Sterol intake reduction

The cholesterol-lowering properties of dietary plant sterols have been known for decades (Best et al., 1954 Peterson, 1951 Poliak, 1953), due specifically to reductions in cholesterol absorption. Inverse correlations between plant sterol intake and cholesterol absorption have been reported in animals (Carr et al., 2002 Ntanios and Jones, 1999) and humans (Ellegard et al., 2000). The exact mechanism by which plant sterols inhibit cholesterol absorption is unclear, and several mechanisms of action have been proposed, including (1) competition with cholesterol for solubilization in micelles within the intestinal lumen, (2) cocrystallization with cholesterol to form insoluble crystals, (3) interaction with digestive enzymes, and (4) regulation of intestinal transporters of cholesterol. 

It is still a matter of controversy whether plant sterols and stanols are equally efficient in reducing cholesterol levels [28]. Some studies have shown that despite their different bioavailability, there is no clinical relevance with regard to their effect on total cholesterol, LDL-c, HDL-cholesterol, or triglyceride levels [25, 29]. Nevertheless, other authors have suggested that the differences in efficacy between plant sterols and plant stanols remain in the long-term interventions rather than in the shortterm studies [30]. For instance, in a recent meta-analysis of randomized placebo-controlled trials, decreases in LDL-c concentrations were dose-dependent for plant stanols but not for sterols. Similarly, intakes of plant stanols higher than 2 g day have been associated with additional and dose-dependent reductions in LDL-c [26]. Yet, this effect remains questionable [29]. It has been proposed that the difference in efficiency between these two compounds may be explained by the fact that plant stanols may reside longer in the intestine due to their lower absorption [31]. 

Several factors can influence the overall effect of plant sterols and stanols. Naumann et al. [32] reported that men are slightly more sensitive to PS intake than women, although the responsible mechanism for this difference is unknown. Another factor that may influence the efficiency of PS involves the baseline levels of plasma lipids [25, 32, 33]. For example, subjects with high and very high baseline levels showed stronger reductions in LDL-c levels than subjects with levels near optimal clinical concentrations [25, 33]. However, these effects could not be reproduced by other authors [34]. Similarly, controversial effects are seen on the improvement of other lipid parameters as HDL-cholesterol concentration increases in subjects with low baseline levels and decreases in those subjects with initially high levels [32], These differences suggest that people with an unfavorable ratio of total to HDL-cholesterol would especially benefit from PS consumption. 

Plant sterols (phytosterols), especially 4-desmethyl sterols, have recently gained much scientific and commercial interest due to the introduction of plant sterol-enriched foods and dietary supplements with marked serum cholesterollowering efficacy. Due to the structural similarity between cholesterol and 4-desmethyl plant sterols, the intake of optimal amounts of plant sterols and stanols (saturated sterols) lowers intestinal cholesterol absorption and results in a 6-15% reduction in semm LDL cholesterol concentrations. 

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