The purpose of this pilot study is to determine whether adipose tissue loses some of its ability to expand in response to overfeeding in older compared to younger men. The investigators hypothesize that the adipose tissue response to overfeeding may be weakened in older when compared to younger men, thereby leading to worsened ectopic storage depots for older men.

This pilot study will begin to address whether adipose tissue biology changes with advancing age. Specifically, we will test whether adipose tissue loses some of its ability to expand in response to overfeeding in older compared to younger men. To test this possibility the Investigators will recruit overweight and mildly obese older (age 55-75y) and younger (age 25-40y) men and collect adipose tissue biopsies before and after 7 days of overfeeding. The investigators will test how well the cells in adipose tissue expand in response to overfeeding and whether this differs between younger and older men.

Inclusion Criteria:

• Men
• Aged 25-40y OR 55-75y
• BMI 28-35 kg/m2
• Weight stable (±2kg over past 3 mo)
• Sedentary to moderately active (<3 d/wk of exercise lasting >20min)
• Non-smokers (never used or quit >7yrs prior)

Exclusion Criteria:

• Women
• Currently using hormones, glucose or lipid lowering medication
• Engaged in exercise or diet program
• Currently gaining or losing weight or using weight loss drugs
• Diabetes mellitus (diagnosis, treatment, FBG ≥126 mg/dL)
• Uncontrolled metabolic disorders (e.g., thyroid)