BACKGROUND: The use of dietary supplements, especially those for weight control, is increasing. Advertising claims for some of these supplements may give consumers unrealistic expectations. For example, it is claimed that the supplement chitosan can block the absorption of up to 120 g of dietary fat per day.
OBJECTIVE: To test the effect of a chitosan supplement used as directed, on the absorption of dietary fat.
DESIGN: Seven healthy male volunteers with average age 28, range 23–30, average body mass index (BMI) 26, range 23–31, maintained a high fat intake (>120 g/day) for 12 days. On days 6–9, chitosan was taken as directed by the manufacturer prior to meals and snacks and totaled 15 capsules or 5.25 g of chitosan daily. A charcoal marker was consumed on days 2, 6 and 10 to mark the baseline and supplement periods. All feces were collected on days 2–12, and were divided based on the appearance of charcoal in the feces. Fecal fat content corresponding to the four baseline and four chitosan-supplemented days was measured.
RESULTS: Average dietary fat intake did not differ between baseline (135±5 g), and chitosan (135±3 g) periods. Fecal fat excretion did not differ between the two periods (6.9±1.0 g/day baseline; 6.8±0.4 g/day chitosan). The fecal fat content as a percentage of fat consumed did not differ (5.1±0.7% baseline, 5.0±0.3% chitosan). Fecal mass did not differ (176±26 g/day baseline, 182±14 g/day chitosan).
CONCLUSION: Consumption of this chitosan supplement did not increase fecal fat content and therefore did not block fat absorption.
More than 40% of Americans consume one or more dietary supplements in the belief that doing so will enhance their health.1 However, health claims associated with supplements are often unsubstantiated. This is particularly true in the case of supplements marketed for weight loss, such as chitosan. The sales in the USA of the top three brands of chitosan exceeded $6 million between February 1999 and February 2000, despite the lack of clinical evidence for their efficacy.2
Chitosan is the N-deacetylated derivative of the polysaccharide chitin found in the shells of invertebrates such as shrimp and crabs.3 Chitosan supplements are marketed as ‘fat blockers’ or ‘fat trappers’. It is claimed that chitosan blocks the absorption of as much as 120 g of dietary fat per day, and that this will promote weight loss.4 Given that dietary fat not absorbed must be excreted in the feces, the claim for chitosan can be tested in humans by measuring its effect on fecal fat excretion. This study was designed to test whether chitosan blocks fat absorption. We analyzed the fat content of feces from seven healthy male subjects consuming over 120 g of fat per day, comparing a 4 day baseline period to a 4 day chitosan-supplemented period.
Subjects and methods
Announcements calling for male volunteers between the ages of 21 and 40 y were posted at the University of California, Davis medical school campus. Each prospective subject was interviewed by one of the investigators and a registered dietitian. The design of the study was explained to them and they were asked to recall all foods and portions eaten in the previous 24 h. After 11 subjects were interviewed, seven were chosen based on subjective evaluation of their dietary recall performance, a high food intake (>10 MJ/day), and understanding of the study. The seven active males selected for participation averaged 28 y of age, with a range of 23–30, and had an average body mass index (BMI) of 26, with range 23–31. The research protocol was approved by the Human Subjects Review Committee at the University of California, Davis.
