The effects of fat and protein on glycemic responses in nondiabetic humans vary with waist circumference, fasting plasma insulin, and dietary fiber intake

J Nutr. 2006 Oct;136(10):2506-11. doi: 10.1093/jn/136.10.2506.


The effects of protein and fat on glycemic responses have not been studied systematically. Therefore, our aim was to determine the dose-response effects of protein and fat on the glycemic response elicited by 50 g glucose in humans and whether subjects' fasting plasma insulin (FPI) and diet influenced the results. Nondiabetic humans, 10 with FPI < [corrected] or =40 pmol/L and 10 with FPI >40 pmol/L, were studied on 18 occasions after 10 14-h overnight fasts. Subjects consumed 50 g glucose dissolved in 250 mL water plus 0, 5, 10, or 30 g fat and/or 0, 5, 10, or 30 g protein. Each level of fat was tested with each level of protein. Dietary intake was measured using a 3-d food record. Gram per gram, protein reduced glucose responses approximately 2 times more than fat (P < 0.001) with no significant fat x protein interaction (P = 0.051). The effect of protein on glycemic responses was related to waist circumference (WC) (r = -0.56, P = 0.011) and intake of dietary fiber (r = -0.60, P = 0.005) but was unrelated to FPI or other nutrient intakes. The effect of fat on glycemic responses was related to FPI (r = 0.49, P = 0.029) but was unrelated to WC or diet. We conclude that, across the range of 0-30 g, protein and fat reduced glycemic responses independently from each other in a linear, dose-dependent fashion, with protein having approximately 3-times the effect of fat. A large protein effect was associated with high WC and high dietary-fiber intake, whereas a large fat effect was associated with low FPI. These conclusions may not apply to solid meals. Further studies are needed to determine the mechanisms for these effects.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Adolescent
  • Adult
  • Anthropometry*
  • Blood Glucose / analysis*
  • Cholesterol / blood
  • Cholesterol, HDL / blood
  • Cholesterol, LDL / blood
  • Dietary Fats / pharmacology*
  • Dietary Fiber / administration & dosage*
  • Dietary Proteins / pharmacology*
  • Fasting
  • Female
  • Homeostasis
  • Humans
  • Insulin / blood*
  • Insulin Resistance
  • Male
  • Middle Aged
  • Triglycerides / blood


  • Blood Glucose
  • Cholesterol, HDL
  • Cholesterol, LDL
  • Dietary Fats
  • Dietary Fiber
  • Dietary Proteins
  • Insulin
  • Triglycerides
  • Cholesterol