Phytosterols (PS) or plant sterols are structurally similar to cholesterol. The most common PS are ␤-sitosterol, campesterol and stigmasterol. Epidemiologic and experimental studies suggest that dietary PS may offer protection from the most common cancers in Western societies, such as colon, breast and prostate cancer. This review summarizes the findings of these studies and the possible mechanisms by which PS offer this protection. These include the effect of PS on membrane structure and function of tumor and host tissue, signal transduction pathways that regulate tumor growth and apoptosis, immune function of the host and cholesterol metabolism by the host. In addition, suggestions for future studies to fill the gaps in our knowledge have been given. J. Nutr. 130: 2127-2130, 2000. Phytosterols (plant sterols, PS)4 are the counterparts of cholesterol in animal products. They have a structure similar to that of cholesterol but with some modifications. These modifications involve the side chain and include the addition of a double bond and/or methyl or ethyl group. The most common dietary PS are ␤-sitosterol (SIT), campesterol and stigmasterol (Fig. 1). The Western diet contains 80 mg PS/d, whereas vegetarian and Japanese diets contain 345 and 400 mg/d, respectively (1). The best dietary sources of PS are unrefined plant oils, seeds, nuts and legumes (2,3). Processing of plant oils (such as refining and deodorization) reduces PS content, but the loss varies with the type of oil (3). Hydrogenation of refined oils, however, has little effect on PS content (3).The interest in studying PS was due initially to their effectiveness in reducing the absorption of dietary cholesterol and thus offering protection from cardiovascular diseases (4,5).Several review articles on this subject have appeared in the literature (6,7) and thus will not be addressed here.Anticancer Properties of Phytosterols. In recent years, a great deal of interest has been given to the role of PS in the protection from cancer. Raicht et al. (8) suggested that dietary SIT may offer protection from chemically induced colon cancer. These authors examined the growth of methylnitrosoureainduced tumor in rats fed 0.2% SIT in the diet for 28 wk. There was a 39% reduction in the number of rats that developed the tumor and a 60% reduction in the number of tumors per rat with SIT feeding.Usually, the development of colon cancer is preceded by an increase in cell proliferation in the colonic mucosa, i.e., hyperplasia. Accordingly, this condition is considered to be a risk factor for the development of colon cancer (9). Several investigators examined the effect of dietary PS on colonocyte proliferation in mice (10) and rats (11). In these studies, cell proliferation was stimulated by including cholic acid in the diet and monitored by using 3 H-thymidine or bromodeoxy uridine. Feeding a 1-2% PS mixture, which was made up of 56% SIT, 28% campesterol, 10% stigmasterol and 6% dihydrobrassicasterol by weight, for 22 d resulted in normalizing the cholic aci...

Phytochemicals have been proposed to offer protection against a variety of chronic ailments including cardiovascular diseases, obesity, diabetes, and cancer. As for cancer protection, it has been estimated that diets rich in phytochemicals can significantly reduce cancer risk by as much as 20%. Phytosterols are specific phytochemicals that resemble cholesterol in structure but are found exclusively in plants. Phytosterols are absorbed from the diet in small but significant amounts. Epidemiological data suggest that the phytosterol content of the diet is associated with a reduction in common cancers including cancers of the colon, breast, and prostate. The means by which dietary phytosterols may be achieving these effects is becoming clearer from molecular studies with tumorigenic research models. Phytosterols affect host systems potentially enabling more robust antitumor responses, including the boosting of immune recognition of cancer, influencing hormonal dependent growth of endocrine tumors, and altering sterol biosynthesis. In addition, phytosterols have effects that directly inhibit tumor growth, including the slowing of cell cycle progression, the induction of apoptosis, and the inhibition of tumor metastasis. This review summarizes the current state of knowledge regarding the anticancer effects of phytosterols.

Work from our laboratory, as well as others, suggests a protective role of phytosterols (PS), especially beta-sitosterol, from colon, prostate, and breast cancer. Asians and vegetarians consume higher amounts of PS than Western societies. The latter societies have a higher incidence of these cancers than Asians and vegetarians. The aim of this study was to evaluate peanuts and its products as sources of PS in the American diet. Roasted peanuts contain 61-114 mg PS/100 g depending on the peanut variety, 78-83% of which is in the form of beta-sitosterol. Unrefined peanut oil contains 207 mg PS/100 g, which is similar to that of the US Department of Agriculture Nutrient Database. This value is higher than that of unrefined olive oil. Refining these oils results in reduction in PS concentration in the oil. This loss is greater in the case of olive oil than peanut oil. Further refining, such as deodorization, results in significant loss in PS, but hydrogenation after refining has a minimal effect on PS loss. Peanut butter, which represents 50% of the peanuts consumed in the United States, contains 144-157 mg PS/100 g. Peanut flour, which results from partial removal of oil from peanuts, contains 55-60 mg PS/100 g. The data suggest that peanuts and its products, such as peanut oil, peanut butter, and peanut flour, are good sources of PS.

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