A Meta-Analysis on Randomised Controlled Clinical Trials Evaluating the Effect of the Dietary Supplement Chitosan on Weight Loss, Lipid Parameters and Blood Pressure

Background and objectives: Erratic results have been published concerning the influence of the dietary supplement chitosan used as a complementary remedy to decrease the body weight of overweight and obese people. The published articles mention as secondary possible benefits of usage of chitosan the improvement of blood pressure and serum lipids status. We performed a meta-analysis evaluating body weight, body mass index, total cholesterol, high density lipoprotein cholesterol, low density lipoprotein cholesterol, triglycerides, systolic and diastolic blood pressure among overweight and obese patients. Materials and Methods: Searching MEDLINE, Cochrane up to December 2017 on clinical trials that have assessed the influence of chitosan used as a dietary supplement on overweight and obese patients. An additional study was identified in the References section of another meta-analysis. A total of 14 randomised control trials (RCT) were used to assess the effect on body weight, serum lipids and blood pressure. Results: The usage of chitosan as a dietary supplement up to 52 weeks seems to slightly reduce the body weight (−1.01 kg, 95% CI: −1.67 to −0.34). Considering the other parameters studied, the most significant improvement was observed in systolic and diastolic blood pressure: −2.68 mm Hg (95% CI: −4.19 to −1.18) and −2.14 mm Hg (95% CI: −4.14 to −0.14) in favour of chitosan versus a placebo. Conclusions: Based on the meta-analysis realized with 14 RCT we concluded that the usage of chitosan as a dietary supplement can lead to a slight short- and medium-term effect on weight loss and to the improvement of serum lipid profile and cardiovascular factors.


Introduction
Overweight and obesity are predictors of health status being tightly correlated with alterations of blood pressure [1,2], blood lipids [3] and glucose homeostasis [4,5] as well as the presence of several cardiovascular diseases [6]. Overweight and obesity are defined by a body mass index (BMI) of 25-29.9 and ≥30 kg/m 2 , respectively [6] and are increasing rapidly in most of the European Union's (EU) population. It was estimated that in 2014, 51.6% of the adult (18+) population of the EU was overweight [7], while the prevalence of obesity in women was 6.2-36.5% and in men it ranged from Various clinical trials have been performed in the past 25 years investigating the effect of chitosan on body weight, body mass index (BMI), lipid parameters, blood pressure, glucose levels and other health characteristics [6,[29][30][31][32][33]. The last meta-analysis quantifying these studies (the Cochrane systematic review of Jull 2008) concluded that these effects were probably not of clinical significance [34]. Additional clinical trials have been conducted since 2008, some of them with a higher number of participants and a longer duration.
Therefore, the present meta-analysis aims at comprehensively summarizing and quantifying the effects of short-term and medium-term chitosan supplementation as a weight loss treatment, in individuals with a body mass index ≥23. 6  Various clinical trials have been performed in the past 25 years investigating the effect of chitosan on body weight, body mass index (BMI), lipid parameters, blood pressure, glucose levels and other health characteristics [6,[29][30][31][32][33]. The last meta-analysis quantifying these studies (the Cochrane systematic review of Jull 2008) concluded that these effects were probably not of clinical significance [34]. Additional clinical trials have been conducted since 2008, some of them with a higher number of participants and a longer duration.
Therefore, the present meta-analysis aims at comprehensively summarizing and quantifying the effects of short-term and medium-term chitosan supplementation as a weight loss treatment, in individuals with a body mass index ≥23.6, in RCTs.

Search Strategy
This study was designed according to the guidelines of the 2009 preferred reporting items for systematic reviews and meta-analysis (PRISMA) statement [35]. Medline (via Pubmed), EMBASE databases and the Cochrane Library were searched to identify randomised control trials (RCTs) examining the effects of chitosan supplementation on overweight and obese patients using the following search terms in titles and abstracts (also in combination with MESH terms): ("Chitosan") and ("randomized controlled trial" or "obesity" or "overweight"). Only articles available in English were included. The search was limited to studies on humans. We also reviewed bibliographies of original research and previous reviews to complement the search. The literature was searched from inception to 31 December 2017. We also searched trial registries of ongoing trials. Additionally, we contacted authors to obtain additional data.

