The food and nutritional industries tend to "deconstruct" foods. With the aid of science, healthy constituents are found and extracted and/or purified, and then promoted as supplements for food fortification. Or, they are altered and used in pharmaceutical preparations. This is the case with vitamins and minerals and with many phytotherapeutic chemicals provided by herbs and spices.
This has extended to renewed interest in the "skeleton" structures that make up foods "the dietary fibers” as they are promoted for their various health benefits. For example, weight loss is an area for which fiber has both confirmed and purported benefits.
Weighing in on Weight Loss
Fiber is well-known to possess many health advantages, such as reducing the risk of heart disease by lowering LDL and total cholesterol levels, preventing constipation (insoluble fiber), and reducing the risk of colon cancer. Fibers also may benefit weight loss in that they increase the feeling of fullness (satiety) after meals, and also slow sugar absorption from the gut (as "brush-barriers"), balancing blood sugar levels and insulin levels. Certain fibers in pharmaceuticals, supplements, and now foods, are gaining attention for their claimed ability to block fat absorption. Basel, Switzerland-based F. Hoffmann-La Roche's orlistat (Xenicalâ„¢) is the most well-known of the pharmaceutically produced fibers, with substantial clinical evidence to prove its efficacy.
Chitosan is a dietary supplement "fat-blocking" fiber, with some clinical support. One company had promoted its chitosan-based ingredient as having obtained "self-affirmed GRAS" under FDA regulations, but pulled its self-affirmation notice earlier this year.
Other natural sources of fibers also are beginning to be advertised to consumers as fat-blockers. These new fat-blocking supplements are being formulated with dietary fibers that are theorized to have the same activity and/or fiber characteristics of the chitosan molecule that can absorb and block fat. Likely food sources for these fibers include guar gum, psyllium hulls, sesame seeds, and other gel-forming fibers. There is little scientific evidence that these fibers work by blocking fat; however, they may be beneficial for their other healthful characteristics, including their use in weight management to increase satiety and balance blood sugar (by slowing sugar absorption).
Chitosan at Work
Chitosan is a dietary fiber derived from chitin that is made as a byproduct of shellfish processing. Chitosan is formed as a product of the alkaline deacetylation of chitin (aminopolysaccharide, or a combination of a sugar and a protein). Chitosan not only exhibits biological activities (hypo-cholesterolemic, antimicrobial, wound healing) but also is being researched for its application in pharmaceutical drug delivery, as an excipient, binder, and tablet coater.
Chitosan is a positively-charged large fiber molecule that has the ability to attract and bind to fatty acids (which carry a negative charge). After forming "films" with the fats in the digestive system, it is not specifically hydrolyzed and, therefore, may bind the fats and pass them through the body undigested. Specifically, it is the positively charged tertiary amino group (-NH3+) of chitosan that attracts the anionic carboxyl groups of fatty acids and bile acids. Chitosan also interferes with the metabolism process of cholesterol (and other neutral lipids) by binding them with hydrophobic bonds.1
Clinical research on chitosan's role in weight loss has found mixed results. One recent study refuted chitosan's weight-reduction ability in people without controlled diets. However, chitosan does appear to reduce total serum cholesterol by 5.8-42.6% and LDL by 15.1-35.1%.1 Critics of the research claim that either chitosan needs to be used with a calorie-restricted diet and, therefore, many refuting studies are not properly designed, or that many of the studies were done with dosages that were too low.
