Total energy expenditure (TEE) is comprised of the following components: resting energy expenditure (REE), thermic effect of food intake (TEF), adaptive thermogenesis (AT). The thermic effect of food is the amount of energy expended to digest food, and can be affected by factors such as protein / fat / carbohydrate contents of meals or the amount of time over which a meal is consumed. The investigators propose to assess the contributions of the thermic effect of food intake (TEF), which is the amount of energy expended to digest food, to overall energy expenditure in CF. Participants will be assigned to either a high fat liquid meal or a high protein liquid meal and assessed for components of energy expenditure in the whole room indirect calorimeter (metabolic chamber); participants will then be crossed over to the alternate liquid meal type, and differences in resting and total energy expenditure and the thermic effect of food will be assessed between the two types of meals.
The investigators propose to assess the contributions of the thermic effect of food intake (TEF), which is the amount of energy expended to digest food, to overall energy expenditure in Cystic Fibrosis (CF).