Study Selection
Original studies were included if they met the following inclusion criteria: (1) RCT (≥28 days follow-up) performed in subjects over 18 years of age; (2) individuals with a body mass index ≥23.6; (3) compared chitosan with placebo, (4) investigated the impact of chitosan on body weight and/or BMI, (5) used random allocation to the comparison groups and (6) presentation of sufficient information on baseline and at the end of the study in both chitosan and control groups. Additional parameters like blood lipids: plasma total cholesterol (TC), high density lipoprotein cholesterol (HDL-C), low density lipoprotein cholesterol (LDL-C), and triglycerides (TG); systolic blood pressure (SBP) and diastolic blood pressure (DBP) were also included if available.
Exclusion criteria were: (1) non-clinical studies; (2) uncontrolled trials; (3) studies reported in abstract form or letters only and (4) lack of sufficient information on baseline or follow-up parameters. Exclusion of an article for the latter reason was applied if no feedback was received after contacting the author(s).

Data Extraction
Eligible studies were reviewed and from each study the following data were abstracted: first author's name; year of publication; study location; study design (crossover or parallel; single blind or double blind); intervention duration; form and dosage of chitosan intake; number of participants in the chitosan and control groups; age, gender and body mass index (BMI) of study participants; circulating concentrations of total cholesterol, LDL-C, HDL-C and triglycerides; systolic and diastolic blood pressure.
The data was extracted by two reviewers using a four-eye principle. The data included general trial characteristics, baseline parameters of individuals and outcome parameters (weight, BMI, cholesterol, triglycerides and blood pressure). Disagreement was resolved by consensus.

Quantitative Data Synthesis and Analysis
Meta-analysis techniques were used to combine the results from distal follow-up (the last follow-up reported) from independent studies [36]. Effect size was expressed as the weighted mean difference (WMD) and 95% confidence intervals (CI) between chitosan supplementation and placebo for continuous outcomes. Heterogeneity across the studies was tested using the I 2 index.
A random-effects model and the generic inverse variance method were used to compensate for the heterogeneity of studies in terms of study design, chitosan dose and demographic characteristics (e.g., age, gender, underlying disease and comorbidities) of populations studied.
All tests were two-tailed and a p-value of <0.05 was considered statistically significant in all analyses. The pooled estimates of the effect were calculated using Review Manager (RevMan) (Computer program, Version 5.3. Denmark, Copenhagen: The Nordic Cochrane Centre, The Cochrane Collaboration, 2014). Plasma lipids (TC, LDL-C, HDL-C and TG) concentrations were expressed in mmol/L. Dividing by 38.6 and 88.5 was used to convert cholesterol (TC, LDL-C, HDL-C) and TG, respectively, expressed in mg/dL into mmol/L.

Retrieved Data and Characteristics of the Trials
Twenty-six full text articles were assessed for eligibility, 12 studies were excluded for not assessing or not providing data about weight or BMI. Figure 2 shows the number of studies assessed and excluded through the stages of the meta-analysis. 38.6 and 88.5 was used to convert cholesterol (TC, LDL-C, HDL-C) and TG, respectively, expressed in mg/dL into mmol/L.

Retrieved Data and Characteristics of the Trials
Twenty-six full text articles were assessed for eligibility, 12 studies were excluded for not assessing or not providing data about weight or BMI. Figure 2 shows the number of studies assessed and excluded through the stages of the meta-analysis. A summary of the basic characteristics of the included trials and participants is given in Table 1. After final assessment, 14 RCTs fulfilled the inclusion criteria and were preferred for the final meta-analysis. A summary of the basic characteristics of the included trials and participants is given in Table 1. After final assessment, 14 RCTs fulfilled the inclusion criteria and were preferred for the final meta-analysis. Subjects were asked to follow a behavior modification plan and their physical activity was monitored. The treatment group took the following substances in addition: Beta-glucan, sno white oat fiber, betaine hydrochloride and aloe saponins (1 mg of each). Intake of at least 1.5 L of water per day.
Most studies included men as well as women (except for Schiller 2001 [38] and Bokura 2003 [26], women only). Ho 2001 [41] presented separate results for men and women. The age of the study participants was from 18-70 years. The criteria for overweight and obese varied from study to study. Chitosan dosage ranged from 0.34 g/day-3.4 g/day (mean 2 g/day) and one study [40] did not report any dose. Preparations containing other active substances were used in five studies [29,33,[38][39][40] while other studies used only chitosan. Table 1 presents these characteristics.
The efficacy of chitosan at various doses coupled with calorie restriction was investigated [30] Other studies advised their patients not to modify their habitual diet or lifestyle [23,26,29,[31][32][33]38,40]. Two studies [23,41] did not report significant body weight reduction in the chitosan group compared to the placebo group, while the others found that chitosan led to significant weight loss.

