Thermic Effect of Feeding in Cystic Fibrosis

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).

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 changes in energy expenditure measured in kcal (resting energy expenditure prior to feeding, and thermic effect of food after meal administration) will be recorded in the metabolic chamber.

blood glucose (mg/dL) measured with continuous glucose sensor and fasting venous sample at end of study visit

Inclusion Criteria: confirmed diagnosis of cystic fibrosis by Cystic Fibrosis Foundation-established criteria being followed at the VCU (Virginia Commonwealth University) Adult Cystic Fibrosis Center pulmonary and overall health status at baseline as assessed by pulmonary function testing and screening labs (complete blood count, liver enzymes, cholesterol, HgA1c). Criteria for baseline status are established for each individual patient as part of routine CF pulmonary care. ability to understand the study procedures and to comply with them for the entire length of the study Exclusion Criteria: experiencing any signs or symptoms consistent with a pulmonary exacerbation (a decline in pulmonary function testing from baseline, recorded as part of routine CF care) undergoing treatment for a pulmonary exacerbation with a change in antibiotics or steroids from their baseline medications tobacco users pregnancy