Q. I've heard conflicting information about the nutritional value of mushrooms. Can you set me straight?

A. Their main assets may be that they enhance the flavor of foods they accompany and are low in calories. A half-cup of raw sliced mushrooms provides about nine calories, a little more than 70 percent of them from carbohydrates and the rest from protein. Beyond that, they offer small amounts of B vitamins and are a good source of potassium.

The white mushroom is the most commonly available in markets in this country. vor of mushrooms and their effectiveness as a flavor-enhancer for other foods is explained by the large amounts of glutamic acid, a chemical relative of monosodium glutamate. Glutamic acid is also one of the two amino acids in the artificial sweetener aspartame.

Q. Could you please give me an update on the current status of sulfites in the food supply?

A. At present, the Food and Drug Administration requires food labels to reveal the use of sulfites on certain packaged fruits and vegetables. It has also proposed that manufacturers disclose the use of sulfites on the labels of other packaged foods where additives introduced at an earlier stage of processing are detectable in the finished product. And recently it published a proposed rule to ban the use of sulfites on raw fruits and vegetables served at restaurant and supermarket salad bars.

Meanwhile, the use of sulfites in fresh produce has dropped. According to a survey conducted by the Fresh Fruit and Vegetable Association, only 4.4 percent of suppliers reported continued use of sulfites.

As for health problems related to sulfites, approximately 300 reactions have been identified, the most commonly reported symptom being difficulty in breathing. Two-thirds of the reactions were considered serious and the rest moderate. Of the 17 deaths in which sulfites were implicated, the FDA has concluded that eight were probably associated and two possibly associated with food; two possibly associated with sulfite-containing drugs; and five probably unrelated.

An Ad Hoc Advisory Committee on Hypersensitivity to Food Constituents is currently evaluating the use of sulfites and of safe alternatives. Decisions already made by that committee include support for FDA and Bureau of Alcohol, Tobacco and Firearms (BATF) proposals. They would require labeling of foods or alcoholic beverages containing more than 10 parts per million (ppm) of sulfites. The committee also recommends rescinding the Generally Recognized as Safe status for sulfite use on fresh produce. It has recommended that the proposal be extended to cover fresh potatoes and that sulfites in "food preserver/fresheners" be banned as retail products for home uses such as dehydrating fruits.

There are no less than seven categories of uses for sulfites. As with other additives that have come under fire, it is impractical to consider banning the additive completely, because there are no safe and totally acceptable alternatives for some of the functions it serves. In these cases, the committee has proposed that maximum guidelines be set and minimum use encouraged. Because as many as one million Americans may be sulfite sensitive, this is obviously an important public-health concern -- but one without a simple solution.

Q. I saw a television commercial recently that claimed cream cheese has only half as many calories as butter. I always thought of it as a high-fat food. Am I wrong?

A. It is true that an ounce of cream cheese contains about 100 calories, while the same amount of butter has about twice that amount. Nonetheless, the fact is that about 90 percent of the calories in cream cheese come from fat. And like the fat in butter, it is highly saturated. Moreover, there is a tendency to use more cream cheese than butter to spread on bread or crackers. So the actual difference in the number of calories consumed could be very small.