Study Title:

Aerobic Exercise Improves Fatty Liver

Study Abstract

Weight loss remains the most common therapy advocated for reducing hepatic lipid in obesity and nonalcoholic fatty liver disease. Yet, reduction of body weight by lifestyle intervention is often modest, and thus, therapies which effectively modulate the burden of fatty liver but are not contingent upon weight loss are of the highest practical significance. However, the effect of aerobic exercise on liver fat independent of weight loss has not been clarified. We assessed the effect of aerobic exercise training on hepatic, blood, abdominal and muscle lipids in 19 sedentary obese men and women using magnetic resonance imaging and proton magnetic resonance spectroscopy (1H-MRS). Four weeks of aerobic cycling exercise, in accordance with current physical activity guidelines, significantly reduced visceral adipose tissue volume by 12% (P < 0.01) and hepatic triglyceride concentration by 21% (P < 0.05). This was associated with a significant (14%) reduction in plasma free fatty acids (P < 0.05). Exercise training did not alter body weight, vastus lateralis intramyocellular triglyceride concentration, abdominal subcutaneous adipose tissue volume, 1H-MRS-measured hepatic lipid saturation, or HOMA-IR (homeostasis model assessment of insulin resistance; P > 0.05). Conclusion: 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. Physical activity should be strongly promoted for the management of fatty liver, the benefits of which are not exclusively contingent upon weight loss.

From press release:

Researchers from the University of Sydney, Australia determined that patients with a sedentary lifestyle who engage in routine physical activities lower their risk of nonalcoholic fatty liver disease (NAFLD). The lower risk of problems associated with fatty liver was not contingent upon weight loss, but a direct result from the increased aerobic exercise.

The results of this study are published in the October issue of Hepatology, a journal of the American Association for the Study of Liver Diseases.

Nonalcoholic fatty liver disease affects 30% of the adult population and the majority of obese individuals. The condition, where fat accumulates in the liver of those people who drink little or no alcohol, can cause inflammation or scarring of the liver with more serious cases, known as nonalcoholic steatohepatitis, possibly progressing to liver failure.

A study, led by Jacob George, M.D. from Westmead Hospital at the University of Sydney, included 19 obese adults who had a body mass index >30 kg/m2 and reported a sedentary lifestyle. Baseline measurements were performed to determine hepatic triglyceride concentration (HTGC) and hepatic lipid saturation index (SI), intramyocellular triglyceride (IMTG) levels, visceral adipose tissue (VAT) or amount of fat stores in the abdomen, cardiorespiratory fitness, blood biochemistry, and measurements for body height and weight. Volunteers either received 4 weeks of aerobic cycling exercise (12 subjects) or a placebo (7 participants), which involved regular stretching.

At the end of the 4-week period, measurements were again taken from each participant. Body weight and body mass index (BMI) remained unchanged, but cardiorespiratory fitness significantly improved in the exercise group versus placebo. Researchers noted a 21% reduction of HTGC and 12% VAT volume in those participants who were subject to regular exercise. "Our data provides the first direct experimental evidence that regular aerobic exercise reduces fatty liver in obesity without concurrent changes in body weight or abdominal fat," explained researchers.

Individuals who are obese are at risk for a number of cardiovascular and metabolic health concerns, including heart disease and diabetes. "Our observation of the beneficial effect of regular exercise itself on liver and abdominal fat should refocus the debate on the role of physical activity in the prevention and management of obesity and NAFLD," concluded Dr. George. Past studies have shown that exercise adherence appears to be more sustainable over time than weight loss. "Further studies of the long-term benefit of routine physical activity on lowering HTGC and its impact on obesity and NAFLD should be explored," recommended Dr. George.

Study Information

A. Johnson, Toos Sachinwalla, David W. Walton, Kate Smith, Ashley Armstrong, Martin W. Thompson, Jacob George.
Aerobic exercise training reduces hepatic and visceral lipids in obese individuals without weight loss.
Hepatology
2009 October
Institute of Obesity, Nutrition and Exercise, The University of Sydney, Australia.

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