Like all animals, humans have to regulate energy usage or “metabolic rate” to perform functions. The food we take in provides us with fuel. In my laboratory, we have built specialized instruments that can accurately measure how many calories we use by measuring the air we breathe. From these studies, we can determine the amount of energy needed for resting or physical activities, and where the energy comes from. Energy can come from either fat or carbohydrates. We are also interested in studying how environmental factors, such as changes in environmental temperature, can alter our metabolic rates and other basic body functions, such as heart rate and muscle activities.