Q. Why does asparagus seem to make my urine smell funny?

A. Asparagus is a healthy, delicious and easy-to-prepare green vegetable. Within a short time after eating it, some folks complain that their urine has a pungent odor, often compared to rotting cabbage. The effects of "asparagus urine" are temporary and harmless.

It is uncertain whether the production of this odor is universal. Several studies discussed in the April 2001 issue of the journal Drug Metabolism and Disposition try to shed light on this issue. For example, in tests of 800 Britons, approximately 43 percent produced the odor. And all 103 French citizens tested produced the odor, so there may be an ethnic or genetic component at work here.

The situation is more complicated than it appears on the surface. Scientists are unsure whether people have different urinary responses to asparagus or whether some folks just lack the ability to smell the odors produced by asparagus. In a study of 307 Israelis, 90 percent could not smell the asparagus generated odor in urine and in a study of 98 Chinese subjects, 76 percent were unable to detect it even though it was present.

A later American study suggests that both phenomena coexist. Some people are "excretors" (their urine smells after eating asparagus) and some are "nonexcretors" (no smell). Some people are "perceivers" (able to smell the odor), while others are "nonperceivers" (unable to smell the odor, even though it exists).

This complicated issue requires further investigation.

Scientists are still learning what causes "asparagus urine." Many believe the odor is generated by a combination of sulfur compounds produced when certain amino acids in asparagus are broken down during digestion. One study found six sulfur compounds present in the urine of known excretors, but not in nonexcretors. Non-excretors may lack the enzyme needed to break down amino acids in asparagus into the smelly compounds in the urine.

Don't avoid asparagus due to this side effect. It's a powerhouse of nutrients. Asparagus is full of folic acid, vitamins A and C, potassium and fiber.

Several phytonutrients in asparagus have shown promise in inhibiting growth of cancer cells. A substance in asparagus helps strengthen arteries and increases circulation to the lower limbs. Asparagus also contains a substance that helps the intestines produce "friendly bacteria" to improve digestion.

Amy Tousman is a registered dietitian and certified diabetes educator with Nutrition Unlimited in Kailua. Hawai'i experts in traditional medicine, naturopathic medicine and diet take turns writing the Prescriptions column. Send your questions to: Prescriptions, Island Life, The Advertiser, P.O. Box 3110, Honolulu, HI 96802; fax 535-8170; e-mail islandlife@honoluluadvertiser.com. This column is not intended to provide medical advice.