This project examines the effects of a 4 month structured exercise intervention program in patients with non-alcoholic fatty liver disease (NAFLD). We will examine changes in total and depot-specific (i.e.in different tissues, liver, muscle and pancreas)fat. We will correlate these with measurements of the insulin from the liver. The hypothesis is that by reducing fat in these specific depots we can reduce insulin resistance and prevent progression to diabetes.

1. Exercise program: We are asking people to take part in a supervised exercise program for 4 months. This involves on average a weekly supervised exercise bout plus other unsupervised exercise bouts at home. We will ensure participants are physically able to embark on this by taking their medical history, physical examination and validated questionnaire (PARQ). This program is for the benefit on the patients' long term health.

2. MR imaging to assess fat: occassionally these may pick up anomalies which require further investigation. A radiologist will screen the abdominal images and GP will be informed on anything requiring further investigation.

   No radiation is received during MR imaging.

3. Physiological studies: Patients will be asked to attend for 2 non-consecutive days before and after the exercise intervention. Regular blood samples will be required as apart of these investigations.

Inclusion Criteria:

• Sedentary, non smoking, male subjects,
• Alcohol consumption men <21 units/week,
• BMI 27-35. (Lean individuals do not suffer from NAFLD, so are not suitable for this study. Conversely, we are restricted to a maximum BMI of 35 due to the size limitations of the MR scanner.)
• A clinical diagnosis of NAFLD based upon the following criteria: i) exclusion of other causes of liver disease i.e. negative Hepatitis B and C serology, a negative auto-immune profile and normal caeruloplasmin concentrations, ii) Ultrasound appearances suggestive of a fatty, echo-bright liver with no evidence of cirrhosis (in some cases, the diagnosis will have been confirmed histologically after liver biopsy.
• Being willing to engage and motivated to follow an exercise program.

Exclusion Criteria:

• Prescription of corticosteroids, amiodarone, tamoxifen, methotrexate (drugs known to cause secondary steatohepatitis) or fibrates. Statin is Ok as long as the patients are on stable therapy for a while, if changed then the patient will be excluded.
• Alcohol consumption for men 21 units/week.
• A contraindication to exercise (such as unstable ischaemic heart disease),
• Type 2 diabetes (type 2 diabetes patients are excluded so that we are examining the involvement of insulin resistance at a reversible stage before β-cell failure has occurred).
• Patients who are on medications that will interact with GTN (glyceryl trinitrate) will be excluded from the GTN dilatation (endothelial independent NO mediated function) aspect of the study.
• Individuals who suffer from claustrophobia and have metal implants will be excluded from the MRI aspect of the study.
• Patients who smoke will also be excluded from the study.
• Total cholesterol >7