This study is designed to determine if the amount of fat and saturated fat in the diet contributes to the development of a condition called fatty liver disease in the absence of changes in weight.

A condition called non-alcoholic steatohepatitis is characterized by fat accumulation in the liver and associated inflammation. This condition is strongly associated with obesity, insulin resistance and type 2 diabetes. Diets high in saturated fat result in fatty liver, insulin resistance and liver injury in animal models. Dietary composition may contribute not only to hepatic fat accumulation and insulin resistance but may also promote inflammation leading to chronic liver disease in humans. This study will test the hypothesis that a diet high in fat and saturated fat contributes to liver fat accumulation, insulin resistance and inflammation by comparing the effects of a four-week, weight stable high fat/high saturated fat diet (55% calories from fat/25% saturated fat) with a four-week, weight stable low fat/low saturated fat diet (20% fat/8% saturated fat) in overweight and obese subjects.

Inclusion Criteria:

• Age 18-55 years old, men and women, otherwise in good general health, BMI >27 kg/m2

Exclusion Criteria:

• Abnormal glucose tolerance, fasting glucose>100 mg/dl or diabetes
• History of liver condition or alanine aminotransferase (ALT) above the upper limit of the normal range
• Use of medications that cause insulin resistance or fatty liver: niacin, glucocorticoids, estrogens, tamoxifen, amiodarone, accutane, sertraline, atypical antipsychotics, anti-HIV medications
• Chronic use of anti-inflammatory medications (aspirin, ibuprofen, naprosyn, steroids, etc)
• Average alcohol intake >20 grams/day
• Tobacco use
• Creatinine >1.5 mg/dl for men and >1.4 mg/dl for women
• Hematocrit <33%
• Pregnancy or lactation
• Significant weight loss within the past 6 months (>5% body weight)
• Claustrophobia or any contraindications to being placed in the magnet for the MRS scan such as pacemakers, defibrillators, brain aneurysm clips, etc.
• Other serious medical conditions or inflammatory conditions such as cancer, inflammatory arthritis, etc.
• History of multiple food allergies or intolerances or severe food allergies
• History of coronary artery disease, history of or treatment of hyperlipidemia, LDL >200 mg/dl, fasting triglycerides >300 mg/dl
• Weight >300 pounds