Hindawi Publishing Corporation

Journal of Obesity
Volume 2013, Article ID 610908, 7 pages
http://dx.doi.org/10.1155/2013/610908

Clinical Study
Safety and Efficacy of Glucomannan for Weight Loss in
Overweight and Moderately Obese Adults

Joyce K. Keithley,1 Barbara Swanson,1 Susan L. Mikolaitis,2 Mark DeMeo,3

Janice M. Zeller,4 Lou Fogg,5 and Jehan Adamji6
1
Rush University College of Nursing, 600 S. Paulina Street, Suite 1080, Chicago, IL 60612, USA
2
Rush University Medical Center, 1725 W. Harrison Street, Chicago, IL 60612, USA
3
Section of Gastroenterology and Nutrition, Rush University Medical Center, 1725 W. Harrison Street, Chicago, IL 60612, USA
4
North Park University School of Nursing, 3225 W. Foster Avenue, Chicago, IL 60625, USA
5
Community, Systems, and Mental Health Nursing, Rush University College of Nursing, 600 S. Paulina Street, Suite 1080,
Chicago, IL 60612, USA
6
Faculty Practice, Rush University College of Nursing, 600 S. Paulina Street, Suite 1080, Chicago, IL 60612, USA

Correspondence should be addressed to Joyce K. Keithley; joyce k keithley@rush.edu

Received 4 September 2013; Revised 10 December 2013; Accepted 12 December 2013

Academic Editor: Jordi Salas-Salvadó

Copyright © 2013 Joyce K. Keithley et al. This is an open access article distributed under the Creative Commons Attribution
License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly
cited.

Background. Few safe and effective dietary supplements are available to promote weight loss. We evaluated the safety and efficacy
of glucomannan, a water-soluble fiber supplement, for achieving weight loss in overweight and moderately obese individuals
consuming self-selected diets. Methods. Participants were randomly assigned to take 1.33 grams of glucomannan or identically
looking placebo capsules with 236.6 mL (8 ounces) of water one hour before breakfast, lunch, and dinner for 8 weeks. The
primary efficacy outcome was change in body weight after 8 weeks. Other efficacy outcomes were changes in body composition,
hunger/fullness, and lipid and glucose concentrations. Safety outcomes included gastrointestinal symptoms/tolerance and serum
liver enzymes and creatinine levels. Results. A total of 53 participants (18–65 years of age; BMI 25–35 kg/m2 ) were enrolled and
randomized. The two groups did not differ with respect to baseline characteristics and compliance with the study supplement. At 8
weeks, there was no significant difference between the glucomannan and placebo groups in amount of weight loss (−.40 ± .06 and
−.43 ± .07, resp.) or other efficacy outcomes or in any of the safety outcomes. Conclusions. Glucomannan supplements administered
over 8 weeks were well tolerated but did not promote weight loss or significantly alter body composition, hunger/fullness, or lipid
and glucose parameters. This trial is registered with NCT00613600.

1. Introduction are needed. One potentially promising alternative approach

is glucomannan, a dietary supplement widely promoted and
Overweight and obesity are exceedingly difficult to reverse. used for its weight loss properties. Despite its widespread
Despite the widespread use of conventional management use, the safety and efficacy of glucomannan have not been
strategies—low-calorie diets, physical activity, behavioral adequately studied.
interventions, and pharmacological agents—the prevalence Glucomannan is a water-soluble, fermentable dietary
of overweight and obesity continues to rise in the US. fiber extracted from the tuber or root of the elephant yam,
An estimated 65% of all US adults were either overweight also known as konjac (Amorphophallus konjac or Amor-
or obese during 2007-2008 [1]. Overweight and obesity phophallus rivieri). Glucomannan consists of a polysaccha-
increase the risk for comorbidities such as diabetes and ride chain of beta-D-glucose and beta-D-mannose with
atherosclerosis and are associated with reduced quality of attached acetyl groups in a molar ratio of 1 : 1.6 with beta 1–
life and life expectancy [2, 3]. Clearly, alternative approaches 4 linkages (see Figure 1) [4–6]. Because human salivary and
2 Journal of Obesity

CH2 OH 6 CH OCOCH CH2 OH CH2 OH

2 3
O 5 O O O
H H H H
H H 1 H H
O 4 O O O
OH H OH H OH HO OH HO
H H H H
3 2
H OH H OH H H H H

Glucose Glucose with Mannose Mannose

acetate group
on carbon 6

Figure 1: Structure of a segment of glucomannan with repeating glucose and mannose units.

