In a study of patients with type 1 diabetes, Joslin researchers observed that dietary fat and free fatty acids (FFAs) impair insulin sensitivity and increase glucose production.

Seven participants (adults with type 1 diabetes with an average age of 55) successfully completed the study. They spent two days at Beth Israel Deaconess Medical Center eating carefully controlled meals and having their glucose and insulin levels monitored.

Study results showed that participants required more insulin after eating the high-fat dinner than the low-fat dinner (12.6 units compared to 9 units). In contrast, the two breakfast meals required similar insulin doses. Despite the increased insulin, participants had greater hyperglycemia after the high-fat dinner with insulin levels elevated five to ten hours after the meal. The average increase in insulin was 42 percent with significant individual differences. "These findings highlight the limitations of basing mealtime insulin dosing for type 1 diabetes solely on carbohydrate intake," says Dr. Wolpert (lead author Howard Wolpert, MD, Senior Physician in the Joslin Clinic Section on Adult Diabetes and the Director of the Insulin Pump Program at Joslin). "We need to consider fat as well as carbohydrates in insulin dosing calculations as well as in nutritional recommendations."