FIGURE 1.

Study day protocol. The experimental diets were given as hourly meals for 8 h. Priming doses of NaH¹³CO₃ and L-[1–¹³C]phenylalanine were given with the fifth meal; hourly doses of L-[1–¹³C]phenylalanine were given with meals 5 through 8. Three breath samples were collected prior to the tracer protocol. Six plateau breath samples were collected after the tracer protocol. One venous blood sample was collected after the sixth hourly meal. Carbon dioxide production rate (VCO₂) was measured by indirect calorimetry after the fifth hourly meal. A fasting blood glucose measurement and a urine sample were taken before the first meal.