The glycemic, insulinemic and plasma amino acid responses to equi-carbohydrate milk meals, a pilot- study of bovine and human milk

Abstract

Background: Dairy proteins, in particular the whey fraction, exert insulinogenic properties and facilitate glycemic regulation through a mechanism involving elevation of certain plasma amino acids, and stimulation of incretins. Human milk is rich in whey protein and has not been investigated in this respect.

Method: Nine healthy volunteers were served test meals consisting of human milk, bovine milk, reconstituted bovine whey- or casein protein in random order. All test meals contributed with 25 g intrinsic or added lactose, and a white wheat bread (WWB) meal was used as reference, providing 25 g starch. Post-prandial levels in plasma of glucose, insulin, incretins and amino acids were investigated at time intervals for up to 2 h.

Results: All test meals elicited lower postprandial blood glucose responses, expressed as iAUC 0-120 min compared with the WWB (P < 0.05). The insulin response was increased following all test meals, although only significantly higher after whey. Plasma amino acids were correlated to insulin and incretin secretion (iAUC 0-60 min) (P ≤ 0.05). The lowered glycemia with the test meals (iAUC 0-90 min) was inversely correlated to GLP-1 (iAUC 0-30 min) (P ≤ 0.05).

Conclusion: This study shows that the glycemic response was significantly lower following all milk/milk protein based test meals, in comparison with WWB. The effect appears to originate from the protein fraction and early phase plasma amino acids and incretins were involved in the insulin secretion. Despite its lower protein content, the human milk was a potent GLP-1 secretagogue and showed insulinogenic properties similar to that seen with reconstituted bovine whey-protein, possibly due to the comparatively high proportion of whey in human milk.

Figures

Figure 1

Incremental changes in plasma glucose and serum insulin. Mean incremental changes (Δ) in plasma glucose (A) and serum insulin (B) in response to equal amounts of carbohydrate. In (C) the GI and II (iAUC) are displayed. For plasma glucose a significant treatment effect (p < 0.0002) and time × treatment interaction (p < 0.0265) were found at a given time. Values with different lowercase letters are significantly different, p ≤ 0.05 (Tukey’s test). n = 9 healthy subject.

Figure 2

Incremental changes in plasma GIP and GLP-1. Mean incremental changes (Δ) in plasma GLP-1 (A) and GIP (B) in response to equal amounts of carbohydrate. Significant treatment effects (p < 0.001) as well as time × treatment interactions (p < 0.001) were found for both GLP-1 and GIP. Values with different letters are significantly different, p < 0.05 (Tukey’s test). n = 8 (WWB, whey) and n = 7 (human milk, casein).