ABSTRACT
Plant Sterols 279
Animal Sterols in Plants 281
Sources of Phytosterols 281
Phytosterols in Membranes 282
Phytosterols and Cholesterol-Lowering Functional Foods 282
Phytosterols and the Immune System 283
Clinical Examples for the Use of Phytosterols in Medicine 284
Phytosterols and Cancer 284
Sterols/Phytosterols and the Skin 285
Phytosterols and Eczema 286
Phytosterols in Cosmeceuticals-The Future? 287
Are Risks Entailed in Using Phytosterols? 288
Trends-From Insect to Plant to Skin 289
References 289
PLANT STEROLS
Sterols are natural components of cell membranes. Both animals and plants
produce them. Cholesterol is exclusively an animal sterol. Phytosterols play a
role in plants similar to that of cholesterol in humans and mammals by forming
cell membrane structures; they are consequently of importance for plant cell
growth. Structurally, phytosterols resemble cholesterol except that they are
always substituted at the C24 position in the sterol side chain (Fig. 1). Phytoster-
ols differ substantially in their intestinal absorption and metabolic fate, as they
are not synthesized in humans. They are also poorly absorbed and excreted
faster from the liver than cholesterol. This explains their low abundance in
Figure 1 Chemical structure of plant sterols and stanols. Plant sterols, of which campesterol, beta-sitosterol, and stigmasterol are the most abundant in nature are structurally
related to cholesterol, but they have a different side-chain configuration. Saturation of
the sterols with hydrogen leads to the formation of plant stanols such as campestanol
and sitostanol. [According to van Kerckhoffs et al. (7).]
human tissues. Over 40 phytosterols have been identified so far. The most
common plant sterols are beta-sitosterol, campesterol, and stigmasterol, which
are structurally very similar to cholesterol (Fig. 1). Plant stanols are the hydro-
genated counterparts of the respective common plant sterols, for example,
stigmastanol is the hydrogenated form of stigmasterol (1,2). The unsaturated
form, called sterols, is common and present in many plants. The saturated
form, called stanols, is found only in small amounts in cereals, fruits, and
vegetables (3).
