence
"Using a short-term aerobic cycling training intervention in previously sedentary obese adults, we provide the first direct experimental evidence demonstrating that regular aerobic exercise training reduces hepatic lipids without concurrent changes in body weight or abdominal SAT content," write the study authors. "Thus, regular exercise may mitigate the metabolic and cardiovascular consequences of obesity, including fatty liver."
"Our observation of a beneficial effect of regular exercise itself . . . should refocus the debate, and hence policy, on the role of physical activity in the prevention and management of obesity and NAFLD. In other words, physical activity should be strongly promoted for the management of fatty liver," conclude the study authors.
Hepatology. 2009;50:000-000. Abstract
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