Dietary fat acutely increases glucose concentrations and insulin requirements in patients with type 1 diabetes: implications for carbohydrate-based bolus dose calculation and intensive diabetes management

Abstract

Objective: Current guidelines for intensive treatment of type 1 diabetes base the mealtime insulin bolus calculation exclusively on carbohydrate counting. There is strong evidence that free fatty acids impair insulin sensitivity. We hypothesized that patients with type 1 diabetes would require more insulin coverage for higher-fat meals than lower-fat meals with identical carbohydrate content.

Research design and methods: We used a crossover design comparing two 18-h periods of closed-loop glucose control after high-fat (HF) dinner compared with low-fat (LF) dinner. Each dinner had identical carbohydrate and protein content, but different fat content (60 vs. 10 g).

Results: Seven patients with type 1 diabetes (age, 55 ± 12 years; A1C 7.2 ± 0.8%) successfully completed the protocol. HF dinner required more insulin than LF dinner (12.6 ± 1.9 units vs. 9.0 ± 1.3 units; P = 0.01) and, despite the additional insulin, caused more hyperglycemia (area under the curve >120 mg/dL = 16,967 ± 2,778 vs. 8,350 ± 1,907 mg/dL⋅min; P < 0001). Carbohydrate-to-insulin ratio for HF dinner was significantly lower (9 ± 2 vs. 13 ± 3 g/unit; P = 0.01). There were marked interindividual differences in the effect of dietary fat on insulin requirements (percent increase significantly correlated with daily insulin requirement; R(2) = 0.64; P = 0.03).

Conclusions: This evidence that dietary fat increases glucose levels and insulin requirements highlights the limitations of the current carbohydrate-based approach to bolus dose calculation. These findings point to the need for alternative insulin dosing algorithms for higher-fat meals and suggest that dietary fat intake is an important nutritional consideration for glycemic control in individuals with type 1 diabetes.

Figure 1

Closed-loop glucose control periods (shaded) starting with LF and HF dinners (10 vs. 60 g) with identical carbohydrate and protein content, and ending after identical breakfast meals. Each closed-loop period was preceded by an open-loop period with identical lunch meals and similar activity.

Figure 2

Top: Venous plasma glucose levels during the two 18-h periods of closed-loop insulin delivery (from 6:00 p.m. until 12:00 p.m.) after the LF diet (LFD) dinner compared with HF diet (HFD) dinner. Middle: Insulin delivery during the closed-loop control. Bottom: Insulin concentration (Conc) during the closed-loop control. *Significant (P < 0.05) difference in paired data.

Figure 3

Top: Glucose AUC >120 mg/dL (AUC_>120). Middle: Total insulin delivered. Bottom: Insulin AUC. Time Period, indicates clock time. *P < 0.05; **P < 0.01; ****P < 0.0001.