Phytosterols are naturally occurring plant compounds found in vegetables and legumes. They have a chemical structure similar to cholesterol, but inhibit the absorption of cholesterol in the intestine. Many studies have found that esterified phytosterols added to margarine can lower blood levels of cholesterol.

In a recent study, researchers asked 15 people with elevated cholesterol levels to eat four different dietary treatments, each for a 21-day period. Dietary treatments included 1.8 g per day of unesterified plant sterols, hydrogenated sterols (stanols), a 50:50 mix of sterols and stanols, and corn starch (as a placebo) mixed into butter. The total diet composition was precisely defined and provided to all subjects throughout the study.

Researchers found that sterols reduced cholesterol absorption by 56%, compared with 34.4% and 48.9% for stanols and the 50:50 combination of sterols and stanols, respectively. The placebo had no significant effect. As compared to the placebo, total blood cholesterol levels declined by 7.8%, 11.9% and 13.1%, while LDL (“bad”) cholesterol levels decreased by 11.3%, 13.4% and 16%, respectively, when the subjects consumed sterols, stanols and the combination.

The authors conclude that the unesterified plant sterols and stanols equivalently reduced blood levels of total and LDL cholesterol, but that the sterols were most effective in suppressing cholesterol absorption. Plant sterols have also been studied for their benefits to the immune system.

American Journal of Clinical Nutrition, 2002;76:1272-1278.