Q. What is the difference between soda water and seltzer

A. Soda water is a general category that includes all beverages containing carbon dioxide, and flavored soft drinks as well as several types of unflavored waters such as club soda and seltzer. Seltzer is simply water that has been filtered and carbonated, while club soda has minerals added for taste. With the recent emphasis on consuming less sodium, producers of club soda have begun marketing sodium-free as well as regular club soda.

Q. My young son has something the pediatrician calls "toddler diarrhea." The doctor has ruled out any malabsorption disease or infection as the cause and has assured me that he will be fine by the time he is 3 or 4 years old, pointing out that according to the growth chart he is doing just fine for his age. But I am still concerned. Is there is anything I can do to resolve the problem?

A. Apparently your son's condition is of the type for which time and patience are the treatment. According to the newly published second edition of the "Pediatric Nutrition Handbook," authored by the committee on nutrition of the American Academy of Pediatrics, toddler diarrhea (also known as "sloppy stool syndrome" and a variety of other names) is the major explanation for problems of "loose stools" referred to gastroenterologists. For reasons that are unclear, incidence of the condition is on the rise.

The authors of the handbook believe that two different types of the problem exist. Both kinds usually begin between 6 months and 1 year of age, and are not associated with any identifiable problems in the intestinal tract. In both, growth is normal, but only one is responsive to diet.

Those who seem to respond to diet tend to have several characteristics. They have recently had an acute gastrointestinal infection with persistent watery stools well beyond the time that symptoms should have disappeared. These children seem to have some normal bowel movements and a relatively higher weight in relation to their height. Dietary histories suggest that they consume more calories than they need (not surprising in light of their weight-to-height status) and drink large amounts of liquids. In some cases, fat intake may be quite low. Generally, in these cases a more appropriate diet and a limiting of fluids, especially certain types which are more likely to provoke diarrhea, lead to relief of symptoms.

The other group, which does not respond to diet, tends to have been colicky infants and have anywhere from three to six mucus-containing stools a day, with equal numbers in the morning and evening. Usually there is a family history of some type of bowel problem and in about half the cases another sibling has been similarly affected. Gradual but complete recovery usually occurs between 3 and 4 years of age.

Q. Recently I had a stir-fry Chinese vegetable dish that contained lotus root, and I really enjoyed it. The root is sold in Oriental markets nearby, so I would like to begin using it in my own Chinese cooking. Can you tell me its nutritional value?

A. Ten slices of cooked lotus root, about one-fourth inch thick and 2.5 inches in diameter, contain 60 calories and more than one-third of the day's ascorbic acid. Lotus root also provides a little iron and some B vitamins and is a rich source of potassium.

If you have never used the root, which has a rather sweet taste and crisp texture, keep in mind that once scrubbed and peeled, it darkens quickly. For this reason, it should be kept under water until used. Also, it is best to parboil it for two or three minutes before adding it to the stir-fry mixtures. Fresh lotus root is generally most readily available during the winter months, but you can also buy it in dried form. Before using, it must be soaked in hot water for about 20 minutes to rehydrate it.