Insulin requirements for meals were measured in eight insulin-dependent diabetic patients, using a closed-loop insulin infusion system. Patients required more insulin for breakfast than for an isocaloric lunch (35.7 ± 5.5 mU/kcal/3 h versus 26.9 ± 5.1 mU/kcal/3 h, P < 0.02) or an isocaloric supper (35.7 ± 5.5 mU/kcal/ 3 h versus 26.6 ± 6.6 mU/kcal 3 h, P = 0.05). To determine whether this insulin resistance at breakfast might be due to low basal insulin levels overnight, the insulin needs for breakfast were compared after an overnight fast (day 1) and after a midnocturnal (0200 h–0500 h) insulin infusion (day 2). Breakfast insulin requirements were similar on both days (35.7 ± 5.5 mU/kcal/3 h versus 37.7 ± 5.1 mU/kcal/3 h, P = NS).

Whereas nonobese diabetic patients required approximately 60% more insulin for breakfast than for other meals, obese diabetic patients in this study did not demonstrate insulin resistance at breakfast.

These findings provide a basis for the common clinical practice of allocating more insulin for breakfast than for other meals. The absence of an increased insulin need at breakfast in our obese patients cautions against a similar algorithm for obese diabetic patients. We postulate that growth hormone may be a cause for morning insulin resistance.

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