Full Papers

Human and Clinical Nutrition

Soya protein does not affect glycaemic control in adults with type 2 diabetes

Colleen P. Gobert^a1, Elizabeth A. Pipe^a1, Sarah E. Capes^a2, Gerarda A. Darlington^a3, Johanna W. Lampe^a4 and Alison M. Duncan^a1 c1

^a1 Department of Human Health and Nutritional Sciences, University of Guelph, Guelph, Ont., Canada N1G 2W1

^a2 Vancouver Island Health Authority, Vancouver, BC, Canada V8R 1J8

^a3 Department of Mathematics and Statistics, University of Guelph, Guelph, Ont., Canada N1G 2W1

^a4 Fred Hutchinson Cancer Research Center, Seattle, WA 98109, USA

Abstract

Evidence from observational, animal and human studies supports a role for soya protein and its isoflavones in the improvement of glycaemic control in type 2 diabetes. The objective of the present study was to determine the effect of isoflavone-rich soya protein on markers of glycaemic control in adults with type 2 diabetes. Using a randomised, crossover, double-blind, placebo-controlled design, adults with diet-controlled type 2 diabetes (n 29) consumed soya protein isolate (SPI) and milk protein isolate (MPI) for 57 d each separated by a 4-week washout. Blood was collected on days 1 and 57 of each treatment period for analysis of fasting HbA1C, and fasting and postprandial glucose, insulin and calculated indices of insulin sensitivity and resistance. Urine samples of 24 h were collected at the end of each treatment period for analysis of isoflavones. Urinary isoflavone excretion was significantly greater following consumption of SPI compared with MPI, and 20·7 % of the subjects (n 6) were classified as equol excretors. SPI consumption did not significantly affect fasting or postprandial glucose or insulin, fasting HbA1C, or indices of insulin sensitivity and resistance. These data do not support a role for soya protein in the improvement of glycaemic control in adults with diet-controlled type 2 diabetes and contribute to a limited literature of human studies on the effects of soya protein on the management of type 2 diabetes.

(Received March 18 2009)

(Revised July 21 2009)

(Accepted July 27 2009)

(Online publication August 26 2009)

Key Words:

• Soya protein;
• Isoflavones;
• Type 2 diabetes;
• Glycaemic control

Correspondence:

^c1 Corresponding author: Alison M. Duncan, fax +1 519 763 5902, email amduncan@uoguelph.ca

Footnotes

Abbreviations: AUC, area under the curve; C_max, maximum concentration; HOMA-IR, homeostasis model assessment of insulin resistance; ISI_Matsuda, insulin sensitivity index-Matsuda; log, logarithm; QUICKI, quantitative insulin sensitivity check index; MPI, milk protein isolate; SPI, soya protein isolate; T_max, time to C_max