Thermogenenic Responses to Fasting and Overfeeding in Women

Participants will complete a 3-day diet run-in followed by an 24-hr in-patient visit in the room calorimeter. The energy content of the diet will be REE x 1.5 (30% fat, 55% carbohydrate, 15% protein). On the study day, will arrive at 7 AM and an IV catheter will be placed for blood draws, as described in the research plan. Participants will then enter the calorimeter at 0800, exit at 0700 the following day. Participants will be instructed to engage in primary sedentary behaviors. The energy content of the diet will be 1.3 x REE (\~30% fat, 55% carbohydrate, and 15% protein at each meal). Breakfast will account for \~25% and lunch and dinner \~30-35% of total energy needs. Meals will be provided at 0900, 1300, and 1800, and a light snack will be provided at 2000.

Participants will complete a 3d diet run-in followed by an 24h in-patient visit in the room calorimeter. The energy content of the diet will be REE x 1.5 (30% fat, 55% carbohydrate, 15% protein). On the study day, will arrive at 7 AM and an IV catheter will be placed for blood draws, as described in the research plan. Participants will then enter the calorimeter at 0800, exit at 0700 the following day. Participants will be instructed to engage in primary sedentary behaviors. Participants will complete a 24 hour fast while in the calorimeter. They will be permitted to consume non-caloric beverages (i.e., water, non-caloric and non-caffeinated soft drinks, caffeine-free tea, or decaffeinated coffee) but refrain from consuming any caloric food or beverages. Upon exiting the calorimeter, participants will be provided a meal from the University of Colorado Hospital Patient Kitchen.

Participants will complete a 3d diet run-in followed by an 24h in-patient visit in the room calorimeter. The energy content of the diet will be REE x 1.5 (30% fat, 55% carbohydrate, 15% protein). On the study day, will arrive at 7 AM and an IV catheter will be placed for blood draws, as described in the research plan. Participants will then enter the calorimeter at 0800, exit at 0700 the following day. Participants will be instructed to engage in primary sedentary behaviors. The energy content of the diet will be 200% of energy requirements, based on EE measured during the eucaloric condition. Macronutrient intake will be 3% protein, 51% carbohydrate, and 46% fat. Breakfast will account for \~25% and lunch and dinner \~30-35% of total energy needs. Meals will be provided at 0900, 1300, and 1800, and a light snack will be provided at 2000.