The energy requirement for weight maintenance was estimated for each subject using information supplied by the Shape Up America's website.5 This calculation was based on the Mifflin equation for resting energy expenditure (REE)6 and multiplication by an activity factor. The activity factors for men were 1.3 (sedentary-light), 1.5 (moderate), 1.7 (heavy) and 1.9 (very heavy) based on slight modification of recommendations given by the Food and Nutrition Board of the Institute of Medicine, National Academy of Sciences.7 Each subject chose foods from a list of 70 prepared packaged or frozen foods with the assistance of one of the investigators to meet total energy requirement for weight maintenance and to contain over 120 g of fat per day. Food was directly supplied to the subjects. Food consumption was divided into three meals and three snacks per day. The prescribed foods represented a mandatory minimum intake for each subject. After each subject consumed the prescribed foods at each meal/snack, he was allowed to eat additional food items. Subjects were informed that a high fat intake was critical for the study. Thus, in the unexpected event that substitutions needed to be made, foods high in fat were to be selected. The type and quantity of all foods eaten were recorded every day in a journal, including the time of day and amount eaten. To calculate daily intakes of nutrients, nutritional information was taken from food labels for packaged foods and from a standard reference for items without a corresponding food label.8
Subjects consumed 100 ml of a 10% charcoal solution orally prior to breakfast on days 2, 6 and 10 (Actidose-Aqua, Paddock Labs, Minneapolis, MN, USA). This charcoal served as a marker, giving the feces a distinctively black color and permitting the association of a particular meal with a particular fecal sample. Each subject collected all feces passed from day 2 to day 12 using commode specimen collection systems (CMS/Fischer Healthcare, Houston, TX, USA). The time and date of each sample, as well as the presence of the charcoal maker in a given sample, were recorded by the subjects on the sample label and in their daily journals. A fecal sample was considered to contain charcoal when at least half of the sample was visibly colored with charcoal. The final determination for each sample was made by the investigator after all samples were submitted. The pool of fecal samples that constituted the baseline period included the feces containing the first charcoal marker (taken on day 2) and ended just prior to the appearance of the second marker (taken on day 6). The pool of fecal samples that constituted the supplement period included the feces containing the second marker and ended just prior to the appearance of the third marker (taken on day 10). The 14 resulting pools of fecal samples (seven subjects×two periods) were individually analyzed for fat content by the National Institutes of Health-funded UC Davis Clinical Nutrition Research Unit Assessment Laboratory using the gravimetric modification of the Van de Kamer method.9
Each capsule of the supplement contained 0.35 g chitosan and 0.05 g psyllium husks (Chytozyme™, Enforma Fat Trapper Plus, Enforma Natural Products Inc., Pacoima, CA, USA). The chitosan used in the formulation was LipoSanUltra™ (Vanson, Washington, USA). The level of deacetylation in LipoSanUltraTM was not less than 78%. To determine the dose of chitosan used, we first considered the recommendations associated with this supplement. Instructions on the product label suggest that three to five capsules be taken with each high fat meal (1.05–1.75 g chitosan/meal). However, a 2 month supply consists of 240 capsules,10 leading to the conclusion that the recommended dose is four capsules daily, equivalent to 1.4 g chitosan/day. We then looked at published studies in humans, where a significant drop in blood cholesterol was observed with chitosan use at effective doses ranging from 1.35 to 3.0 g daily.11,12 This suggested to us that an effective dose, if one existed, might be at the high end of the intake suggested by the manufacturer and the distributor. Therefore, we instructed subjects to take a total of 15 capsules daily (5.25 g chitosan/day). On days 6–9, capsules containing chitosan were taken prior to each of three meals (three per meal) and each of three snacks (two per snack). Capsules were consumed with water 5 min before food was consumed, as indicated in the manufacturer's directions on the product label. To facilitate compliance, each subject was given a pre-filled pill container; each compartment was identified with four dates for three meals and three snacks per day. Subjects were blinded to the content of the capsules. Subjects were instructed not to take any vitamins or any other dietary supplements during the course of the 12 day study.
Data were evaluated using Student's paired t-test to compare the baseline and treatment periods. To compare body weights at three time points, repeated measures one-way ANOVA was used. A P-value of <0.05 was considered statistically significant. Statistical analyses were performed with Graphpad Prism (Graphpad Software Inc., San Diego, CA, USA). Values are expressed as means±standard errors.
The dietary intake for baseline and supplement periods did not differ with respect to total energy, total fat, saturated fat, cholesterol, dietary fiber (excluding the supplement which contributed 6.0 g of dietary fiber per day), sugars, or protein (Table 1). The average carbohydrate consumption during the supplement period (359±25 g/day) was 8% higher than during the control period (333±18 g/day; P<0.05).
Fecal fat excretion did not differ, averaging 6.9±1.0 and 6.8±0.4 g/day, for baseline and supplement period, respectively, P=0.81 (Figure 1). Fecal fat output, expressed as percentage of fat intake, did not differ, 5.1±0.7% for baseline and 5.0±0.3% for the supplement period, P=0.87 (Figure 1). Figure 1 illustrates these comparisons and includes dietary fat intake. Fecal mass did not differ between the two periods (176±26 g/day baseline, 182±14 g/day supplement, P=0.78). Body weights did not change during the supplement period (80.8±3.2 kg at day 6 vs 81.0±3.2 kg at day 12) but there was a significant decrease during the control period of 1.0±0.4 kg from the initial weight of 81.7±3.2 kg. No subjects reported diarrhea, constipation, or any other adverse effects. However, three subjects reported light abdominal upset immediately following consumption of the charcoal solution. Considering all fecal collections, the elapsed time between consumption of the charcoal and its appearance in the feces was 26.8±3.0 h.
