Low glycaemic index diet and disposition index in type 2 diabetes (the Canadian trial of carbohydrates in diabetes): a randomised controlled trial.
OBJECTIVE
We recently found that oral glucose tolerance over 1 year in type 2 diabetic patients declined to a significantly lesser degree on a low-glycaemic-index than on a reduced-carbohydrate diet. Here, we examined whether that finding was associated with an improvement in disposition index, an index of beta cell function defined as the product of insulin sensitivity and insulin secretion. Since this is a report of secondary analysis on a previously published trial, the results should be considered as hypothesis-generating.


METHODS
Type 2 diabetic patients treated by diet alone (n = 162) were randomised by computer to high-carbohydrate/high-glycaemic index (High-GI, n = 52), high-carbohydrate/low-glycaemic index (Low-GI, n = 56) or low-carbohydrate/high-monounsaturated-fat (Low-CHO, n = 54) diets for 1 year in a multi-centre, parallel-design clinical trial conducted at University teaching hospitals. At baseline and at 3, 6 and 12 months participants underwent 75 g OGTTs; 27 participants dropped out or were excluded. Indices of insulin sensitivity, insulin secretion and disposition index, derived from the OGTT, were compared among diets. Those assessing the outcomes were blinded to group assignment.


RESULTS
Neither muscle insulin sensitivity index nor insulinogenic index differed significantly among diets. However, a significant time x diet interaction existed for disposition index (muscle insulin sensitivity index x insulinogenic index) (p = 0.036). After 3 months, disposition index tended to be higher on Low-CHO than on Low-GI diets, namely by 0.07 h(-1) (95% CI -0.04, 0.18). However, by 12 months this reversed and disposition index became higher on Low-GI than on Low-CHO, namely by 0.12 h(-1) (0.01, 0.23; p < 0.05, baseline disposition index 0.23 h(-1)). There were no important adverse effects associated with the treatments.


CONCLUSIONS
These results suggest that, in patients with type 2 diabetes on diet alone, a Low-GI diet for 1 year increases disposition index, an index of beta cell function, compared with a Low-CHO diet.
Wolever
T M S
TM
Department of Nutritional Sciences, 150 College St, Toronto, ON, Canada, M5S 3E2. thomas.wolever@utoronto.ca
Mehling
C
C
Chiasson
J-L
JL
Josse
R G
RG
Leiter
L A
LA
Maheux
P
P
Rabasa-Lhoret
R
R
Rodger
N W
NW
Ryan
E A
EA
D015992:Body Mass Index; D049628:Body Size; D002170:Canada; D003924:Diabetes Mellitus, Type 2 / Q000178:diet therapy*; D003927:Diet, Diabetic; D005260:Female; D006442:Glycated Hemoglobin / Q000378:metabolism; D038321:Glycemic Index; D006339:Heart Rate; D006801:Humans; D008297:Male; D008875:Middle Aged; D010045:Outpatients
D006442:Glycated Hemoglobin