Glycemic load, glycemic index and risk of cardiovascular diseases: Meta-analyses of prospective studies

doi:10.1016/j.atherosclerosis.2012.05.028

Atherosclerosis

Volume 223, Issue 2, August 2012, Pages 491-496

https://doi.org/10.1016/j.atherosclerosis.2012.05.028 Get rights and content

Abstract

Objective

The objective of this study was to assess the relations between glycemic load (GL), glycemic index (GI) and the risk of fatal or nonfatal cardiovascular diseases (CVDs).

Methods

Prospective studies were identified by a comprehensive search of Pubmed, ISI web of Science, the Cochrane Library and EMBASE database, supplemented with manual searches through the reference lists of original publications and review articles. Relative risks (RRs) and 95% confidence intervals (CIs) were extracted and pooled using a random-effect model, and dose–response meta-analysis was performed by the method of generalized least-squares.

Results

Fourteen studies were identified, involving 229,213 participants and more than 11,363 cases. The pooled RRs of CVDs risk for the highest vs lowest categories of GL and GI were 1.23 (95% CI: 1.11–1.36) and 1.13 (95% CI: 1.04–1.22) respectively. Both the risk estimates of GL and GI for women (GL: RR = 1.35, 95% CI: 1.18–1.55; GI: RR = 1.19, 95% CI: 1.06–1.34) were higher than men (GL: RR = 1.10, 95% CI: 0.95–1.28; GI: RR = 1.05, 95% CI: 0.94–1.17). No heterogeneity or publication bias was detected. Dose-response meta-analysis found an increased RR of 1.18 (95% CI: 1.01–1.38, P = 0.033) per 50 unit increment of GL with cardiac event risk in Caucasians.

Conclusions

High GL and GI were associated with significant increased risk of CVDs, specifically for women.

Highlights

► A comprehensive literature retrieval. ► Prospective design of the studies. ► High GL and GI were associated with significant increased risk of CVDs, specifically for women. ► Significant dose–response for the association of GL with CVDs. ► No heterogeneity or publication biases were detected.

Introduction

Cardiovascular diseases (CVDs) are the major cause of death worldwide. It was estimated that CVDs (I00–I99; Q20–Q28) accounted for 34.3% (831,272) of all 2426,264 deaths in 2006, or 1 of every 2.9 deaths in the United States [1]. High intake of carbohydrates can cause hyperglycemia which has been a well-established risk factor for cardiovascular disease, raise plasma fasting triacylglycerol primarily by enhancing hepatic synthesis of VLDL, and can also reduce HDL, thus creating an adverse lipid profile, then eventually increase the risk of CVDs [2], [3].

Carbohydrates with different physical forms, chemical structures, particle sizes, and fiber contents induce distinct plasma glucose and insulin responses, thus, glycemic index (GI), a measure of the average propensity of carbohydrate in the diet to increase blood glucose, and glycemic load (GL), which is calculated by multiplying the GI of a food with its carbohydrate content and represents both quality and quantity of carbohydrates, were introduced [4], [5].

Findings from prospective cohort studies have examined the association between GL, GI and CVDs risk, but results have been inconsistent. The aim of this study was to evaluate the evidence of prospective studies on GL, GI and CVDs risk by summarizing it quantitatively with a meta-analytic approach.

Section snippets

Literature search

The study was conducted based on guidelines proposed by Meta-analysis of Observational Studies in Epidemiology group (MOOSE) and the PRISMA Statement [6], [7]. We conducted a systematic literature search (up to October 2011) for publications using Pubmed, ISI web of Science, the Cochrane Library and EMBASE databases, and supplemented with manual searches through the reference lists of original publications and review articles. The following terms were included in the retrieval: (glycemic load

Literature search

A flow-chart showing the study selection procedure is presented in Fig. 1. A total of 3523 potentially publications were identified through the systematically retrieval of Pubmed, ISI web of Science, the Cochrane Library and EMBASE databases and manual searches of the reference lists of original publications and review articles. Of these, most of them were excluded for duplication retrieval or after scanning the title and abstract. We reviewed the full-texts of the 17 potential publications, of