Chitosan is a derivative of the polysaccharide chitin found in the shells of invertebrates such as shrimp and crabs.3 Chitin is a (1–4)-linked 2-acetamido-2-deoxy-β-glucan; chitosan is the N-deacetylated derivative.3 Enzymes to digest chitosan are not produced by the digestive tracts of animals, but intestinal microflora secrete chitinase and chitosanase.3 Chitosan has been shown in vitro to bind and precipitate 4–5 times its weight in micellar lipids including bile salts, cholesterol, and triglyceride.13 Chitosan is proposed to bind bile acids with ionic bonds in the same manner as cholestyramine.14,15 The deacetylation of chitin to form chitosan increases the positive charge density on the molecule, permitting it to form these bonds.14 Studies in rats,16,17 and in humans11,12 suggest that dietary chitosan increases bile acid excretion and decreases plasma cholesterol.
In a review of the literature, only one abstract was found that reported chitosan's effects on fecal fat excretion in humans. Excretion averaged 4.5±3.4% of fat intake and the authors concluded that chitosan had no effect on fat absorption.18 The only direct evidence for physiologically significant malabsorption of fat due to chitosan consumption comes from work with experimental animals. The apparent fat digestibility of a defined diet containing a high dose of chitosan (5% w/w) and 20% (w/w) corn oil fed to rats was 51±22% compared to 95±2% using a cellulose-containing control diet.19 In another study, the use of a high viscosity chitosan at 5% w/w of diet with rats also reduced the apparent fat digestibility to about 50%.19 For our subjects eating 12 MJ/day, chitosan at 5% w/w equates to approximately 28 g of chitosan per day. This would require the consumption of 80 capsules of this supplement taken daily. Based on the aforementioned studies in rats, even if our subjects consumed 28 g of chitosan daily, only 50% or less than 70 g of the 135 g of dietary fat eaten would be excreted. It should be noted that, for the rats, the chitosan was integrated into the diet, thus maximizing contact between chitosan and dietary fat prior to consumption. When capsules are taken prior to the meal, as suggested by the manufacturer, mixing of chitosan with dietary fat will be less thorough and is therefore likely to be less effective.
In a meta-analysis of the literature on dietary chitosan use for weight-reduction in humans, five randomized double-blind studies were examined.20 The meta-analysis revealed that the average increment in weight loss in the chitosan-treated groups over placebo was 3.28 kg over a 4 week period. On an energetic basis, if this weight loss were attributed to fecal fat loss alone, excretion of more than 100 g dietary fat/day would be required. Because the studies used chitosan in conjunction with a reduced energy diet (4.18–5.02 MJ/day) containing only about 34% of energy from fat,21,22 we calculated that subjects were eating only 38–45 g of fat per day. Therefore, if chitosan contributed to weight loss, one must conclude that it acted through mechanism(s) other than lipid malabsorption. In two more recent studies, chitosan was used at 2 g/day for 4 weeks or 2.4 g/day for 8 weeks without dietary energy reduction and no effects on body weight were observed.21,22
In advertising materials for chitosan, it is claimed that it can prevent the absorption dietary fat, up to 120 g per day with this particular product, and can thus be used as a weight control aid for individuals maintaining a high fat diet.4 There are three lines of evidence that contradict this claim. The first line of evidence comes from the fact that even if one could extrapolate data from chitosan use in rats to that in humans, the dosage to achieve approximately a 50% reduction in fat digestibility, or an excretion of less than 70 g of fat per day for our subjects, would be an order of magnitude higher than that suggested by the manufacturer. The second line of evidence comes from two recent trials where chitosan use without energy restriction for 4 or 8 weeks failed to increase weight loss over placebo.21,22 The final, and most conclusive, line of evidence comes from the data reported here: chitosan did not increase fecal fat excretion and thus failed to act via its proposed mechanism. We did not test multiple chitosan products, but we do conclude that the central claim associated with this particular chitosan supplement, fat malabsorption, is false and the associated claims for weight loss are therefore misleading.
The present study illustrates the value and importance of clinical research in evaluating the efficacy of dietary supplements.
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This study was supported, in part, by a grant from the District Attorney's Office of Napa County and the UC Davis Clinical Nutrition Research Unit, NIH DK35747 Nutritional Assessment Laboratory. We thank Connie Belk, RD, for her assistance and Charles H Halsted, MD, for his help with the design of the study.
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Gades, M., Stern, J. Chitosan supplementation does not affect fat absorption in healthy males fed a high-fat diet, a pilot study. Int J Obes 26, 119–122 (2002). https://doi.org/10.1038/sj.ijo.0801859
- dietary fat
- dietary fiber
- adult males
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