Chitosan - For Weight Loss and Cholesterol Control

Fiber and its use as a weight loss aid and cholesterol lowering agent has been the topic of considerable study in the last several decades. Research has shown that increasing fiber intake usually leads to decreased serum cholesterol levels and, more importantly, increased ratios of high density (HDL-cholesterol) to low density (LDL -cholesterol) lipoproteins which is well documented to be protective against cardiovascular disease.

Increasing dietary fiber intake quite often decreases fat intake, as fiber-rich foods are relatively low in fat and cholesterol.

The mechanisms behind these fat- and cholesterol-lowering effects are due to the fact that fiber can reduce gastrointestinal transit time, as well as inhibit lipid absorption and bile acid reabsorption. Increased fiber intake leads to increased fecal excretion of bile acid components (which includes cholesterol) and fats.

Fiber, in general, has been shown to be a promising tool for weight loss and control of cholesterol levels. Specific types of fibers, however, act in different ways. Most of the studies conducted have focused on plant fibers: brans, gums, and pectin, but these are not the only fibers available. One novel type of fiber that has recently gained popularity as a weight loss and cholesterol-lowering aid is chitosan.

Chitosan is made by deacetylation of chitin, the cellulose-like material found in the outer shells (exoskeletons) of insects, crabs, lobster, etc., and in fungal cell walls. Unlike most plant fibers, chitosan has positively charged amino groups which form ionic bonds with lipids and bile components. While negatively charged (plant -based) fibers simply act passively as a barrier to inhibit absorption of lipid and bile, positively charged fibers prevent absorption by (ionic) binding to the (negatively charged) lipids. Chitosan is also unique among fibers in that it is the only natural fiber soluble at gastric pH levels.

The mechanism of how chitosan affects lipid and cholesterol levels awaits elucidation, but it is most likely mediated by its actions on micelle (lipid transporter) formation in the gut. Mixed micelles in the gastrointestinal tract contain free fatty acids, cholesterol, and various other components, and are the method by which lipids are absorbed into the blood stream. Chitosan is thought to act by binding to the free fatty acids and bile acid components, removing them from the micelles and thus disrupting lipid absorption.

Effects on Blood Lipid Profiles

Numerous studies have examined the cholesterol-lowering and fat-lowering effects of chitosan. Most of these studies, with few exceptions, have been conducted in laboratory animals, but their results are still encouraging for humans.

In 1978, a group of researchers fed adult male rats high cholesterol diets containing either chitosan, cellulose (the best known plant fiber), or cholestyramine (a synthetic resin that binds to cholesterol in the gut). Results showed that cholesterol-fed rats given chitosan had lower plasma cholesterol levels than rats receiving either the cellulose or the cholestyramine. Subsequent studies by this same group have yielded similar results. Rats fed high cholesterol diets containing 2 to 5% chitosan showed marked reductions (25-30%) in plasma cholesterol levels; and when animals were fed a cholesterol-free diet containing only 0.5% chitosan for several months, serum cholesterol levels were unchanged, but the ratio of high density (good) to low density (bad) lipoproteins was significantly increased.

Studies on the effect of chitosan on intestinal absorption in adult rats have shown that chitosan treatment results in significant decreases in the absorption of cholesterol and other lipids (47-51% and 32-41% respectively) levels that are similar to that achievable by treatment with cholestyramine. Not surprisingly, chitosan treatment evoked no side effects (as compared to diarrhea and constipation, seen with cholestyramine treatment).

One means by which chitosan is thought to affect lipid and cholesterol levels is by altering the metabolism of bile in the gut. This has been unequivocally documented in animal studies, and results of recent clinical trials appear to confirm this phenomenon in humans. While the total amount of bile acids which are excreted does not change, the composition of those which are excreted does: chitosan treatment results in increased excretion of lipid components.

Effects on Weight Loss

Given chitosan's properties as a fiber, and particularly it's ability to decrease the absorption of lipids, it is surprising that more research has not been carried out on weight loss. Nevertheless, several chitosan products are now on the market, and anecdotal evidence indicates the satisfaction of many users. One private company has done an in-house, double blind, placebo controlled study with reportedly impressive results. Given the ability of chitosan to absorb up to 12 times its weight of lipids, further study in humans to develop an optimal dosage is obviously necessary and desirable.