Two new cholesterol-lowering margarines have been approved by the U.S. Food and Drug Administration as “foods.” Benecol (McNeil Consumer Health Care) contains hydrogenated sterols, primarily sitostanol derived from pine tree wood pulp. The other product is Take Control (Unilever), which contains naturally occurring unsaturated sterols, primarily sitosterol from soybean oil. The chemical structure of plant sterols resembles cholesterol. The stanol esters in Benecol are produced from sterols by hydrogenation and esterification with unsaturated fatty acids. Consultants for the Medical Letter on Drugs and Therapeutics reviewed the efficacy of these sterol-rich margarines in reducing low-density lipoprotein (LDL) cholesterol levels.

When plant sterols are administered orally, intestinal absorption of dietary and biliary cholesterol is decreased, and fecal excretion is increased. It appears that the poorly absorbed sterols compete with cholesterol for incorporation into mixed bile salt micelles, a prerequisite for uptake of cholesterol by enterocytes. The decreased supply of intestinal cholesterol available to the liver results in decreased production and increased excretion of LDL cholesterol precursors, thus decreasing LDL production. It is postulated that some patients do not respond to sterols because of the liver's attempt to increase cholesterol synthesis in response to decreased availability of cholesterol.

A double-blind, randomized trial compared plant sterol esters and sitostanol ester in margarine with a control margarine in normal and mildly hypercholesterolemic patients. After 3.5 weeks, the two enriched margarines had lowered LDL cholesterol levels by about 12 percent compared with the control margarine. Another crossover study with similar comparisons demonstrated a 6.7 to 9.9 percent reduction of LDL cholesterol levels when a sterol mixture containing 48 percent sitosterol in a full-fat (70 percent) margarine was used and compared with a control margarine.

Another double-blind trial in mildly hypercholesterolemic persons randomized participants to use margarine without sitostanol or the same margarine containing 3 g of sitostanol ester. After six months, 50 percent of the actively treated participants decreased their sitostanol intake to 2 g daily. After 12 months, the dosage of 3 g of sitostanol had decreased average LDL cholesterol levels from 160 to 134 mg per dL (4.14 to 3.50 mmol per L), compared with virtually no reduction in the control group. The daily dosage of 2 g of sitostanol in the second six months decreased LDL cholesterol levels from 153 to 138 mg per dL (3.96 to 3.58 mmol per L) at 12 months. The effect of sitostanol on HDL cholesterol and triglycerides was not statistically significant.

Sterol and stanol esters in margarine are well tolerated and do not affect the taste or texture of the margarine. Short-term studies have not shown adverse effects on routine laboratory parameters. High serum concentrations of plant sterols have been associated with premature coronary disease. Patients with inherited sitosterolemia are known to develop xanthomas and premature ischemic heart disease. Because stanols are absorbed less than sterols, plasma serol concentrations should be lower with Benecol than with Take Control. Both margarines may decrease plasma concentrations of antioxidants.

Take Control contains 1,120 mg of sitosterol per one-tablespoon serving (50 calories per serving). The manufacturer recommends one to two tablespoons daily. Benecol contains 1.5 g of plant stanol ester (sitostanol) per one and one-half teaspoon serving (45 calories per serving). The manufacturer recommends three servings daily. Both margarines cost about five times as much as ordinary margarine.

The consultants conclude that sterolenriched margarines can lower LDL cholesterol by 10 to 15 percent. It is unknown if their use will lower the morbidity and mortality from coronary heart disease. The beneficial effects of lowering LDL cholesterol levels may be offset by increased plasma concentrations of plant sterols that may be atherogenic.