Fitness versus fatness: Moving beyond weight loss in nonalcoholic fatty liver disease

Abstract

The rapid emergence of nonalcoholic fatty liver disease (NAFLD) as a cause of both liverrelated morbidity and mortality and cardiometabolic risk has led to the search for effective lifestyle strategies to reduce liver fat. Lifestyle intervention comprising dietary restriction in conjunction with increased physical activity has shown clear hepatic benefits when weight loss approximating 3%-10% of body weight is achieved. Yet, the poor sustainability of weight loss challenges the current therapeutic focus on body weight and highlights the need for alternative strategies for NAFLD management. Epidemiologic data show an independent relationship between liver fat, physical activity, and fitness, and a growing body of longitudinal research demonstrates that increased physical activity participation per se significantly reduces hepatic steatosis and serum aminotransferases in individuals with NAFLD, independent of weight loss. Mechanistic insights to explain this interaction are outlined, and recommendations for the implementation of lifestyle intervention involving physical activity are discussed. In light of the often poor sustainability of weight loss strategies, and the viability of physical activity therapy, clinicians should assess physical fitness and physical activity habits, educate patients on the benefits of fitness outside of weight loss, and focus on behavior change which promotes physical activity adoption. (HEPATOLOGY 2010;52:370-381)

Non‐alcoholic fatty liver disease (NAFLD) is associated with low level of physical activity: a population‐based study

“…Most published data suggest that this is the case, but these data have been derived from self-reports. 26,27 Self-reports are reliable, but the sensitivity of the data with respect to amount of time spent and level of intensity of the activity has been difficult to validate. 28 We chose to use the NHANES survey (2003-2004 and 2005-2006) because it reported data collected from an activity monitor.…”

Physical activity, sedentary time, and liver enzymes in adolescents: the HELENA study

“…Regular PA is known to be associated with lower total and central adiposity (17,18,26) as well as with lower insulin resistance (23,27) in children and adolescents. Therefore, it is biologically plausible that regular PA preserves the hazard effects of adiposity and insulin resistance on liver function enzymes (24,25). The increased hepatic lipogenesis and triglyceride-rich lipoprotein secretion induced by excess of central adiposity (2) might also be attenuated by regular PA, as several studies have unequivocally shown that PA is associated with a healthier blood lipid profile (21,22).…”

“…Intervention studies investigating the effectiveness of regular PA on NAFLD in obese children and adolescents (29)(30)(31)(32) support weight loss in reversing the progression of NAFLD. Recent evidence also suggests that exercise may play a key role on hepatic fat content by directly altering hepatic β-oxidation and/or lipogenesis (25).…”

“…Moreover, there is no doubt regarding the detrimental consequences for health of a prolonged sedentary lifestyle. Studies examining the association of objectively measured physical activity (PA) and sedentary time with liver enzymes in youth are scarce (6), yet it is biologically plausible that both lifestyle factors are associated with fatty liver enzyme levels at this age (24,25). We hypothesized that MVPA and sedentary time are associated with AST, ALT, AST/ALT, and GGT in adolescents.…”

Exercise for NAFLD: Does Intensity Matter?

“…Studies have shown that dietary intervention needs to be intense, with frequent clinic visits to show a signifi cant improvement in liver histology in patients with biopsy-proven NASH. Physical activity can help maintain the weight loss and also improve IR, and recent data suggest that patients who show histological improvement tend to be more active ( 4 ). However, it has been diffi cult to differentiate the individual eff ects of physical activity and weight loss on the overall histological response in published studies.…”