"Current guidelines for intensive treatment of type 1 diabetes base the mealtime insulin bolus calculation exclusively on carbohydrate counting."True. It varies but one unit of insulin usually covers 15 grams of carbohydrate.
"There is strong evidence that free fatty acids impair insulin sensitivity."There is. See my past posts.
"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."To test their hypothesis they fed patients meals with identical carbohydrate and protein content but different fat content (10 grams vs. 60 grams).
Their results supported their hypothesis:
"High-fat dinner required more insulin than low-fat dinner (12.6 ± 1.9 units vs. 9.0 ± 1.3 units; P = 0.01) and, despite the additional insulin, caused more hyperglycemia."So, a meal that contained 60 grams of fat required 42% more insulin than a meal that contained 10 grams of fat. (In a crossover design, you lessen interindividual effect - how different people metabolize macronutrients differently. This increases the validity of their finding.)
Even though high-fat eaters injected more insulin, which is supposed to clear their blood of excess glucose, they had higher blood glucose than the low-fat eaters who used less insulin - for the same carbs.