The Role of Protein in Regulating Ad Libitum Energy Intake in Humans

The purpose of this project is to determine if protein is less likely to create positive energy balance when added to the diet compared to carbohydrate. To do this, the investigators will take detailed measurements of participant's baseline metabolic rate to understand their energy requirements. Then, the investigators will feed participants all their meals for two weeks, Monday-Friday, and measure their food intake. During one of the week-long feeding periods, participants will consume a shake made of egg protein that is \~20% of their energy requirements. During the other week, participants will consume a shake made of carbohydrate that is \~20% of their energy requirements. Participants will drink the assigned shake at the beginning of each of their daily three meals, and then they will be offered a 'regular' meal of unlimited quantity. Participants will not know that the investigators are measuring the food consumed after drinking the shake. Participants will drink the protein shake for the first week and carb-based shake for the second week, and vice versa-- depending on the randomization order. To account for energy expenditure, participants will wear an activity monitor, an accelerometer. Energy balance, measured as participant energy intake minus energy expenditure, will be our main outcome for each treatment. However, because participants may change their behavior if made aware of the true research question, the investigators will tell participants that the purpose of the study is to see how low fiber and high fiber shakes affect mood. The hypothesis is that during the week when participants consume the protein shake, they will remain in energy balance, but during the week of carbohydrate shake consumption, participants will have positive energy balance.