Science Update

Phytosterol May Influence Cholesterol Absorption and Healthy Lipid Metabolism

Phytosterols are compounds present in most plant cells that contribute to the structure and stability of membranes. Phytosterols are fat-soluble compounds that are similar in structure to cholesterol (the most abundant sterol of animal cells). Hundreds of phytosterols have been identified from plant cells, including beta-sitosterol, brassicasterol, campesterol, and avenasterol. Phytosterols are present in legumes, seeds, and oily fruits, such as pistachios.

A recent review article highlights the role that phytosterols may have in promoting healthy lipid metabolism and cardiovascular health. Phytosterols may support healthy lipid metabolism during the process of digestion, although phytosterols and cholesterols compete in the intestinal lumen for incorporation into the mixed micelles destined to enter the enterocytes. This may lead to a potential dose-dependent inhibition of the absorption of some of the cholesterol molecules. Phytosterols may also inhibit some cholesterol absorption through their ability to co-crystallize with the cholesterol in the intestinal lumen, which can then be eliminated through the fecal route. Phytosterols can also reach the liver through the chylomicron pathway.

All of these factors, as described, have the physiological potential to lead to an increased uptake of plasma low-density lipoprotein (LDL) cholesterol levels in the facilitation of endogenous cholesterol synthesis. This may have the potential to lead to a reduction in measured plasma LDL cholesterol levels that appear to be associated with the amount of phytosterol ingested.

A 2% to 3% reduction in LDL cholesterol levels was observed in a study involving 300 mg per day to 400 mg per day of phytosterols. Another study reported an average reduction of 9% when participants supplemented with 1,500 mg per day and 2,000 mg per day. A third study reported that supplementation with 3 g of phytosterols daily led to an approximate 12% reduction of LDL cholesterol levels. The authors of the review article also reported that the potential effect of phytosterols on LDL cholesterol levels may be independent of initial concentrations of cholesterol and may therefore be beneficial for individuals with both low and high LDL cholesterol levels.

Another recently published review article described phytosterols and other molecules that may influence cholesterol absorption and support healthy lipid metabolism. Beta-glucan is a soluble fiber that is found in the cell walls of fungi, bacteria, yeasts, and certain plants, and it has been shown to support lipid metabolism. Beta-glucan was shown in a meta-analysis to significantly reduce LDL cholesterol levels in individuals with hypercholesterolemia. Psyllium is another source of fiber that has been shown to influence levels of LDL cholesterol levels by stimulating 7-alpha-hydroxylase and reducing the absorption of cholesterol in the intestinal lumen.

There are several mechanisms involved in the influence of lipid metabolism in the human body. Molecules such as phytosterols, psyllium, and beta-glucans may support healthy metabolism through the action of cholesterol absorption inhibition. Supplementation with phytosterols may support healthy lipid metabolism and cardiovascular health.

By Colleen Ambrose, ND, MAT