Discussion

This meta-analysis of 14 prospective studies found that diets with a high GL or GI are associated with a respectively 23% and 13% increased risk of CVDs, respectively. Both the risk estimates of GL and GI for women were higher than men. Furthermore, a significant dose–response trend was detected for per 50 unit increment of GL with cardiac event risk in Caucasians, especially for coronary heart disease. To the best of our knowledge, this should be the most informative meta-analysis specifically

Conclusions

In summary, this meta-analysis provides strong evidence that significant increased associations existed between GL, GI and risk of CVDs. Given the high prevalence and incidence of CVDs in the general population, the observed associations between GL, GI and CVDs risk have clinical and public health importance. Future studies should attempt to assess whether these associations are causal and focus on the exact mechanisms through which GL or GI might affect the development and onset of CVDs.

Conflict of interest

None declared.

Acknowledgments

This study was supported by a grant from National Natural Science Foundation of China (No. 30871060).

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Refined grains are included as part of an unhealthy, or Western, dietary pattern, which has been shown to be associated with increased risk of cardiovascular disease (CVD). To clarify the association between refined grain intake and CVD risk, Pubmed and Scopus databases were searched for relevant cohort studies from database inception to June 30, 2022. Only studies that examined refined grains as a distinct consumption category and not as part of a dietary pattern, were included. Meta-analyses were performed using Cochrane's RevMan 5.4.1 software, applying inverse variance risk ratios in random effects models for each outcome of interest. Heterogeneity was assessed with Cochrane's Q (chi²) and I² statistics. Meta-analyses of hazard ratios (HR) and 95% confidence intervals (CI) obtained from 17 prospective cohort studies (>875,000 participants) indicated that refined grain intake was not associated with risk of CVD (HR = 1.08, 95% CI, 0.99-1.18, I² = 70%; 9 cohorts), stroke (HR = 1.06, 95% CI 0.92-1.23, I² = 70%; 9 cohorts), or heart failure (HR = 0.95, 95% CI 0.77-1.16, I² = 10%; 5 cohorts). White rice intake was also not associated with risk of CVD (HR = 0.93, 95% CI 0.86-1.00, I² = 25%; 7 cohorts) or stroke (HR = 1.03, 95% CI 0.93-1.14, I² = 22%; 7 cohorts). No significant publication bias was evident (Egger's test P values all > 0.05). The lack of association between refined grain intake and CVD risk was observed in meta-analyses of studies that restricted analyses to only staple grain foods (e.g., bread, cereal, pasta, white rice), as well as for meta-analyses of studies that included both staple and indulgent grain foods (e.g., cakes, cookies, doughnuts, brownies, muffins, pastries). Probable confounding from unmeasured variables in studies included in the meta-analyses diminishes the overall quality of evidence. Although refined grains are included as a component of the Western dietary pattern, the results of the meta-analyses suggest that refined grains do not contribute to the higher CVD risk associated with this unhealthy dietary pattern. This information should be considered in formulation of future dietary recommendations.
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Other sex-differences have also been observed in nutrition research. For example, lower carbohydrate quality (higher glycemic index and load) have been associated with stronger risk of type 2 diabetes and CVD in females compared to males [61,62]. Interestingly, sex differences have also been found with the effects of a Mediterranean diet, with men having better responses to the diet [63,64], similar to some of the findings in our study.
The Portfolio and Dietary Approaches to Stop Hypertension (DASH) diets have been shown to lower cardiometabolic risk factors in randomized controlled trials (RCTs). However, the Portfolio diet has only been assessed in RCTs of hyperlipidemic patients. Therefore, to assess the Portfolio diet in a population with metabolic syndrome (MetS), we conducted a longitudinal analysis of one-year data of changes in the Portfolio and DASH diet scores and their association with cardiometabolic risk factors in Prevención con Dieta Mediterránea (PREDIMED)-Plus trial.
