After providing consent, subjects will undergo an indirect calorimetry test, which involves breathing through a disposable, single-use mouth piece into a machine that estimates calorie needs based on oxygen consumed and CO2 produced. Then subjects will be instructed on how to keep a 3-day food record and complete the Qualtrics survey designed for this purpose within 2 weeks of consenting. Nutrient content of the participants' typical diet will be calculated, based on the 3-day and Qualtrics-based food/beverage log, using Food Processor software. Meals for the acclimation period will be created to mimic the participants' typical diet (daily calories and percent of calories from carbohydrate, protein and fat), as well as to meet their calorie needs per the indirect calorimeter test, for the first 7-9 days of the study. High protein diets (2g of protein/kg/day) will then be devised and provided for the next 14-16 days. Following this period, reduced protein diets (0.8g of protein/kg/day) will be devised and provided for the next 14-16 days. Fat content will be modulated to keep diets isocaloric while keeping carbohydrate content stable. Participants will choose between two 3-day cycle menus for each feeding phase. Meals will be prepared in a metabolic kitchen housed in SBU's Business Incubator at Calverton. Meals will be prepared in batches, packaged and frozen at the incubator, then transported in a cooler with thermometers to the Food Service Department at SBU Hospital. Meals will be kept frozen in freezers until the day they are provided to participants. Logs of temperatures of coolers will be maintained daily, with temperatures checked every hour.

In order to provide meals, participants will come to the feeding site to eat breakfast onsite and pick up other meals and snacks for the rest of the day. Participants will be provided a closed envelope containing a form that will list their participant ID# and age in which they'll sign in and indicate if they've begun any new medications or been diagnosed with a disease since starting the study. Additionally, twice per week, participants will be weighed using a digital scale in order to track changes in body weight while on the study. If weight changes greater than 2% of baseline, calorie content of the meals will be modified to avoid further weight changes. Food for the rest of the day will be provided in an insulated bag containing frozen cold packs and participants will be instructed to keep lunch and dinner in the insulated bag or a refrigerator until eaten. They will be instructed to heat the respective meals in a microwave until hot, prior to consumption. They will be instructed to take a picture of each meal before and after eating and upload the pictures via a Qualtrics-based survey, in order for the investigators to estimate how much food has been eaten at each meal. Although participants will be instructed to only eat the food and beverages provided for the study, they will log any consumption of food or beverages not provided for the study via this same Qualtrics-based survey. Consumption of water, black coffee and tea will not be logged.

During days 7-9, 24-26 and 41-43 participants will provide a stool sample to be placed into a sterile container (provided by the study team) then placed into an opaque brown paper bag and provided to the study team. At the same time the stool sample is delivered, blood will be drawn to generate serum. If a participant provides samples in the earlier part of the collection period (e.g. day 7) they will proceed immediately to the next phase of the study.