Q: Is it true that sorbitol-sweetened candy can cause gastrointestinal upset?

A: Yes. In fact, sorbitol, the sugar alcohol used as a sweetener in some "dietetic" foods, for many years has been used in large doses as a cathartic.

Several studies have documented gastrointestinal symptoms of sorbitol intolerance in children at doses of only about a third the amount used as a laxative. But until recently, it had been evaluated with adults only in one small study.

Researchers from Our Lady of Mercy Medical Center in the Bronx and New York Medical College, in Valhalla, N.Y., have reported on the effects of sorbitol on 42 healthy volunteers. Each volunteer was given 10 grams of sorbitol in a drink. That is the allotment in four or five sorbitol-sweetened mints, an amount not uncommonly consumed within a short time. The investigators then measured breath hydrogen every 15 minutes for four hours. A rise in breath hydrogen indicates that the sweetener was not absorbed and was broken down by bacteria in the large bowel. Over a six-hour period, they also noted symptoms commonly associated with sorbitol intolerance, including abdominal pain, bloating and diarrhea.

A significant rise in breath hydrogen was observed in 31 (74 percent) of the subjects, and clinical symptoms were experienced by nearly half of them. These symptoms were classified as mild in nine cases, moderate in four and severe in seven. Severity of symptoms began anywhere from 30 minutes to 3 1/2 hours after taking the sorbitol, and was associated with the amount of breath hydrogen excreted.

The authors of the study point out that over a two-year period, they treated 15 patients who had sorbitol intolerance masquerading as irritable bowel syndrome.

Besides the fact that sorbitol can cause discomfort to a significant number of individuals, it is not a calorie-free sweetener. While it takes longer to be absorbed, as much as 90 percent may be taken into the bloodstream and burned for energy or stored as fat.

Q: Can you explain why some diabetics, such as my husband, are advised by their physicians to monitor blood-sugar levels, while others continue to test only their urine?

A: Although we do not know specifically why your husband was told to keep track of his blood-sugar level, we can tell you the reasons why it is done.

For most diabetics, achieving blood-glucose levels as close as possible to the non-diabetic state is a major goal. Blood-glucose values are more reliable than urine testing in monitoring control of the condition.

The American Diabetes Association recently issued a policy statement that outlined the indications for self-monitoring of blood glucose. It was "strongly" recommended in three situations: in individuals receiving "intensive" insulin therapy, such as those using insulin pumps or taking multiple daily insulin injections; in women who are or are planning to become pregnant; and in individuals with insulin-dependent diabetes millitus who are prone to hypoglycemia and who may not experience the usual symptoms that accompany the drop in blood-sugar levels.

In four additional situations they believe that self-monitoring should be encouraged. These include routine management of individuals taking insulin, those in whom blood glucose is unsually high or low when sugar appears in the urine, in those who have unusual "insulin resistance" (they do not use insulin efficiently) and require large doses, and finally, for any diabetic who, with his or her doctor, is motivated to try to achieve better control or to change their drug therapy.

Q: Our supermarket continues to add new kinds of fruits and vegetables to its repertoire. Some come with suggestions for preparation, and I have tried a number. Others have no instructions, and I have no idea how to handle them. One such is jicama. Can you tell me what it is and how to prepare it?

A: Jicama gets its name from the Aztec word xicamatl and is also known as yambean. In Mexico, it is a common root vegetable. It can be cooked by first peeling away the skin and tough outer layer immediately underneath, then boiling, steaming or frying it as you would a potato. Just make sure to cook it only until it is tender. A 3 1/2-ounce serving contains about 45 calories.

The smaller roots can be eaten raw, either sliced into salad or served with a dunking sauce. If eaten raw, a whole cup of slices has 50 calories, mainly from carbohydrate. Both the raw and the cooked varieties provide some vitamin C and small amounts of the B vitamins.