Postprandial Nutrient Homeostasis Before and After Weight Loss Induced by Low-calorie Diet or RYGB

The purpose of this study is to compare the metabolic responses to low-carbohydrate and standard-carbohydrate meals in African Americans and non-Hispanic White adults with obesity and the effect of weight loss induced by low-calorie diet (LCD) or Roux-en-Y gastric bypass (RYGB) on the metabolic responses to low-carbohydrate and standard meals. Participants will consume: 1) a standard-carbohydrate meal (\~49 g glucose) and 2) a low-carbohydrate (\~3.4 g glucose) meal on separate study visits performed in a randomized order. We will evaluate the meals' effect before and after \~16-18% weight loss on postprandial i) insulin kinetics, ii) glucose kinetics iii) β-cell function; iv) plasma triglyceride and non-esterified fatty acid concentrations; v) plasma hormone concentrations; vi) plasma cytokine concentrations; vi) plasma metabolomics; and vii) adipose tissue transcriptomics.

Inclusion Criteria: Surgery Group (RYGB): * Males and Females * Scheduled for RYGB surgery * Body Mass Index 35-60 kg/m² * Without Type 2 Diabetes (T2D) LCD group: * Males and Females * Body Mass Index 35-60 kg/m² * Without Type 2 Diabetes (T2D) Exclusion Criteria: * Regular use of tobacco products * Previous intestinal resection * Pregnant or breastfeeding * Evidence of significant organ system dysfunction or disease other than obesity and T2D * Use of any medication that might, in the opinion of the investigator, affect metabolic function * Exercise ≥90 minutes per week * Use or past use of hormone replacement therapy within the past 6 months