pancreatic amylase cannot split beta 1, 4 linkages, glucoman- currently using fiber supplements or had intolerance to fiber
nan passes relatively unchanged into the colon, where it is supplements, had untreated/unstable metabolic conditions
highly fermented by colonic bacteria. It has a high molecular known to influence weight status (e.g., hypothyroidism, type
weight (average: 1,000,000 Daltons) and can absorb up to 50 2 diabetes mellitus), had gastrointestinal disorders that might
times its weight in water, making it one of the most viscous cause complications or influence motility or satiety (e.g.,
dietary fibers known [6]. Therefore, glucomannan is taken in diverticulitis, inflammatory bowel disease, irritable bowel
smaller doses than other types of fiber supplements. syndrome, intestinal narrowing or obstruction, and diffi-
The mechanisms that mediate the weight reduction culty swallowing), were using medications or complementary
effects of glucomannan are thought to be similar to those and alternative medicine (CAM) therapies that might affect
of other water-soluble, fermentable fibers. With its low weight or food absorption (e.g., diuretics, glucocorticoids,
energy density and bulking properties, glucomannan seems anorexigenic agents, Orlistat, acupuncture, and Hoodia), had
to promote weight loss by displacing the energy of other an eating disorder, or were participating in a weight loss
nutrients and producing satiety and satiation as it absorbs program. Other exclusion criteria were stage II hypertension
water and expands in the gastrointestinal tract. In addition, (≥160/100 mmHg) or dyslipidemia (fasting LDL cholesterol ≥
glucomannan seems to reduce total cholesterol and low- 160 mg/dL; total cholesterol ≥ 240 mg/dL; triglycerides >
density lipoprotein (LDL) cholesterol levels by stimulating 200 mg/dL; HDL ≤ 40 mg/dL), fasting serum glucose >
fecal excretion of cholesterol and bile acids and decreasing 126 mg/dL, renal or liver disease, history of depression, abuse
intestinal absorption of cholesterol [7–9]. Also, glucomannan of illicit drugs or alcohol, use of cigarettes, or pregnant, less
may improve glycemic parameters by inhibiting appetite than 6 months postpartum, or lactating.
and slowing intestinal absorption due to increased viscosity Based on a previous placebo-controlled trial of gluco-
[10–13]. Glucomannan is generally well tolerated and has a mannan [18], we planned to recruit 50 participants and follow
favorable safety profile. them up for 8 weeks to have 80% power to adequately detect
Glucomannan has been associated with reductions in changes in weight and other metabolic variables.
body weight and plasma lipid and glucose levels in adults in a
few clinical trials [14–19]. But these trials have been limited by 2.2. Study Design. Eligible individuals who consented to par-
weak designs, small sample sizes, heterogeneous diagnoses, ticipate in the study were randomly assigned to receive cap-
variable formulations and dosages of glucomannan, and short sules containing glucomannan or a matching placebo filled
duration of follow-up [20]. In contrast to these studies, with inactive microcrystalline cellulose. A random number
we used a randomized, double-blind, placebo-controlled generator was used to create a randomization sequence;
design to evaluate the safety and efficacy of 3.99 g/day of boxes containing each participant’s supply of capsules were
glucomannan capsules in a sample of 53 healthy overweight packaged according to this sequence. Both the glucomannan
and moderately obese adults consuming self-selected diets and placebo capsules were prepared by an external pharmacy,
and maintaining usual physical activity levels during an 8- which had no other role in the study. To ensure that the
week study period. glucomannan supplement used during the study period met
quality control standards, it was purchased from the same
lot, and a sample was submitted to ConsumerLab.com for
2. Materials and Methods
compositional and purity analyses, which indicated appropri-
2.1. Study Population. Men and women were recruited from ate composition and purity. Neither the participants nor the
a clinic within an urban academic medical center, located investigators were aware of the treatment assignments.
in a Health Resources and Services Administration (HRSA) Participants were instructed to take two 666 mg (1.33 g)
designated medically underserved area. Individuals were glucomannan or placebo capsules with 236.6 mL (8 oz.) of
eligible for inclusion in the study if they were between the ages water one hour before breakfast, lunch, and dinner for 8
of 18 and 65 years and had body mass index (BMI) ≥25 and weeks (for a total of 3.99 g/day). They were also encouraged
≤35 at study entry. Individuals were not eligible if they were to maintain their current dietary intake and physical activity
Journal of Obesity 3

