Utilization of protein, carbohydrate, and fat in fasting and postabsorptive subjects.

Energy expenditure, carbohydrate, protein, fat utilization, as well as metabolic water production were evaluated in ten healthy adult volunteers in fasting and postabsorptive states. The values of the nonprotein respiratory quotient established whether the fasting or postabsorptive relationship was used in the computer program. After ingestion of a 900 kcal mixed meal, significant increases were observed for energy metabolism (P less than 0.01), carbohydrate utilization (P less than 0.001), and water production (P less than 0.001). The calculated lipid values suggested that fat was being synthesized in the postabsorptive state (P less than 0.001). No significant changes in protein utilization were found.