PREDIMED-Plus is an ongoing clinical trial (Trial registration: ISRCTN89898) conducted in Spain that includes 6874 older participants (mean age 65 y, 48% women) with overweight/obesity fulfilling at least three criteria for MetS. Data for this analysis were collected at baseline, six months and one year. Adherence to the Portfolio and DASH diet scores were derived from a validated 143-item food frequency questionnaire. We used linear mixed models to examine the associations of 1-SD increase and quartile changes in the diet scores with concomitant changes in cardiometabolic risk factors.
After adjusting for several potential confounders, a 1-SD increase in the Portfolio diet score was significantly associated with lower HbA1c (β [95% CI]: −0.02% [−0.02, −0.01], P < 0.001), fasting glucose (−0.47 mg/dL [−0.83, −0.11], P = 0.01), triglycerides (−1.29 mg/dL [−2.31, −0.28], P = 0.01), waist circumference (WC) (−0.51 cm [−0.59, −0.43], P < 0.001), and body mass index (BMI) (−0.17 kg/m² [−0.19, −0.15], P < 0.001). A 1-SD increase in the DASH diet score was significantly associated with lower HbA1c (−0.03% [−0.04, −0.02], P < 0.001), glucose (−0.84 mg/dL [−1.18, −0.51], P < 0.001), triglycerides (−3.38 mg/dL [−4.37, −2.38], P < 0.001), non-HDL-cholesterol (−0.47 mg/dL [−0.91, −0.04], P = 0.03), WC (−0.69 cm [−0.76, −0.60 cm], P < 0.001), BMI (−0.25 kg/m² [−0.28, −0.26 kg/m²], P < 0.001), systolic blood pressure (−0.57 mmHg [−0.81, −0.32 mmHg], P < 0.001), diastolic blood pressure (−0.15 mmHg [−0.29, −0.01 mmHg], P = 0.03), and with higher HDL-cholesterol (0.21 mg/dL [0.09, 0.34 mg/dL, P = 0.001]). Similar associations were seen when both diet scores were assessed as quartiles, comparing extreme categories of adherence.
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Both dietary GI and GL shows the capability of a diet to induce postprandial glycaemia. These scores have been linked to a variety of chronic diseases in previous investigations [16–19,34]. However, very few observational studies have been conducted on the association between dietary GI and GL and risk of GDM [20,21].
This study aimed to investigate the association between dietary GI and GL and risk of GDM in a group of pregnant women in Iran.
A number of 812 pregnant women were recruited in their first trimester in a prospective study. A validated 117-item semi-quantitative food frequency questionnaire was used to assess usual dietary intakes of participants at study baseline. Dietary GI and GL were calculated based on earlier publications. GDM was diagnosed based on the results of a fasting plasma glucose concentration and a 50-g, 1-h oral glucose tolerance test at 24–28 weeks of gestation. Cox proportional hazards model was used to compute relative risks (RRs) and 95% confidence intervals (CI) for GDM.
Mean ± SD of age and BMI of study participants was 29.4 ± 4.84 y and 25.14 ± 4.08 kg/m², respectively at study baseline. Mean ± SD of dietary GI was 58 ± 7 and that of dietary GL was 176 ± 42. Overall, 28.4% (n = 231) of study population developed GDM at weeks 24–28 of pregnancy. After adjustment for potential confounding variables, we found that women in the highest tertile of dietary GL were 43% more likely to develop GDM than those in the lowest tertile (95% CI: 1.01, 2.00; P-trend = 0.03). However, no significant association was seen between dietary GI (RR for the highest tertile compared to the lowest: 0.85; 95% CI: 0.61, 1.20; P-trend = 0.37), and risk of GDM.
We found that women with the highest dietary GL were at a greater risk of developing GDM during pregnancy. No significant association was seen between dietary GI and risk of GDM.

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¹: M-XY and L-JP contributed equally to this article and should be considered as co-first authors.

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Glycemic load, glycemic index and risk of cardiovascular diseases: Meta-analyses of prospective studies

Abstract

Objective

Methods

Results

Conclusions

Highlights

Introduction

Section snippets

Literature search

Literature search

Discussion

Conclusions

Conflict of interest

Acknowledgments

J Am Coll Cardiol

Am J Clin Nutr

Control Clin Trials

Nutr Metab Cardiovasc Dis

Metabolism

Ann Epidemiol

Am J Clin Nutr

J Am Coll Cardiol

Am J Clin Nutr

Ann Epidemiol

Am J Clin Nutr

Metabolism

Am J Cardiol

Executive summary: heart disease and stroke statistics–2010 update: a report from the American heart association

Circulation

Dietary glycemic load and glycemic index and risk of coronary heart disease and stroke in Dutch men and women: the EPIC-MORGEN study

PLoS One