levels. Study participants returned at 2 weeks and 8 weeks weeks and analyzed using NutriBase clinical data analy-
to return any unused study supplement or placebo from the sis software (http://www.nutribase.com/). The International
previous visit, receive a new supply of the study supplement Physical Activity Questionnaire (IPAQ) [24] was adminis-
or placebo for the remaining 6 weeks, report on side effects, tered at baseline, 2 weeks and 8 weeks to characterize any
and have blood drawn. changes in usual activity level during the study period that
All data were collected by study research personnel and could affect study outcomes. Supplement compliance was
uploaded to TeleForm (electronic scanning) database by measured by capsule counts and self-report of percentage
a research assistant. The study was approved by the site of capsules taken. Calculated compliance was defined as the
institutional review board. All participants provided written percentage of prescribed doses taken from baseline through
informed consent before enrollment. An independent data the 8-week study period. Since differences in participants’
and safety monitoring committee monitored the trial and perceptions of credibility of the treatment rationale and their
reviewed the interim results. expectancy could confound the findings, we administered the
credibility/expectancy Questionnaire (CEQ) to participants
2.3. Primary Outcome. The primary efficacy outcome was in both groups on the first and last days of the treatment [25].
weight loss from baseline to 2 weeks and 8 weeks after
randomization. Body weight was measured to the nearest 2.5. Statistical Analysis. All statistical analyses were per-
1/10 kg using a calibrated electronic scale, with participants formed with SPSS 16.0 (Chicago, IL). Descriptive statistics
wearing light clothing without shoes [21]. were used to characterize the sample. Nominal data were
analyzed by the use of the chi-square test, whereas contin-
2.4. Secondary Outcomes. Secondary efficacy outcomes in- uous data were analyzed by the use of Pearson’s correlation
cluded changes in body composition (waist/hip circumfer- analyses, independent sample 𝑡-tests, and one-way analysis of
ence, body fat, and fat-free mass), hunger and fullness, and variance. The data are presented as mean ± SD. A significance
fasting lipids and blood glucose parameters. Waist and hip level of 0.05 was determined a priori.
circumference were determined using standardized proce-
dures [22] and body fat and fat-free mass were measured 3. Results
using Tanita Ultimate Scale (Tanita Corp., Tokyo, Japan).
Subjective sensations of hunger and fullness were assessed 3.1. Study Population. Figure 2 depicts the screening, enroll-
using standardized 100 mm visual analog scales (VAS) [23]. ment, and follow-up of participants in the trial. Of the 124
The hunger scale was anchored by the words, “Not at all adults screened, a total of 53 met eligibility criteria and
hungry” and “Extremely hungry” and the fullness scale was were enrolled in the study. Twenty-six participants were
anchored by “Not at all full” and “Extremely full.” Participants randomly assigned to the glucomannan group and twenty-
were asked to make a vertical mark across the line corre- seven participants to the placebo group. There were no
sponding to their feelings during the past four hours on the significant differences between the two groups in rates of
day of their scheduled clinic visit (total = three days during discontinuation. Three participants in each group were either
the 8-week study period). To score the scales, the distance lost to follow-up or discontinued the study for personal
in mm from 0 for each scale was measured with a ruler. reasons, resulting in a final sample of 47 participants.
Fasting peripheral venous blood specimens were obtained for Baseline demographic and clinical characteristics were
glucose and lipid levels. A standard lipid panel was used to similar between the two groups (Table 1). Participants were
quantify triglycerides, total cholesterol, and HDL cholesterol; predominately female (∼85%), represented a mix of racial
LDL cholesterol levels were calculated using the Friedewald and ethnic groups, and had a mean age of 40.6 years. For
equation. the 47 participants who completed the study, the calculated
Key safety outcomes were gastrointestinal symptoms and compliance was 81.3% ± 4.5% in the glucomannan group and
tolerability and laboratory assessment of liver and renal 82.7% ± 5% in the placebo group.
function. Gastrointestinal symptoms and tolerance were
determined by asking participants about difficulty swallow- 3.2. Study Outcomes. For the primary outcome, there was no
ing, abdominal distention, diarrhea, belching, and other significant difference in the amount of weight loss between
gastrointestinal-related symptoms using standard methods of the participants in the glucomannan group and those in the
nondirected questioning, including when symptoms started placebo group at either two weeks (−.32 ± .04 and −.11 ±
and whether they were thought to be related to the study .02, resp.) or eight weeks (−.40 ± .06 and −.43 ± .07, resp.)
supplement. Liver enzymes were considered elevated with an after randomization (Table 2). Results of secondary efficacy
aspartate aminotransferase level >275 u/L and/or an alanine outcomes are also shown in Table 2. There were no significant
transferase >250 u/L; for serum creatinine, a level > 4.5 mg/dL differences in body composition measures, hunger/fullness,
was considered elevated. and fasting lipid and glucose levels. Belching (13.4% versus
Other measures included dietary intake, physical activity, 4.1%), bloating (12.7% versus 3.7%), and stomach fullness
supplement compliance, and credibility/expectancy percep- (11.9% versus 2.4%) occurred more frequently in partici-
tions of the study treatment. To assess for changes over the pants on glucomannan than those on placebo, but these
8-week study period, dietary intake was measured using symptoms were transient, lasting for only 1-2 hours after
3-day food records completed at baseline, 2 weeks, and 8 taking glucomannan on the first 1–3 study days, and did
4 Journal of Obesity

