, Glycemic Load and risk: a meta-analysis

A Barclay1, P Petocz2, V Flood1,3, J McMillan-Price1, T Prvan2, J Brand-Miller1 1.Human Nutrition Unit, University of Sydney, NSW, 2006, Australia. 2. Department Department of Statistics, Macquarie University, NSW, 2109, Australia. 3. NSW Centre for Public Health Nutrition, University of Sydney, NSW, 2006, Australia

1. BackgroundBackground Inconsistent findings from observational studies have prolonged the controversy over the effects of dietary glycemic index (GI) and glycemic load (GL) and the risk of developing type 2 diabetes.

2. ObjectiveObjective To evaluate the association between GI, GL and the risk of diabetes using meta-analysis of prospective cohort studies.

3. DesignDesign Medline, EMBASE, CINAHL and the Cochrane Library databases were searched for the period Jan 1981 – March 2007. From 8 prospective cohort studies identified, 422,224 women and men were followed up for 4 to 9 years. Data on study design, characteristics of participants, and dietary assessment tools utilized, were independently abstracted by 2 investigators using a standardized protocol. Studies were stratified further according to the validity of the tools used to assess dietary intake. Rate Ratios (RR) were estimated in a Cox proportional hazards model and combined using a random effects model.

4. ResultsResults A total of 5,891 incident cases of diabetes were identified. For comparison between highest versus lowest quantile of GI (High GI median = 59; Low GI median = 45; = 100) and GL (High GL median = 134; Low GL median = 85), a significant positive association was found in fully-adjusted models (GI RR=1.20, 95% Confidence Interval (CI), 1.04-1.38; GL RR=1.16, 95% CI, 1.01-1.34). 4.4. ResultsResults (continued…) (continued)… The association increased when the 2 studies that had poor validity (correlation between Frequency Questionnaire and other dietary assessment method <0.5) were excluded from the analysis, leaving a total of 3,302 cases out of 376,707 people (GI RR=1.39, 95% CI, 1.23-1.57; GL RR=1.25, 95% CI, 1.10-1.41) (Figures 1 and 2). These associations are equal to or greater than those observed for wholegrains (20-30%) and diabetes risk1.

Figure 1. Rate ratio estimates for fully-adjusted models investigating the association between GI and the risk of developing type 2 diabetesMeta-analysis (validated of studies Low GIonly). studies - Type 2 diabetes

Model Group by Study name Statistics for each study Rate ratio and 95% CI Dis Rate Lower Upper ratio limit limit Z-Value p-Value Type 2 diab SalmeronF 1.37 1.09 1.72 2.74 0.01 Type 2 diab SalmeronM 1.37 1.02 1.84 2.11 0.03 Type 2 diab Schulze 1.59 1.21 2.09 3.30 0.00 Type 2 diab Hodge 1.36 0.95 1.95 1.68 0.09 Type 2 diab Zhang 1.30 1.00 1.68 1.98 0.05 Fixed Type 2 diab 1.39 1.23 1.57 5.33 0.00 Random Type 2 diab 1.39 1.23 1.57 5.33 0.00 0.1 0.2 0.5 1 2 5 10

Favours high GI Favours low GI

Adjusted GI - validated studies only 5. Conclusion Figure 2. Rate ratio estimates for fully-adjusted models investigating the association between GL and the risk of developing type 2 Meta-analysisdiabetes (validated of studiesLow GI only). studies - Type 2 diabetes

Model Group by Study name Statistics for each study Rate ratio and 95% CI Low glycemic Dis Rate Lower Upper index and ratio limit limit Z-Value p-Value glycemic load Type 2 diab SalmeronF 1.47 1.16 1.86 3.20 0.00 Type 2 diab SalmeronM 1.25 0.90 1.73 1.34 0.18 diets are Type 2 diab Schulze 1.33 0.92 1.92 1.53 0.13 Type 2 diab Hodge 0.91 0.52 1.59 -0.33 0.74 independently Type 2 diab Zhang 1.61 1.02 2.54 2.06 0.04 associated with Type 2 diab Patel07c 1.15 1.06 1.25 3.32 0.00 Fixed Type 2 diab 1.19 1.11 1.28 4.79 0.00 reduced risk of Random Type 2 diab 1.25 1.10 1.41 3.53 0.00 type 2 diabetes. 0.1 0.2 0.5 1 2 5 10

FavoursFavours high High GL GIFavours Favours lowLow GL GI

6. Reference Adjusted GL - validated studies only

1. Venn BJ, Mann JI. Cereal grains, legumes and diabetes. Eur Clin Nutr 2004;58:1443-61.