Her skin was pale and she was irritable and apprehensive. At 16 months, the mother began feeding the child milk with reduced lactose rather than whole cow's milk. During the next month, the child gained 2 lb, 3.5 oz, diarrhea subsided, and symptoms of abdominal distress resolved. Neither parent has a food intolerance, although both are allergic to nonfood allergens. A full-term infant's birth weight should double by 5 months of age and triple by 1 year.
Healthy children tend to follow their appropriate percentile growth curves.
A marked deviation in growth may be caused by a physical illness, nutritional disturbance, or psychosocial difficulties. Although weight gain in this child was curtailed, there was only a slight delay in body length gain between 16 and 18 months. The infant maintained appropriate increases in head circumference, at approximately the 60th to 70th percentile. The differential diagnosis for decreased disaccharidase activity includes celiac disease, small bowel bacterial overgrowth, giardiasis, lactose intolerance, and milk protein allergy. The mechanism of allergy should not be confused with intolerance.