Associations between dietary intake, physical activity and intrahepatic fat.
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Excess accumulation of intrahepatic fat (IHF) is directly involved in the pathogenesis of insulin resistance and dyslipidemia, which are risk factors for type 2 diabetes and cardiovascular disease. To our knowledge, no prior groups have examined the inter-relationship between diet quantity, macronutrient composition, physical activity (PA), and IHF. The objective of the enclosed thesis is to investigate the associations of simultaneously measured objective PA and dietary intake in relation to IHF. The Liver Fat Study was conducted on middle-aged, abdominally obese, inactive men (n=4) and women (n=20) between the ages of 40 and 70 years old. Participants were instructed to record their food intake and wear an accelerometer for objective measurement of PA for 7 days. Thereafter, insulin resistance was assessed by HOMA-IR using fasting insulin and glucose, cardiorespiratory fitness (CRF) was measured by a graded exercise treadmill test, abdominal adiposity was measured by magnetic resonance imaging (MRI), anthropometrics were measured by waist circumference (WC) and BMI, and IHF was measured by proton-magnetic resonance spectroscopy (H-MRS). While none of the dietary intake (quantity or macronutrient composition) or PA variables were significantly associated with IHF (p>0.05), CRF, WC, visceral adipose tissue (AT), and HOMA-IR were associated with IHF (p<0.05). Additionally, sedentary time, light PA and total PA approached statistical significance with visceral AT, while both light PA and total PA were significantly associated with WC (p<0.05). The findings from this study suggest that all components of PA, while not directly associated with IHF, are indirectly associated with IHF through its influence on abdominal obesity. This finding emphasizes the importance of PA, separate from the national guidelines, as a treatment target for clinicians.