Types of Outcome Measures
The studies included in this meta-analysis did not perform any extended follow-up beyond the intervention period, i.e., the outcomes were measured post-intervention only.
Most studies included men as well as women (except for Schiller 2001 [38] and Bokura 2003 [26], women only). Ho 2001 [41] presented separate results for men and women. The age of the study participants was from 18-70 years. The criteria for overweight and obese varied from study to study. Chitosan dosage ranged from 0.34 g/day-3.4 g/day (mean 2 g/day) and one study [40] did not report any dose. Preparations containing other active substances were used in five studies [29,33,[38][39][40] while other studies used only chitosan. Table 1 presents these characteristics.
The efficacy of chitosan at various doses coupled with calorie restriction was investigated [30] Other studies advised their patients not to modify their habitual diet or lifestyle [23,26,29,[31][32][33]38,40]. Two studies [23,41] did not report significant body weight reduction in the chitosan group compared to the placebo group, while the others found that chitosan led to significant weight loss.

Types of Outcome Measures
The studies included in this meta-analysis did not perform any extended follow-up beyond the intervention period, i.e., the outcomes were measured post-intervention only.

Discussion
Chitosan has been studied as an agent for lowering weight, cholesterol and blood pressure since it is not well digested in the human body. Chitosan appears to bond with fatty compounds in the digestive tract, carrying them out in the faeces [34].
Chitosan and its derivatives have been widely promoted and are freely available in health stores and pharmacies [24]. In 2015 the global market for chitosan valued 3.19 billion USD, Japan covering 35% of chitosan production [43].
A number of human trials have reached different conclusions concerning the effect of chitosan on weight loss. Although early studies conducted with hypocaloric diets suggested that chitosan had a significant effect on body weight [44][45][46], later clinical trials showed a much smaller effect [38], or no effect at all when compared to a placebo [23,37]. The meta-analysis of Ernst [47] suggested a 3.3 kg greater weight loss with chitosan compared with placebo, while two more recent meta-analyses [34,48] suggested only a 1.7 kg weight loss.
Since then, the efficacy of chitosan was investigated at different doses and also when administered concomitantly with a calorie-restricted diet and physical activity in various short-term and medium-term studies.
This meta-analysis provides an overview on the efficacy of chitosan as a treatment for overweight and obesity. The authors compared the effect of chitosan and placebo for overweight and obese patients on factors such as weight, BMI and other parameters related to metabolic disease. The

Discussion
Chitosan has been studied as an agent for lowering weight, cholesterol and blood pressure since it is not well digested in the human body. Chitosan appears to bond with fatty compounds in the digestive tract, carrying them out in the faeces [34].
Chitosan and its derivatives have been widely promoted and are freely available in health stores and pharmacies [24]. In 2015 the global market for chitosan valued 3.19 billion USD, Japan covering 35% of chitosan production [43].
A number of human trials have reached different conclusions concerning the effect of chitosan on weight loss. Although early studies conducted with hypocaloric diets suggested that chitosan had a significant effect on body weight [44][45][46], later clinical trials showed a much smaller effect [38], or no effect at all when compared to a placebo [23,37]. The meta-analysis of Ernst [47] suggested a 3.3 kg greater weight loss with chitosan compared with placebo, while two more recent meta-analyses [34,48] suggested only a 1.7 kg weight loss.
Since then, the efficacy of chitosan was investigated at different doses and also when administered concomitantly with a calorie-restricted diet and physical activity in various short-term and medium-term studies.
This meta-analysis provides an overview on the efficacy of chitosan as a treatment for overweight and obesity. The authors compared the effect of chitosan and placebo for overweight and obese patients on factors such as weight, BMI and other parameters related to metabolic disease. The

Discussion
Chitosan has been studied as an agent for lowering weight, cholesterol and blood pressure since it is not well digested in the human body. Chitosan appears to bond with fatty compounds in the digestive tract, carrying them out in the faeces [34].
Chitosan and its derivatives have been widely promoted and are freely available in health stores and pharmacies [24]. In 2015 the global market for chitosan valued 3.19 billion USD, Japan covering 35% of chitosan production [43].
A number of human trials have reached different conclusions concerning the effect of chitosan on weight loss. Although early studies conducted with hypocaloric diets suggested that chitosan had a significant effect on body weight [44][45][46], later clinical trials showed a much smaller effect [38], or no effect at all when compared to a placebo [23,37]. The meta-analysis of Ernst [47] suggested a 3.3 kg greater weight loss with chitosan compared with placebo, while two more recent meta-analyses [34,48] suggested only a 1.7 kg weight loss.
Since then, the efficacy of chitosan was investigated at different doses and also when administered concomitantly with a calorie-restricted diet and physical activity in various short-term and medium-term studies.
This meta-analysis provides an overview on the efficacy of chitosan as a treatment for overweight and obesity. The authors compared the effect of chitosan and placebo for overweight and obese patients on factors such as weight, BMI and other parameters related to metabolic disease. The overall finding of this meta-analysis is that chitosan may be effective as an adjuvant treatment in weight loss programs.
In the studies analysed in this meta-analysis, the daily intake of chitosan varied from 0.34-3.4 g/day. One study did not mention the amount of chitosan administered to the patients [40].

