Before participants engage in the overeating part of the study, researchers will measure their body fat and will conduct a test to make sure they don't have diabetes or impaired glucose tolerance. Then, scientists will count how many calories the participants burn in a day while they're studied. This measurement is done in a respiratory chamber where the amount of oxygen taken in and carbon dioxide expelled is monitored, revealing the number of calories burned.
"Some people might be able to burn off more excess calories as heat when they overeat, so they are the people more likely to be thin," said Marie Thearle, a staff clinician involved in the study. "We are also asking our volunteers to come back for follow-up visits once a year for up to seven years to see if any of the energy expenditure measurements with overeating during the baseline study visit predict who gains weight over time and who does not."
Thearle hopes to look deeper still into how different bodies use different nutrients, such as carbohydrates, fat and protein, and if food choices matter. "We measure whether the participant's body prefers to use carbohydrates or fat for fuel, and then we further break this down to see how many calories are being used from carbohydrates, fat and protein, respectively."
Thearle says the researchers hope to find out whether food choices matter. "Once you have met the needs of your body, does it matter what else you consume?" she said. "There's the popular myth that people don't gain weight because they have a high metabolism; we want to see if that is true. We will be looking at hormones and brown fat. We don't think the answer is differences in metabolism." Brown fat is the "good" fat that scientists say helps burn calories — and white fat, or what we think of as regular fat.