124 screened for eligibility

53 eligible and randomized

26 randomized to intervention 27 randomized to placebo

23 completed study 24 completed study

lost to follow-up (n = 1); discontinued lost to follow-up (n = 2); discontinued
study (n = 2, personal reasons) study (n = 1, personal reasons)

23 included in analysis 24 included in analysis

Figure 2: Study flow diagram.

Table 1: Baseline demographic and clinical characteristics of study participants (𝑁 = 47).

Characteristic: 𝑛 (%) Glucomannan (𝑛 = 23) Control (𝑛 = 24)

Gender
Male 3 (13%) 4 (16.7%)
Female 20 (87%) 20 (83.3%)
Race/ethnic group
White 9 (39.1%) 13 (54.2%)
Black 8 (34.8%) 6 (25.0%)
Hispanic 4 (17.4%) 5 (20.8%)
Other 2 (8.6%) 0 (0%)
Characteristic: mean (±SD)
Age, years 35.59 (12.21) 41.59 (10.08)
Height, ft/in 5.42 (.41) 5.50 (.30)
Weight, kg 83.27 (12.32) 85.36 (12.41)
Body mass index, kg/m2 30.70 (2.86) 30.91 (3.28)
Waist circumference, cm 94.92 (10.25) 96.73 (11.03)
Hip circumference, cm 112.99 (8.05) 113.45 (7.41)
Fat mass, kg 32.93 (2.43) 31.91 (2.37)
Fat-free mass, kg 51.99 (3.51) 50.71 (3.61)
Total cholesterol, mg/dL 209.20 (41.82) 204.29 (31.04)
LDL cholesterol, mg/dL 135.95 (33.41) 129.76 (27.03)
HDL cholesterol, mg/dL 40.45 (8.49) 53.24 (12.50)
Triglycerides, mg/dL 123.40 (61.26) 106.90 (27.67)
Fasting glucose, mg/dL 87.05 (10.35) 86.00 (11.29)

not lead to study discontinuation. Hepatic and renal safety 4. Discussion

outcomes remained normal throughout the study and did not
significantly differ between the control and treatment groups. In our study, supplementation with glucomannan did not
Other measures, including dietary intake, physical activity, result in significant weight loss at either 2 or 8 weeks after
supplement compliance, and credibility/expectancy, also did randomization. Also, there was no evidence of benefit of
not differ significantly between the groups. glucomannan supplementation with respect to any of the
Journal of Obesity 5

Table 2: Effects of glucomannan on efficacy outcomes (𝑁 = 47).

