Evidence is accumulating that there are sex differences in energy and substrate metabolism. The positive or negative consequences of such metabolic differences between men and women need to be evaluated with respect to health outcomes. The importance of aberrant lipid metabolism in metabolic diseases such as obesity, diabetes and cardiovascular disease, makes understanding the distinction between "normal" vs aberrant critical to future treatment and prevention strategies. Sex differences in the effects of catecholamines on lipid metabolism and substrate oxidation in non-obese, healthy individuals, have been consistently observed. In addition, distinct differences in men and women exist in the distribution of body fat, with men typically having greater central adiposity than women. Accumulation of fat in the abdomen is associated with an increased risk for metabolic abnormalities such as hyperlipidemia and insulin resistance. In the current study, therefore, the role of testosterone in determining the sex differences in catecholamine mediated substrate metabolism and deposition of dietary fat into upper versus lower body adipose tissue depots will be addressed.

Inclusion Criteria:

• normal weight (BMI of 23-29.9 kg/m2)
• not be highly trained (< 5hrs of moderate intensity, planned exercise per week).

Exclusion Criteria:

• Patients will be excluded if they have one or more of the following out-of-range values measured on a fasting blood sample:

• glucose <65 or > 110 mg/dl,

• insulin > 20 uU/ml,

• thyroid stimulating hormone <0.5 or >5.0 uU/ml,

• growth hormone >2.5 ng/ml.

• Subjects who may be:

• anemic (hemoglobin < 14.5 g/dl men ),

• have abnormal liver function tests:

  • alanine amino transferase > 47 U/l,
  • aspartate aminotransferase, > 47 U/l,
  • alkaline phosphatase <39 or >117 U/l) or
  • creatinine (<0.6 or >1.1 mg/dl).