Systematic review
Long-term effects of low glycemic index/load vs. high glycemic index/load diets on parameters of obesity and obesity-associated risks: A systematic review and meta-analysis

https://doi.org/10.1016/j.numecd.2013.04.008Get rights and content

Abstract

Aim

The aim of the present meta-analysis was to investigate the long-term effects of glycemic index-related diets in the management of obesity with a special emphasis on the potential benefits of low glycemic index/load (GI/GL) in the prevention of obesity-associated risks.

Data synthesis

Electronic searches for randomized controlled trials (RCTs) comparing low glycemic index/load versus high glycemic index/load diets were performed in MEDLINE, EMBASE and the Cochrane Library. Outcome of interest markers included anthropometric data as well as biomarkers of CVD and glycemic control. Study specific weighted mean differences were pooled using a random effect model. 14 studies were included in the primary meta-analysis. Weighted mean differences in change of C-reactive protein [WMD: −0.43 mg/dl, (95% CI −0.78 to −0.09), p = 0.01], and fasting insulin [WMD: −5.16 pmol/L, (95% CI −8.45 to −1.88), p = 0.002] were significantly more pronounced in benefit of low GI/GL diets. However decrease in fat free mass [WMD: −1.04 kg (95% CI −1.73 to −0.35), p = 0.003] was significantly more pronounced following low GI/GL diets as well. No significant changes were observed for blood lipids, anthropometric measures, HbA1c and fasting glucose. Sensitivity analysis was performed for RCTs excluding subjects with type 2 diabetes. Decreases in C-reactive protein and fasting insulin remained statistically significant in the low GI/GL subgroups.

Conclusions

The present systematic review provides evidence for beneficial effects of long-term interventions administering a low glycemic index/load diet with respect to fasting insulin and pro-inflammatory markers such as C-reactive protein which might prove to be helpful in the primary prevention of obesity-associated diseases.

Introduction

The concept of the glycemic index (GI) was developed by Jenkins and colleagues in 1981 for management of glycemic control in patients with type 2 diabetes mellitus (T2D) [1]. The GI ranks the carbohydrate content of individual foods according to their postprandial glycemic effects expressed as a percentage of the response to an equivalent carbohydrate portion of a reference food such as 50 g of glucose. In 1997, the term glycemic load (GL) was introduced to quantify the overall glycemic effect of food with respect to its specific carbohydrate content in typically consumed quantities [2], [3], [4]. Diets with a special focus on GI/GL are usually recommended for individuals with overweight and obesity and/or patients with T2D. According to data of the World Health Organization, approximately 1.5 billion adults are considered to be either obese or overweight [5]. Besides T2D, several other metabolic disorders are known to be associated with obesity, e.g. hypertension, dyslipidemia, metabolic syndrome, and cardiovascular disease [6]. Provided that GI/GL diets represent both an effective and efficient means for weight management and glycemic control, they would represent a valuable tool in the primary and secondary prevention of these disorders. In fact, a recent meta-analysis of cohort studies showed a decreased relative risk of coronary heart disease comparing the lowest with the highest GI/GL quintile in women, but not in men [7]. Various meta-analyses of randomized controlled trials (RCTs) investigated the effects of diets with low GI/GL (LGI/LGL) as compared to high GI/GL (HGI/HGL) dietary regimens in overweight, obesity, and T2D [8], [9], [10], [11], [12], [13], [14]. In addition, high dietary GI and GL are associated with acute myocardial infarction in the Kuopio Ischemic Heart Disease Risk Factor [15]. Although a number of beneficial effects of LGI/LGL diets could be observed, most RCTs considered in the systematic reviews were short-term studies thus limiting the validity of interpretations of long-term performance of low GI protocols. Indications for a prolonged salutary effect of LGI/LGL diets were provided by a meta-analyses of prospective cohort studies reporting a significant inverse correlation between GI/GL and risk of T2D [16]. The aim of the present systematic review was to investigate the long-term (≥6 months) effects of LGI/LGL as a dietary means in the management of overweight and obesity with special emphasis on its potential usability in the primary prevention of obesity-associated disorders.

Section snippets

Literature search

Queries of literature were performed using the electronic databases MEDLINE (between 1966 and February 2013), EMBASE (between 1980 and February 2013), and the Cochrane Trial Register (until February 2013) with restrictions to randomized controlled trials, but no restrictions to language and calendar date using the following search term: (glycemic index; glycemic load), taking variant spelling of search terms into consideration (i.e. glycaemic index; glycaemic load). Moreover, the reference

Literature search

Altogether, 15 studies extracted from 2170 articles met the inclusion criteria, and 14 of them were included in the quantitative analysis [24], [25], [26], [27], [28], [29], [30], [31], [32], [33], [34], [35], [36], [37]. The paper by Raatz et al. [38] reported no appropriate follow-up data and was considered for qualitative analysis only. The detailed steps of the meta-analysis article selection process are described as a flow diagram in Fig. 2.

Study characteristics

All studies included were RCTs with a duration ranging between 24 and 68 weeks, published between 2005 and 2011 and enrolling a total of 2344 participants (65% women, 35% men). General study characteristics are summarized in (Supplementary Information Tables 1, 2).

Since type 2 diabetes mellitus (T2D) was not defined as an exclusion criteria, four studies included subjects with T2D [25], [26], [27], [32]. In the LGI/LGL groups, the range for glycemic index was 30–76, while glycemic load varied

Discussion

The present meta-analysis investigated the effects of glycemic index/load on parameters of body composition and biomarkers of cardiovascular risk in long-term dietary intervention studies with overweight and obese subjects. In summary, decreases in C-reactive protein, fasting insulin and fat free mass were significantly more pronounced in the LGI/LGL diet groups as compared to their HGI/HGL counterparts, while all other parameters under investigation were affected in a comparable fashion. Thus,

Conflict of interest

The authors declare to have no conflict of interest.

Acknowledgments

The authors are grateful to Susan Jebb, PhD and Thomas Wolever, PhD, for providing the raw data of their original studies for this meta-analysis.

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