Chronic diarrhea is the most common sign of intolerance to cow's milk in children. In a previous study, Iacono and colleagues demonstrated that constipation may also be a sign of intolerance to cow's milk. They hypothesized that cow's milk may cause perianal lesions and painful defecation, resulting in constipation. In this double-blind, crossover study, they compared the effects of soy milk and cow's milk in children with chronic constipation.

Children younger than six years who had been referred to a subspecialist for treatment of chronic constipation were eligible for the study. Exclusion criteria were anatomic causes of constipation, constipation related to another disorder, prior anal surgery or the use of medications known to cause constipation. Constipation was defined as one bowel movement every three to 15 days, accompanied by abdominal symptoms such as pain with defecation. At baseline, children were being fed regular cow's milk, other dairy products or commercial formula made from cow's milk. Previous treatment with laxatives had been unsuccessful in all of the patients.

Sixty-five patients were included in the study and underwent a detailed history and physical examination, along with laboratory tests for total and milk-specific IgE antibodies and a rectal biopsy. Thirty-two children were then assigned to receive a soy-milk diet and 33 were assigned to receive a diet with cow's milk for the next two weeks. After a one-week washout period, the children's diets were reversed for two weeks. A response was defined as eight or more bowel movements during the two-week treatment period. Following the two study periods, the children with a response to the diet that was free of cow's milk were given the soy-milk diet for another month and then underwent a double-blind challenge with cow's milk. During the challenge, the child was randomly assigned to receive cow's milk or a placebo containing soy milk. Each child was observed closely and the challenge was stopped if there were no bowel movements for 72 hours and the patient had perianal lesions or abdominal pain.

During the first phase, none of the children given cow's milk responded; however, 21 of the children given soy milk responded. All those who had a response had at least one soft bowel movement daily after two to six days, with no discomfort and complete resolution of perianal lesions, erythema and edema. During the second two weeks when the dietary interventions were reversed, 23 children who received soy milk responded, compared with none who received cow's milk. When the 44 children were re-challenged with the double-blind, placebo-controlled component of the study, none who received the soy milk had a reaction, compared with all of those who had been given cow's milk.

The rectal biopsy specimens obtained at baseline showed one or more histologic alterations, including inflammatory changes and infiltration by eosinophils, in all 44 of the children who responded to the soy milk and in 12 children who did not respond. A second biopsy in 20 of the responders, done randomly one month after they began the diet without cow's milk, showed normal histology in eight patients and considerable improvement in 12. At baseline, 31 of the 44 responders also had abnormal results on immunologic testing compared with only four of the children who did not respond.

The authors conclude that chronic constipation can be a sign of intolerance to cow's milk in young children, even though chronic diarrhea remains the most common gastrointestinal manifestation of this intolerance. Hypersensitivity shown on immunologic testing also increased the probability that the constipation was diet-related.