Physical activity, exercise and non-alcoholic fatty liver disease

Abstract

Non-alcoholic fatty liver disease (NAFLD) represents a spectrum of liver conditions ranging from hepatic steatosis through steatohepatitis to cirrhosis. Its prevalence has been estimated at between one-in-five and one-in-three of the adult population depending on country and diagnostic criteria used. Prevalence increases with degree of obesity, and is very common in those with Type 2 diabetes (T2DM). Rising prevalence of obesity and T2DM, particularly in younger people, will ensure that NAFLD remains a growing clinical concern for the future. Lifestyle modification, which encompasses diet, weight loss, physical activity, and/or exercise related behaviours, is the primary recommended therapy for NAFLD, especially in the absence of approved pharmaceutical agents. Despite lifestyle modifications being central to the management of NAFLD, the evidence base upon which these guidelines are based is lacking, and this is particularly true for physical activity and exercise. The focus of this thesis is on defining, exploring and developing the evidence for physical activity and exercise in NAFLD with a view to improving clinical care. The work contained within this thesis demonstrates that low levels of physical activity are prominent in people with NAFLD and that targeting this with resistance exercise therapy confers benefits to both liver lipid and the factors promoting its accumulation. It also highlights alterations in cardiac structure and function in people with NAFLD in the absence of overt cardiac disease, which may provide a therapeutic avenue in which to decrease cardiac disease risk in people with fatty liver. Over the duration of the work described in this thesis, the number of studies reporting on exercise and liver fat in people with NAFLD has increased markedly. The new information contained within this thesis contributes to this body of knowledge and, over time, will improve the management of a condition that is an increasing burden to the people of the Western world.