Elsevier

Nutrition

Volume 31, Issue 3, March 2015, Pages 437-442.e2
Nutrition

Review
The effect of glucomannan on body weight in overweight or obese children and adults: A systematic review of randomized controlled trials

https://doi.org/10.1016/j.nut.2014.09.004Get rights and content

Highlights

  • Glucomannan (GM), a soluble fiber, is marketed as being helpful in reducing body weight, but data supporting this claim are scarce.

  • Systematic search was performed up to June 2014 for randomized controlled trials assessing the effectiveness of GM in reducing body weight and body mass index.

  • GM may help to reduce body weight, but not body mass index, in otherwise healthy overweight or obese adults.

  • Data in children are too limited for any conclusions to be drawn.

Abstract

Objective

Glucomannan (GM), a soluble fiber derived from the plant Amorphophallus konjac, is marketed as being helpful in reducing body weight. However, the data supporting this claim are scarce. The aim of this review was to systematically evaluate the effects of GM on body weight (BW) and body mass index (BMI) in otherwise healthy obese or overweight children and adults.

Methods

MEDLINE, EMBASE, CENTRAL, and Google Scholar databases were systematically searched up to June 2014 for randomized controlled trials (RCTs) assessing the effectiveness of GM versus placebo. The primary outcome measures were BW and BMI.

Results

Six eligible RCTs, only one of which performed in children, were included. In adults, three RCTs reported a significant reduction in BW in the GM group compared with the control group at the following different points during the intervention: At week 2 (mean difference [MD], 0.21 kg; 95% confidence interval [CI], 0.13–0.29); at week 4 (MD, 2.04; 95% CI, 0.52–3.56); at week 5 (MD, 1.3; 95% CI, 0.89–1.71); and at week 8 (MD, 3.17; 95% CI, 1.29–5.05). Only one RCT reported a beneficial effect at more than one point. None of the RCTs reported a favorable effect of GM on BMI.

Conclusions

In otherwise healthy overweight or obese adults, there is some evidence that in the short term GM may help to reduce BW, but not BMI. Data in children are too limited to draw any conclusions.

Introduction

The prevalence of obesity is reaching epidemic proportions. The first-line treatment (i.e., promoting a healthy diet and regular physical activity) is difficult to follow. There is continuous research into the modalities complementing lifestyle modifications that are helpful in the reduction of body weight (BW). Due to the prevalent use of over-the-counter products advertised as being effective in promoting weight loss, evidence is needed to confirm the claimed effects. One of the dietary supplements used is glucomannan (GM), a soluble fiber derived from the plant Amorphophallus konjac. Its potential mechanism of action is to increase satiety due to a delay in gastric empting caused by the “mass effect” of the viscous, gel-like mass forming in the stomach and slowing down gastrointestinal transit time [1]. In 2010, the European Food Safety Authority (EFSA) confirmed the positive effect of GM on the reduction of BW in overweight adults. The effect was achieved when ≥3 g of GM was supplemented daily in three doses of 1 g together with one to two glasses of water before a meal. However, at that time, the EFSA did not confirm the effect in children [2]. Similarly, an expert panel sponsored by the U.S. National Heart, Lung, and Blood Institute stated that “glucomannan does not significantly improve weight loss” in children [3].

In many European countries, GM is being widely marketed for the management of overweight or obesity. Given the scarcity of data and somewhat conflicting recommendations, we decided to conduct a randomized controlled trial (RCT) assessing the weight loss effect of GM supplementation in children. However, as previously noted, a systematic review of the literature should precede the conducting of new research [4].

A systematic search has been conducted to evaluate the clinical effectiveness of supplementation with GM; the researchers concluded that it beneficially affected total cholesterol, low-density lipoprotein cholesterol, triglycerides and BW, but not high-density lipoprotein cholesterol or blood pressure [5]. As more than 5 y have passed since that review was published, we aimed to systematically evaluate the current evidence on the effect of GM supplementation on BW reduction as our main point of interest. We aimed to exclude studies referring to patients with diabetes mellitus, hypertension, or other chronic conditions requiring drug treatment. This decision was made to better define the effect of GM supplementation in the population we aimed to address in the planned interventional trial (i.e., obese or overweight, otherwise healthy individuals).

Section snippets

Review protocol

The methods planned at each stage of this review were specified in advance and documented. However, formally, the review protocol was not registered.

Criteria for eligibility

Participants had to be children or adults who were overweight/obese (according to our definition). To increase the homogeneity, we decided not to include studies performed in populations with predefined diabetes mellitus or hyperglycemia, as well as in other populations with diagnosed diseases requiring drug treatment. All studies that assessed the

Search results and characteristics of studies

Figure 1 presents a flowchart documenting the study selection process. Two registered studies were identified in clinicaltrials.gov (one ongoing and one of unknown status); for their characteristics, see Supplementary Table 1. The Table summarizes the key characteristics of the six included trials (RCTs). Five studies are of parallel design [8], [9], [10], [11], [12] and one is a crossover design [13]. The participants included were children (one RCT, N = 60) [10] and adults (five RCTs,

Principal findings

The objective of this review was to update evidence on the effect of GM supplementation on BW compared with administration of a placebo. A statistically significant reduction in BW was observed in three studies. In the first one, the transient effect was seen after 2 wk, but it did not last until the end of the 8-wk intervention [9]. Another study, on the contrary, reported a significant difference between groups in BW reduction in favor of GM after both 4 and 8 wk of treatment [12]. An effect

Conclusion

In overweight or obese, otherwise healthy adults, there is limited evidence that GM supplementation may help to reduce BW, but not BMI. Limited data do not allow one to draw any conclusions with regards to the effect of GM supplementation in children.

Studies of proper methodological design, consisting of larger study groups with longer (>12 wk) interventions and follow-up periods, are needed, especially in children, to establish whether the BW-reducing potential of GM is clinically significant.

References (17)

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This study was fully funded by the Medical University of Warsaw. HS was responsible for the study concept and supervision. BMZ and AC were responsible for acquisition and analysis and interpretation of data, as well as for drafting of the first draft of the manuscript. All the authors took part in the study design and critical revision of the manuscript for important intellectual content. The authors have no conflicts of interest to report.

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