Adults who gain most of their excess weight in the abdominal area typically do not respond to things that "turn off" fat cells the same way as lean people. The researchers are trying to understand why fat tissue responds differently in people with different body types.

Inclusion Criteria:

• Males and females between 18 and 65 years of age who are able to comprehend instructions, follow study procedures, willing to sign an informed consent form, and consume an isoenergetic diet eating all meals from Mayo CRTU for at least 3 days prior to study.
• Overweight/Obese volunteers will have a BMI 29.0 - 40.0 kg/m2.
• Upper body/visceral obesity (UBO) in women will be defined as those with a waist-hip ratio (WHR) > 0.85 and/or increased visceral fat by single slice CT scan, usually with > 120 cm2 of visceral fat by CT scanning or a visceral fat/total fat ratio of > 0.30, and/or biochemical evidence of metabolic syndrome as defined by ATP III criteria (fasting plasma triglycerides ≥ 150 mg/dL, HDL-cholesterol < 50 mg/dL for women and < 40 mg/dL for men, fasting plasma glucose ≥ 100 mg/dL). Upper body obesity in men will be defined as a waist-hip ratio of > 0.95 and/or increased visceral fat (visceral fat area > 180 cm2 or a visceral/total fat abdominal ratio by CT of > 0.40) by single slice CT scan and/or biochemical evidence of metabolic syndrome as defined by ATP III criterial. These visceral fat values are based upon the data collected at Mayo Clinic using our methods, and are correlated with dyslipidemia and hyperinsulinemia.
• Female subjects are eligible if they meet the following criteria: are not pregnant or nursing; all women of childbearing potential will have a negative urine pregnancy test at screening and a negative urine pregnancy test within 48 hours before administering study drug; all women of childbearing potential will use an appropriate contraceptive method, including barrier method, oral contraceptive medication, contraceptive device or abstinence while participating in the study. They will confirm use of one of these methods.
• Recent or current research participation in a study that involves an investigational drug. Participants in other clinical trials that involve an investigational drug will not be able to participate in this study until 12 weeks after their participation in the other study is complete or > than five half-lives of the compound, whichever is longer: if Yes look at consent form and f/u visits: current use of medications that alter fatty acid or adipose metabolism possibly given: if yes, exclude;
• Amount of blood drawn during the study (if our study plus this one draw ≥ 450 ml these should be separated by 8 weeks.
• Previous labs: HbA1C < 6.5% for non-diabetic UBO; Fasting glucose < 126 mg/dl for non-diabetic UBO; Hb ≥ 11.0 for women and ≥ 12 for men; platelets > 100 000.

Exclusion Criteria:

• Individuals with a history of a disease process such as: ischemic heart disease; atherosclerotic valvular disease; persistent blood pressure greater than 160/95 despite antihypertensive medication.
• Smokers.
• Concomitant use of medications that can alter free fatty acid metabolism: high dose fish oil (>3g per day), (if yes, discontinue for 6 weeks); statins (if yes hold for 4 weeks and receive primary care provider's approval); Niacin; Fibrates; thiazolidinediones; Beta-blockers; Oral or injected corticosteroids or anabolic steroids; any history of use of pioglitazone; atypical antipsychotics.
• Allergy to lidocaine.
• Allergy to Niaspan documented by immunological testing.
• Allergy to indocyanine green.