Table 1

Summary of systematic review: effects of fat, protein, and GI on acute postprandial glycemia in type 1 diabetes

Nutritional factorSummary of findingsClinical implications
Fat• Seven studies (total 103 subjects) (5,7,8,11,15,18,19).
• All studies reported significant differences in glycemia with addition of fat.
• Fat reduces early glucose response (first 2–3 h) (7,8) and delays peak blood glucose (5,7,15,18) due to delayed gastric emptying.
• Fat leads to late postprandial (>3 h) hyperglycemia (18,19).
• Addition of 35 g fat can increase blood glucose by 2.3 mmol/L (15), and in some individuals, 50 g of fat can increase insulin requirements by twofold (19).
• Marked interindividual differences in the glycemic effect of fat.• Increase in dose required for coverage of higher-fat meals needs to be individualized.
• Delicate balance in calculation and timing of insulin action: needs more insulin to prevent late postprandial hyperglycemia; however, if too much insulin upfront, there is a risk for early postprandial hypoglycemia.
Protein• Seven studies (total 125 subjects) (5,8,11,13,1517).
• All studies reported significant differences in glycemia with addition of protein.
• Effect of protein is delayed (effects seen ∼100 min postmeal) (11,13,15,17).
• Protein has different effects when consumed with and without carbohydrates [e.g., 30 g protein with carbohydrates will affect blood glucose (15,16), whereas at least 75 g protein is needed to see an effect when consumed in isolation (13)].• Protein-only meals (e.g., ≥230 g lean steak with salad) may require a different insulin dosing strategy than for protein and carbohydrate meals.
GI• Seven studies (total 98 subjects) (4,6,810,12,14).
• All studies reported significant differences in glycemia with differing GI (same carbohydrate).
• High-GI foods have rapid glucose spike (9,14).
• Low-GI foods lower overall glucose response (810,12,14), reduce glucose peak (4,9,14), and increase risk of hypoglycemia (when usual CIR is used) (6,9,10).• Mismatch between insulin action and carbohydrate absorption following high-GI foods can be problematic, leading to a rapid glucose spike.
• Total carbohydrate content still important: a large carbohydrate serving of low-GI food will still cause large glycemic response.
• Low-GI foods with high fructose and/or sucrose content (e.g., fruit juice) will still produce a rapid glucose spike.