Objective: Ingestion of a mixed meal recruits flow to muscle capillaries and increases total forearm blood flow in healthy young lean people. We examined whether these vascular responses are blunted by obesity.
Research design and methods: We fed eight middle-aged lean and eight obese overnight-fasted volunteers a liquid mixed meal (480 kcal). Plasma glucose and insulin were measured every 30 min, and brachial artery flow and muscle microvascular recruitment (contrast ultrasound) were assessed every 60 min over 2 h after the meal.
Results: By 30 min, plasma glucose rose in both the lean (5.1 +/- 0.1 vs. 6.7 +/- 0.4 mmol/l, P < 0.05) and the obese groups (5.4 +/- 0.2 vs. 6.7 +/- 0.4 mmol/l, P < 0.05). Plasma insulin rose (28 +/- 4 vs. 241 +/- 30 pmol/l, P < 0.05) by 30 min in the lean group and remained elevated for 2 h. The obese group had higher fasting plasma insulin levels (65 +/- 8 pmol/l, P < 0.001) and a greater postmeal area under the insulin-time curve (P < 0.05). Brachial artery flow was increased at 120 min after the meal in the lean group (38 +/- 6 vs. 83 +/- 16 ml/min, P < 0.05) but not in the obese group. Muscle microvascular blood volume rose by 120 min in the lean group (14.4 +/- 2.2 vs. 24.4 +/- 4.2 units, P < 0.05) but not in the obese group.
Conclusions: A mixed meal recruits muscle microvasculature in lean subjects, and this effect is blunted by obesity. This impaired vascular recruitment lessens the endothelial surface available and may thereby impair postprandial glucose disposal.