Glycemic index, glycemic load, and chronic disease risk--a meta-analysis of observational studies.

Human Nutrition Unit, University of Sydney, Sydney, Australia.
American Journal of Clinical Nutrition (Impact Factor: 6.92). 04/2008; 87(3):627-37.
Source: PubMed

ABSTRACT Inconsistent findings from observational studies have prolonged the controversy over the effects of dietary glycemic index (GI) and glycemic load (GL) on the risk of certain chronic diseases.
The objective was to evaluate the association between GI, GL, and chronic disease risk with the use of meta-analysis techniques.
A systematic review of published reports identified a total of 37 prospective cohort studies of GI and GL and chronic disease risk. Studies were stratified further according to the validity of the tools used to assess dietary intake. Rate ratios (RRs) were estimated in a Cox proportional hazards model and combined by using a random-effects model.
From 4 to 20 y of follow-up across studies, a total of 40 129 incident cases were identified. For the comparison between the highest and lowest quantiles of GI and GL, significant positive associations were found in fully adjusted models of validated studies for type 2 diabetes (GI RR = 1.40, 95% CI: 1.23, 1.59; GL RR = 1.27, 95% CI: 1.12, 1.45), coronary heart disease (GI RR = 1.25, 95% CI: 1.00, 1.56), gallbladder disease (GI RR = 1.26, 95% CI: 1.13, 1.40; GL RR = 1.41, 95% CI: 1.25, 1.60), breast cancer (GI RR = 1.08, 95% CI: 1.02, 1.16), and all diseases combined (GI RR = 1.14, 95% CI: 1.09, 1.19; GL RR = 1.09, 95% CI: 1.04, 1.15).
Low-GI and/or low-GL diets are independently associated with a reduced risk of certain chronic diseases. In diabetes and heart disease, the protection is comparable with that seen for whole grain and high fiber intakes. The findings support the hypothesis that higher postprandial glycemia is a universal mechanism for disease progression.

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    ABSTRACT: Aim: To compare the cumulative (three-day) effect of prolonged sitting on metabolic responses during a mixed meal tolerance test (MTT), with sitting that is regularly interrupted with brief bouts of light-intensity walking. Research design and methods: Overweight/obese adults (n=19) were recruited for a randomized, three-day, outpatient, crossover trial involving: 1) 7-hour days of uninterrupted sitting (SIT); and, 2) 7-hour days of sitting with light-intensity activity breaks [BREAKS; 2-minutes of treadmill walking (3.2 km/hour) every 20 minutes (total: 17 breaks/day)]. On days 1 and 3, participants underwent a MTT (75g carbohydrate, 50g fat), and the incremental area under the curve (iAUC) was calculated from hourly blood samples. GEE models were adjusted for gender, BMI, energy intake, treatment order and pre-prandial values to determine effects of time, condition and time x condition. Results: The glucose iAUC was 1.3 ± 0.5 and 1.5 ± 0.5 (mean difference ± SEM) higher in SIT compared with BREAKS on days 1 and 3 respectively (condition effect: P=0.001), with no effect of time (P=0.48) or time x condition (P=0.8). The insulin iAUC was also higher on both days in SIT (Day 1: ∆151 ± 73, Day 3: ∆91 ± 73, P=0.01), with no effect of time (P=0.52) or time x condition (P=0.71). There was no between-treatment difference in triglycerides iAUC. Conclusion: There were significant between-condition effects but no temporal change in metabolic responses to MTT, indicating that breaking up sitting over three days sustains, but does not enhance, the lowering of postprandial glucose and insulin.

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