ABSTRACT

Lactose intolerance is due to reduced levels of lactase in the small intestine. This chapter reviews clinical aspects of lactose intolerance and nutrition, and the population distribution of high and low lactase levels. It focuses on progress in understanding the structure and function of lactase and its regulation. The chapter argues that although milk intolerance is a frequent problem in human adults, it is not a disease, nor an abnormality, but the normal condition for most humans. A variety of terms has been used to describe clinical symptoms induced by the ingestion of milk and/or milk products. Typical complaints include abdominal pain, cramps or distention, nausea, flatulence, and diarrhea; in children and adolescents, vomiting may predominate. The diagnosis of lactose malabsorption and its pathogenesis is based on a combination of clinical findings and the results of appropriate tests. Human congenital lactase deficiency, present from birth, is extremely rare and inherited as an autosomal recessive gene.