On the Web: CHITOSAN & FIBER
- www.supplementwatch.com/supatoz/supplement.asp?supplementId=77 SupplementWatch.com's review of chitosan
- www.xenical.com Hoffman-LaRoche's website
- www.cfsan.fda.gov/~rdb/opa-g073.html FDA response to withdrawal of chitosan GRAS notification
- www.eatright.org/adap1097.html The ADA's position on fiber health benefits
- www.drumlib.com/dp/000023.htm Personal editorial on chitosan vs Xenical
- www.md-phc.com/fiber/indexfib.html Collection of article abstracts and short overview on dietary fibers and their health implications
- www.acsh.org/publications/priorities/0901/brannew.html American Council on Science and Health
- www.healthwell.com/healthnotes/Herb/Psyllium.cfm Healthwell overview article on psyllium
- www.dipasa.nl/propspag.htm Fiber and other nutritional content of fiber
One earlier Italian clinical study prescribed a combination of chitosan supplements and a low-calorie diet (1,000 cals/day). The results of this study were favorable, and supported the idea that chitosan should be used in combination with other dietary modifications. After 30 days of supplementation, the chitosan group produced a 16-lb. weight loss, whereas the placebo group only found a 7-lb. difference. In animal studies, chitosan has been reported to prevent an increase of body weight, hyperlipidaemia and fatty liver induced by a high fat diet.2
More recent studies on chitosan's effectiveness have been negative. A pilot study performed at UC Davis concluded that chitosan supplementation (at the rate of 5.25g daily) during a high fat diet did not increase fecal fat content and, therefore, block fat absorption.3 Another study funded by Hoffmann-La Roche compared the absorption ability of chitosan versus orlistat. Healthy volunteers were given either 120mg of orlistat three times daily or 890mg of chitosan three times daily for seven days, and then the groups were crossed-over. The fecal fat was analyzed in each group, and orlistat was found to significantly absorb fat (measured by increased fat in the feces), whereas chitosan was found to have no effect.4 Other studies found that chitosan supplementation was not effective in subjects without dietary alterations.5,6
Research that supports chitosan's fat-blocking ability indicates that 1g of chitosan blocks absorption of some 3-6 grams of fat. In experiments by Kanauchi et al., vitamin C appears to have an important synergy with chitosan.7 When mixed in the ratio of 3:1 (chitosan to ascorbate), the combination was found to a) reduce the viscosity of chitosan in the stomach, b) increase the capacity of chitosan to bind with more fat, and c) create a more flexible chitosan-fat gel that is less likely to break or leak in the intestinal tract. Many supplements on the market, however, combine chitosan with vitamin C at a ratio of 10:1.
Chitosan, considered to have a low toxicity, has been well-tolerated in the few short-term clinical studies, producing only mild and transitory nausea and constipation in 2.6-5.4% of subjects. Some research has shown that vitamin and mineral levels remain within normal parameters with chitosan supplementation; however, other studies have shown the fiber to decrease serum vitamin E levels, and decrease bone mineral absorption and content, requiring twice the amount of calcium supplementation in rats.8 Thus, vitamin supplementation has been recommended while using chitosan. Lastly, people allergic to crustaceans (shellfish) should avoid chitosan.1
As consumers continue to be intrigued with healthful products, it will be interesting to see the roles played by chitosan and other dietary fibers.
1 Ylitalo, R., et al. 2002. Cholesterol-lowering properties and safety of chitosan. Arzneimittelforschung 52(1):1-7.
2 Han, L.K., et al. 1999. Reduction in fat storage during chitin-chitosan treatment in mice fed a high-fat diet. Int J Obes Relat Metab Disord 23(2):174-9.
3 Gades, M.D. and J.S. Stern. 2002. Chitosan supplementation does not affect fat absorption in healthy males fed a high-fat diet, a pilot study. Int J Obes Relat Metab Disord 26(1):119-22.
4 Guerciolini R., et al. 2001. Comparative evaluation of fecal fat excretion induced by orlistat and chitosan. Obes Res 9(6):364-7.
5 Pittler M.H., et al. 1999. Randomized, double-blind trial of chitosan for body weight reduction. Eur J Clin Nutr, 53(5): 379-81.
6 Ho, S.C., et. al. 2001. In the absence of dietary surveillance, chitosan does not reduce plasma lipids or obesity in hypercholesterolaemic obese Asian subjects. Singapore Med J 42(1):006-10.
7 Kanauchi O., et. al. 1995. Mechanism for the inhibition of fat digestion by chitosan and for the synergistic effect of ascorbate. Biosci Biotechnol Biochem 59(5):786-90.
8 Deuchi K, et. al. 1995. Continuous and massive intake of chitosan affects mineral and fat- soluble vitamin status in rats fed on a high-fat diet. Biosci Biotechnol Biochem 59(7):1211-6.