Q: How common are allergic responses to food in very young children?

A: Not very, according to a recent study by Dr. S.A. Bock of the National Jewish Center for Immunology and Respiratory Medicine in Denver. The study involved 480 children who received their newborn care at a single pediatric clinic. They were followed until age 3, or beyond, if adverse reactions to a food continued after that year.

Parents' subjective views about the existence of an allergy was not always confirmed by testing. At each regular visit, parents were asked about the child's diet and whether any allergic response had been noted. Foods thought to cause problems were eliminated until symptoms disappeared. Then, unless there was danger of a serious reaction, the foods were later re-introduced in tiny amounts. The portions were gradually increased until either a reaction occurred or a normal serving was eaten without ill-effect.

This way of testing is called an "open challenge." When it failed to produce objective gastrointestinal or skin symptoms, a blind challenge was administered. This means that the food was given in dry form, hidden in another food, in increasing amounts until a reaction occurred or until a reasonable amount produced no symptoms.

Using these testing methods, the most commonly reproduced symptoms were associated with fruit or fruit juices. Fifty-six of 75 children whose parents believed they were sensitive demonstrated a response to an open challenge. Fruits or juices most often responsible included orange, tomato, apple and grape.

Besides this, of 133 children whose parents thought they had untoward reactions to food, sensitivity could be confirmed in 37 (28 percent) of them. The food most commonly implicated was milk (25 cases). No other single food affected more than four children.

Most striking was the finding that the majority of foods could be consumed again within nine months of being identified as the cause of the reaction. However, symptoms associated with fruits and juices, which appeared later -- on average at 15 months -- tended to last longer.

Q: Does breast milk protect infants against colic?

A: A study of 964 healthy infants, ranging from 2 to 52 weeks old, found no such link. Researchers from the University of Southern California School of Medicine and the Southern California Permanente Medical Group define colic as recurrent episodes of unexplained crying and irritability for at least one week in infants between 2 and 17 weeks old.

In each of three groups -- those being breast-fed, those on iron-fortified formula and those on a combination of the two -- about 20 percent of the infants experienced colic. But in a fourth group -- those fed on nonfortified formula -- the figure was 30 percent. There is no apparent reason for the higher rate, but investigators speculate that pediatricians or parents may have taken infants who were experiencing colic off the iron-containing formula, thinking that iron may have been the offending ingredient.

Consumption of cow's milk by the mother is sometimes thought to be associated with colic, resulting from cow's-milk proteins being transferred to the infant in the mother's milk. But there was no difference in the amount of colic between those whose mothers did and did not drink milk.

Q: I know that sorbitol is a sugar alcohol that is eventually absorbed and contains calories. My question is: Does sorbitol-sweetened gum cause cavities?

A: Generally not, judging from research findings. One small study recently showed that gum sweetened with sorbitol may even help offset the decay-causing potential of snack foods.

Five volunteers were fitted with a replacement for a missing molar. Beside it, next to another tooth, was placed an electrode on which plaque would form. Subjects were given two minutes to eat snacks harmful to teeth: a chocolate bar, raisins, a cream-filled chocolate cookie, an iced chocolate cupcake and cherry pie. The acidity of the plaque, an indicator that bacteria were digesting the carbohydrate, was measured continuously for two hours. It increased within 15 minutes after eating and had not returned to baseline at the end of the measurement period.

In a second test, the snacks were again consumed over two minutes. Two small water rinses were given in rapid succession to wash away loose food particles. The subjects were given one stick of sorbitol-sweetened gum to chew for 10 minutes. Acidity was recorded from that point for 40 minutes. In all cases, the acidity rose dramatically as before, and the water rinses had no effect. With chewing gum, however, values quickly returned to the less acidic pre-test levels.