Glucomannan (𝑛 = 23) Control (𝑛 = 24)

Characteristic: mean
Baseline 2 weeks 8 weeks Baseline 2 weeks 8 weeks
Weight, kg 83.75 83.43 83.36 85.4 85.3 84.97
Weight loss, kg — −.32 −.40 — −.11 −.43
2
BMI, kg/m 30.69 30.56 30.64 30.97 30.56 30.66
Waist circum., cm 95.62 94.80 94.42 97.55 96.71 97.30
Hip circum., cm 113.90 113.66 113.26 113.56 113.65 112.28
Fat mass, kg 32.93 33.09 33.31 31.91 32.21 31.91
Fat-free mass, kg 51.99 51.66 51.66 50.71 50.26 49.68
Hunger, mm 43.64 39.10 43.87 42.61 43.48 39.59
Fullness, mm 34.34 48.18 38.86 40.00 45.65 50.00
Cholesterol, mg/dL 207.00 200.06 194.50 204.60 203.13 207.33
HDL, mg/dL 47.81 45.75 48.25 54.40 52.80 52.60
LDL, mg/dL 134.00 128.94 128.12 129.47 127.47 128.73
Triglycerides, mg/dL 125.31 126.00 115.94 104.13 114.40 130.33
Glucose, mg/dL 87.38 82.79 88.06 87.93 89.33 91.00

secondary outcomes. This is in contrast to several other fullness sensations between the two groups. To effectively
studies that have found beneficial effects of glucomannan on coordinate dosing and eating schedules, a more tailored or
body weight, body composition, and plasma lipid and glucose individualized approach should be considered.
levels [20, 26]. While the dosage (3.99 g/day) of glucomannan used in
Several factors may explain our study’s nonsignificant our study was similar to or at the lower range of those used
findings. Unlike previous studies, we enrolled only healthy in other studies, a higher dosage of glucomannan should be
overweight and moderately obese individuals consuming tested in future studies. Of special interest would be whether
self-selected diets and maintaining usual physical activity higher doses of glucomannan might be more effective in this
levels. As noted by Sood et al. [20], the beneficial effects of
population. Ten grams of soluble fiber per day is considered
glucomannan on weight loss may be enhanced by dietary
the maximum practical dose [27].
modifications, such as hypocaloric diets. Additionally, past
studies have focused on obese patients, so it is possible Three limitations of this trial should be considered. First,
that glucomannan may exert differential effects on these our final sample size (𝑛 = 47) was relatively modest. Given
individuals compared to the overweight or moderately obese the type II error that can occur with small sample sizes, this
(mean BMI = 31) participants in the present study. might be a possible explanation for lack of treatment effects.
The lack of body composition changes may be due to the Second, the moderate duration of our study did not permit
absence of an exercise intervention as part of the study design. either long-term safety or efficacy evaluation. Glucomannan
Other trials suggest that glucomannan in conjunction with was generally well tolerated and liver enzymes and serum
resistance and endurance exercise is necessary to promote creatinine levels remained favorable during the 8-week study
changes in body composition, including waist and hip cir- period; however, few studies have examined the long-term
cumference, fat mass, and fat-free mass [26]. safety of glucomannan, and this should be a focus of future
We also found no changes in plasma lipid or glucose trials since extended use may impact intestinal absorption of
concentrations. A possible explanation is that we enrolled key nutrients, particularly fat-soluble vitamins, carotenoids,
only healthy individuals and excluded those with dyslipi- and phytosterols. Similarly, glucomannan may be more ben-
demia or elevated serum glucose. Thus, floor effects may eficial over the long term when used with healthy overweight
have precluded detecting any effects of glucomannan on and moderately obese individuals. Third, we relied on self-
these parameters. Another possible explanation is the lack of report and capsule counts to monitor compliance. While
weight loss in our sample and its effects on these parameters participants in both groups reported a slightly greater than
[19]. 80% compliance rate, it is possible that physiologic measures
Irregular eating patterns also may provide an explanation of compliance such as end product metabolites of glucoman-
for our results. Rather than eating 3 meals, many partici- nan coupled with the use of electronic capsule monitoring
pants reported that they “grazed” throughout the day and systems would have resulted in more precise measures of
ate the majority of their calories in the evening, possibly compliance. In addition to phone and e-mail reminders, other
circumventing our dosing schedule of 2 capsules one hour technological measures to improve compliance such as text
before breakfast, lunch, and dinner. Similarly, irregular eating message reminders and tweets would be of interest in future
patterns may explain the lack of difference in hunger and studies.
6 Journal of Obesity

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Oxidative Medicine and
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Hindawi Publishing Corporation Hindawi Publishing Corporation Hindawi Publishing Corporation Hindawi Publishing Corporation Hindawi Publishing Corporation
http://www.hindawi.com Volume 2014 http://www.hindawi.com Volume 2014 http://www.hindawi.com Volume 2014 http://www.hindawi.com Volume 2014 http://www.hindawi.com Volume 2014