The effect of underfeeding for 7 d (at 60 kJ/kg ideal body-weight) on the thermic and physiological responses to glucose and insulin infusions (hyperinsulinaemic euglycaemic clamp) was studied in six healthy women. Underfeeding had no significant effect on baseline metabolic rate, heart rate, forearm blood flow, diastolic blood pressure, blood intermediary metabolites, plasma insulin or catecholamines, but reduced both respiratory exchange ratio (RER; control (C) 0.86 (SE 0.02), underfed (U) 0.75 (SE 0.01) P < 0.01) and systolic blood pressure (by approximately 10 mmHg, P < 0.01). Baseline forearm glucose uptake and oxygen consumption were similar in both states. During the final 30 min of the glucose and insulin infusion, metabolic rate rose by 0.43 (SE 0.05) kJ/min in the C state, but no rise was seen in the U state (P < 0.01). Glucose disposal rate (C 47.9 (SE 1.8), U 47.3 (SE 4.1) μmol/kg per min) and storage rate (C 27.5 (SE 2.4), U 31.6 (SE 3.6) μmol/kg per min) were similar in both states, but glucose oxidation rate was reduced in the U state (C 20.5 (SE 1.7), U 15.4 (SE 0.7) μmol/kg per min; P < 0.05). RER rose to a higher value in the C state than in the U state (C 0.97 (SE 0.2), U 0.80 (SE 0.01); P < 0.01). During hyperinsulinaemia, the forearm glucose uptake and O2 consumption rose in both states. No significant differences were seen in the cardiovascular responses to hyperinsulinaemia in either state. Thus underfeeding abolishes the rise in thermogenesis and reduces glucose oxidation during glucose and insulin infusions in healthy women, but does not affect the glucose disposal or storage rates or the other measured responses.
