Relationship between changes in GIP concentrations and changes in insulin and C-peptide concentrations after guar gum therapy

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Abstract
In order to elucidate the mechanisms of the action of gel-forming fibre in diabetes, we measured insulin, C-peptide and GIP responses to meals during treatment with guar gum and placebo in normal and non-insulin-dependent diabetic (NIDD) subjects. Dietary supplementation with guar gum caused a sustained reduction of the GIP response in normal and diabetic subjects (p<0.05), but did not influence insulin responses. On the other hand, guar gum increased the C-peptide response to meals in normal subjects (p<0.05) resulting in a 40% decrease of the insulin/C-peptide ratio (p<0.01). Assuming that the insulin/C-peptide ratio reflects the hepatic extraction of insulin, this would be compatible with increased hepatic removal of insulin. The change in insulin/C-peptide ratio was positively correlated with the change in GIP response after guar gum (r = 0.75; p<0.001) and this correlation was strengthened in normal subjects (r=0.91; p<0.001). Our data thus suggest that guar gum stimulates rather than suppresses insulin secretion. The apparent insulinotropic action of GIP may partly be explained by a reduced hepatic extraction of insulin.