The study is designed to determine the effect of high physical activity level vs. low physical activity level on the adaptation to a high fat diet.

A high fat diet is linked to weight gain and obesity. An adjustment to the acute exposure to high fat diet is not abrupt and takes time. In a previous study from our laboratory, it has been shown that high level of physical activity can accelerate the adaptation to a high fat diet by increasing fat oxidation. In this study we will determine the mechanism involved in this adjustment. Our hypotheses are:

1. High fat diets decrease skeletal muscle glucose metabolism and decrease mitochondrial biogenesis through the upregulation of PDK4 and downregulation of PGC1α; increased physical activity will prevent these deleterious effects.
2. A high fat diet will increase hepatic and skeletal muscle lipid; increased physical activity will prevent these deleterious effects.
3. These effects are more pronounced in individuals with a low mitochondrial content

Inclusion Criteria:

• Both genders and all races will be invited to participate
• BMI > 19 and < 35 kg/m2
• Age 18-35
• Women will be asked to participate in the follicular phase of the menstrual cycle as determined by menstrual history and a negative pregnancy test will be recorded prior to participation
• Willing and able to walk on a treadmill at a pace of 3 mph at 3%grade for 3-4 hours/day for 3 consecutive days
• Willing to eat only and all foods provided by Pennington for 9 days on 2 occasions (18 days)
• Willing to stop alcohol consumption for the duration of the study
• Able come to Pennington for meals and tests for 20 days 12 of these inpatient.

Exclusion Criteria:

• Significant renal, hepatic, endocrine, pulmonary, cardiac or hematological disease (for the consent form you will have to use kidney, liver, etc )
• You abuse alcohol or illegal drugs or are unable to avoid alcohol or caffeine prior to testing
• Smokers
• Unable or unlikely to eat all and only food provided by the PBRC metabolic kitchen.
• Pregnant or planning to become pregnant
• Corticosteroid use in previous two months
• Chronic use of anti-diabetic, anti-hypertensive, or other medications known to affect fat metabolism
• Use of Depo-Provera, hormone implants or estrogen replacement therapy
• Irregular menstrual cycles
• Post-menopausal women
• Weight gain or loss of > 3kg in the last 6 months
• Unable or unwilling to perform treadmill walking at the required speed and incline to achieve 1.8*RMR
• History or family history of blood clots deep vein thrombosis or pulmonary embolism)
• Poor circulation, bypass operation on legs, blood coagulation disorders, diagnosed peripheral arterial or vascular disease, cramping pain in your muscle during exercise or nerve damage in your legs.
• You had major surgery on the abdomen, pelvis or legs within previous 3 months.
• You have cancer
• You have rheumatoid disease/ walking or joint problems
• You are claustrophobic
• You are depressed or have an eating disorder
• You demonstrate a style of interpersonal relationships that would inhibit successful completion of the study

For the MRS / MRI, the following exclusion criteria apply:

• Individuals who have a heart pacemaker, defibrillator, or non-removable hearing aid
• Individuals with any clips or metal plates in their head
• Individuals who have any artificial limbs or prosthetic devices
• Individuals who were ever injured by a metallic foreign body which was not removed
• Individuals with bridgework held in place by magnets