Q: I am one of those people who eats my weight in asparagus when it is in season. But I have always wondered about what causes a certain odor in my urine after I eat it. Can you tell me what it is and whether it is harmful?

A: We commonly associate the pervasive and rather disagreeable odor of cooking cabbage and other members of the brassica family with sulfur compounds but not with asparagus. In fact, the characteristic odor that asparagus imparts to the urine is also believed to be explained by the presence of sulfur-containing compounds, of which two have been identified. The "raw materials" in asparagus from which these two compounds are produced in the body have yet to be identified, but there is no reason to think that the odor is a marker for any potentially harmful compound.

Asparagus provides considerable amounts of both vitamins A and C. Four large stalks, containing just 20 calories, would offer nearly 20 percent of the Recommended Dietary Allowance (RDA) for the former and, on average, 40 percent of the RDA for the latter. Of course, Vitamin C can be destroyed rather easily. Brief cooking in small amounts of water will maximize retention not only of Vitamin C but of other water-soluble nutrients as well.

Q: I recently began to both roller-skate and ice-skate. Can you tell me how many calories I burn doing each of these sports?

A: Both ice skating and roller skating at a speed of 9 miles per hour burn about .042 calories per pound of body weight per minute. To figure out how many calories you burn, simply multiply your weight by that factor and then by the length of time you skated. Thus someone weighing 130 pounds would burn about 245 calories in 45 minutes, while a person who weighed 190 pounds would burn about 360 calories in the same time.

You will want to estimate whether you are skating significantly faster or more slowly than the rate associated with that level of energy expenditure. If you are ice-skating on a regulation hockey rink, 9 1/4 laps around the rink is about a mile.

If you are playing hockey, which involves more vigorous activity, you will burn about .066 calories per pound of weight per minute of play.

Q: My doctor has said that he would prefer that I get even more than the Recommended Dietary Allowance of 800 milligrams (mg.) of calcium a day -- as much as 1,200 to 1,400 mg. a day. Before I begin taking a supplement, I would like to have some idea of how much I am getting in my diet.

A: As you know, dairy products are the major sources of calcium in the diet, and without them it is difficult to consume as much as 800 mg. a day, unless you consistently eat reasonably large servings of a few other foods. A cup of milk provides 300 mg. and a cup of plain, low-fat yogurt somewhat more, about 415 mg. Hard cheeses contain between 150 and 270 mg. per ounce. But part-skim ricotta, at 335 mg. per half-cup, is a particularly rich source. At the other extreme, the same amount of low-fat cottage cheese contains only about 75 mg.