Comparison with Other Meta-Analysis
Our results are supported by two systematic reviews that showed some weight loss and further improvements in cardiovascular risk factors after chitosan supplementation compared with a placebo treatment [34,48]. Both meta-analyses showed a mean weight loss of 1.7 kg.
The systematic review of Ni Mhurchu [48] included 14 randomised placebo-controlled clinical trials with a total of 1131 participants assessing chitosan as a weight reduction agent. The duration of the studies ranged from 4-24 weeks. The results showed a slight reduction of weight compared with the placebo.
The meta-analysis of Jull [34] that compared and reviewed 15 randomised controlled trials, reported evidence that chitosan was more effective than a placebo in the treatment of overweight and obesity, high blood pressure and slightly effective for lowering total cholesterol and triglycerides. The study included 1219 patients with treatment duration of 4-24 weeks.
Both previous systematic reviews mentioned that the results of several of the included trials should be interpreted with caution due to their poor quality and unsuccessful correspondence with their authors [34,48]. Overall results from high quality trials only demonstrated minimal effect from chitosan on body weight.
The present meta-analysis reports that chitosan oral supplementation led to greater body weight loss than placebo treatment for obesity for up to 52 weeks of follow-up. The mean weight difference of −1.01 kg achieved over trial periods ranging from 4-52 weeks was minor. However, our analysis showed a significantly greater decrease in intervention group in comparison with the placebo for TC, LDL cholesterol, and TG. Furthermore, HDL cholesterol increased after chitosan supplementation. Decreasing TC, LDL, TG and increasing HDL represents an important clinical target [49]. The effect of chitosan on total cholesterol levels was similarly reduced (−1.39 mmol/L (95% CI, −2.17 to −0.62)) but remained statistically significant (P < 0.0004) although its clinical significance is also questionable.
In our meta-analysis on overweight and obese patients the chitosan supplementation was associated with a significant decrease in SBP and DBP with −2.68 mm Hg (95% CI −4.19 to −1.18) and −2.14 mm Hg (−4.14 to −0.14) in favour of chitosan versus placebo. The Heart Outcome Prevention study showed that a decrease in SBP of 2-3 mm Hg in patients with diabetes and one other risk of cardiovascular morbidity was associated with a 25% reduction in risk of myocardial infarction, or cardiovascular death [50]. Table 2 presents a comparison between the meta-analysis of Jull 2008 [34] and our meta-analysis. The systematic study of Jull [34] showed a slight improvement in cardiovascular risk factors, while our meta-analysis showed more improvement on cholesterol, TG and BMI.
The most common adverse events after chitosan treatment in analysed studies were constipation and diarrhoea. Table 2. Comparison between the results obtained in our meta-analysis and a previous meta-analysis.

Strengths and Limitations of Study
The interpretation of these meta-analysis results should take into account that several studies also used other active substances in addition to chitosan, were of limited size or duration (are 3 months or less) or did not include parameters like blood pressure, cholesterol, and triglycerides. In addition, some potentially informative trials were not included if the participants' weight or BMI was not assessed [51][52][53].
Our study did not include five clinical trials published in 1995-1996 [44][45][46]54,55] since correspondence with their authors was unsuccessful. Concerns were expressed about a systematic bias in these studies since the chitosan was supplied by one manufacturer and the studies appeared in the same Italian journal [34,47]. A meta-analysis study based on these trials reported a significant effect of chitosan as a weight loss supplement (−3.3 kg) [47], however later studies reported that the difference in terms of weight loss between control and chitosan was considerably smaller (−1.7 kg) [34,48].

Conclusions
This meta-analysis of data from 14 RCT provided comprehensive evidence that compared with the placebo, chitosan supplementation leads to a slight short-and medium-term effect on weight loss of chitosan supplementation, improves plasma lipid profile and cardiovascular outcomes. In summary, this meta-analysis establishes a beneficial effectiveness on overweight and obese patients. Considering the impact of the aforementioned factors on the overall health state of the patients, we may conclude that chitosan intervention improves the overall prognosis of these people. However, additional long-term research is needed, stating all of the characteristics of the chitosan formulations.