Diarrhea is one of the most common symptoms of food allergy, especially in children. In allergic people, the bowel tends to react to certain foods as though they were laxatives, unpredictably flushing out loose stools throughout the day. But being caught offguard is only part of the problem.

Prolonged diarrhea – lasting more than a week – leaves the body dangerously weak and dehydrated from loss of fluid and minerals like potassium. With too little water and nutrients, your muscles and nerves don't work. In children, diarrhea is especially risky – their bodies are too small to deal with drastic losses of water and minerals.

As a result, uncontrolled diarrhea can leave children as limp as a ragdoll. Or they can have convulsions. Diarrhea has several possible causes other than allergy. But if your doctor has ruled out infection or disease, you should consider food allergy. In children, milk is to blame for one out of these cases of diarrhea caused by food allergy.

For them, diarrhea is nature’s way of rejecting a food that it regards as harmful. ”Because cow’s milk is not a natural food for an infant, the body often tries to reject it with allergic reactivity, especially when a family tendency to allergy exist,” says Albert Rowe, Jr., M.D., as coauthor of the book Food Allergy (Charles C. Thomas, 1972).

Dr. Rowe mentions one study which that out of 140 children allergic to cow’s milk, 24 percent – about 1 out 4 – had diarrhea. In infants, breast milk nearly always relieves allergy to cow’s milk, especially if the nursing mother also avoids cow’s milk. When the children gets older, he or she may eventually be able to tolerate milk.

It may take 6 months, or it may take 12 years. Trial and error is the only way to tell. After milk, fruit and sugar are frequent causes of allergic diarrhea. Apparently, some people cannot tolerate fructose, the sugar found in honey and sweet fruits such as plum, apples and grapes. In still others, any kind of sugar causes diarrhea.

Two Swedish doctors report the cases of four people who has suffered diarrhea, abdominal pain and bloating for up to six week at a time. Between these episodes, they had milder discomfort. ”All had noticed an aggravation of symptoms whenever they had eaten fruits, or food containing appreciable amounts of cane sugar,” says the researchers. ”All patients were free from symptoms on a fructose free diet” (Acta Medica Scandinavica, vol. 203, no. 1-2, 1978).

In still other children, both milk and sugar must be avoid in order to diarrhea to let up. One group of pediatricians studied 75 children (all younger than one year) treated for diarrhea and other related problems. After several days on a milk free, soy based diet formula, some of the children were gradually given cow’s milk again, while the others received a soy formula free of milk and sugar.

The children drinking cow’s milk continued to have diarrhea indefinitely, while the children on milk free and sugar free formula got better fairly soon (Lancet, January 26, 1980). Occasionally, wheat and other cereals will cause diarrhea. Instructions for avoiding milk, sugar, cereals and others common causes of food allergy appear in Rotary Diets.

To test for any of those foods, the diet must be tried for at least one week and often longer, since it takes several days after food is eaten for it to be completely eliminated from the body. Sometimes food causes diarrhea during pollen season, but not during the rest of the year.

For example, a child may be able to drink milk or eat cereal all year around with no diarrhea, but will suffer several weeks of loose bowels when trees and grasses are pollinating in spring or summer. Parents of children with diarrhea should not hesitate to see a doctor, because of the immediate threat to health and the possibility of infection or disease.

Until the cause of diarrhea is brought under control, Lomotil or other antispasmodic drugs may be prescribed. See also Colic and Indigestion, Bloating and Abdominal (because eczema is also a common symptom of milk allergy, the entry Skin Inflammation (Atopic Dermatitis and Eczema) may be of help to some people).