An Interdisciplinary Study of Eating Behavior in Twins

Scientists have recently discovered a number of hormones that control appetite and regulate weight. These hormones travel in the bloodstream and some of them change rapidly with every meal. They influence when we get hungry, how full we feel and probably even what foods taste good to us.  The main purpose of this study was to find out how genes and environmental factors contribute to the hormones controlling appetite and weight. This is an important area of research and may eventually help in finding new ways to help people avoid obesity or lose weight. A twin study was done  because it is the ideal way to study the relative contribution of genes and the environment to a health condition.

Twenty identical (MZ) female twin pairs were invited to participate in this study. The study consisted of a 24-hour (overnight) stay for both twins at the research unit of the University of Washington Medical Center.  At the beginning of the visit, an intravenous catheter (IV) was placed in the arm of each participant. This allowed nurses to take small blood samples from the IV at regular intervals over the next 24 hours. The blood samples were used to measure the levels of certain hormones in the blood, to see the pattern of change of hormone levels with meals.

At usual mealtimes, participants were given either a liquid meal (similar to a breakfast drink) or common foods to eat. They were asked to describe how the food tasted to them.

The following activities occurred during the visit:  A brief physical exam was performed. A DEXA scan (a special type of X-ray) was done to measure body composition. A resting metabolic rate study was done in the morning of the overnight stay. Participants were asked to fill out questionnaires that asked information about weight history and sleep and eating habits.

At the end of the overnight visit, some individual twins were asked to participate in the separate MRI part of the study. MRI scans were done for about 45 minutes. While in the scanner, the participant was asked to view and respond to photos of food and other objects.