When it comes to lowering cholesterol, we may be throwing away the best part of citrus fruits, new research suggests.

The study found that certain compounds in the peels of tangerines and oranges significantly lowered "bad" LDL cholesterol in hamsters that had been living on a high-cholesterol diet.

The compounds, known as polymethoxylated flavones (PMFs), are antioxidants that belong to a group of plant chemicals called flavonoids. Flavonoids exist in a variety of fruits and vegetables, as well as tea and red wine.

Research suggests the compounds help guard against heart disease and cancer, and two other citrus flavonoids--hesperetin from oranges and naringenin from grapefruit--have shown early promise in lowering cholesterol.

The new study, published in the Journal of Agriculture and Food Chemistry, is the first to show that PMFs may lower LDL cholesterol, according to the authors.

The results from a pilot study suggest the benefits may extend to humans, and a larger clinical trial is underway to see whether a supplement combining PMFs and a form of vitamin E can help treat high cholesterol, the study's lead author, Dr. Elzbieta M. Kurowska, told Reuters Health.

Kurowska is vice president of research at Canadian nutraceutical company KGK Synergize Inc., which is already marketing Sytrinol, the supplement being used in the clinical trial.

London, Ontario-based KGK Synergize and the U.S. Department of Agriculture (USDA) funded the animal study.

According to Kurowska, PMFs are not soluble in water, so citrus juice contains only a small amount of the compounds. Orange zest, grated orange peel used to flavor foods, contains PMFs, but it would take eating the zest of about 25 oranges a day to reap a cholesterol benefit, the researcher noted.

In the hamster study, she and co-author John A. Manthey of the USDA found that a diet containing one percent PMFs cut the animals' LDL cholesterol by up to 40 percent. The researchers used the two PMFs most commonly found in citrus fruits, tangeretin and nobiletin.

For comparison, some of the hamsters were given a diet enriched with hesperetin and naringenin. These flavonoids, the researchers found, also lowered LDL cholesterol, but it took three times as much of them to yield the benefit seen with the PMFs.

Kurowska said it appears the compounds may work by lowering the secretion of cholesterol from the liver.

SOURCE: Journal of Agriculture and Food Chemistry, May 12, 2004.

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