Misunderstandings related to lactose intolerance and how to effectively manage this condition can lead to the unnecessary avoidance of dairy foods, which can compromise nutrient intake, especially calcium, and health. Part of this misunderstanding may be related to failure to appreciate the differences between lactose maldigestion and lactose intolerance. Primary lactose maldigestion is a normal, genetically-controlled decline in the intestinal activity of lactase, the enzyme necessary to digest lactose (milk sugar). This decline occurs at variable periods after weaning, depending on an individual’s genetic background. Lactose intolerance refers to the gastrointestinal symptoms associated with the incomplete digestion of lactose. Individuals with lactose maldigestion may or may not develop symptoms (i.e., lactose intolerance).

Common symptoms of lactose intolerance include abdominal pain, bloating, flatulence, and diarrhea. The severity of symptoms varies with the amount of lactose consumed in relation to the amount of lactase. Cultural and psychological attitudes can also influence perceived tolerance to lactose-containing foods. Self-diagnosis of lactose intolerance is not recommended as it can lead to unnecessary dietary restrictions, expense, nutritional shortcomings, and the missed opportunity to diagnose other manageable disorders (e.g., irritable bowel syndrome, celiac disease, cow’s milk protein allergy). The breath hydrogen test is the “gold standard” for diagnosing lactose maldigestion and intolerance. A positive diagnosis of lactose maldigestion does not necessarily mean that an individual will experience symptoms of lactose intolerance.

Approximately 25% of the U.S. adult population and 75% of the world’s population are estimated to be lactose maldigesters. However, the percentage of lactose maldigesters who are lactose intolerant remains to be objectively determined. In general, lactose intolerance tends to be grossly overestimated.

The goal for managing lactose intolerance is to remain symptom-free while meeting nutrient needs, especially for calcium, a nutrient often limited in many people’s diets. Management strategies should be individualized and periodically reevaluated. Strategies to improve tolerance to lactose include eating yogurt with live, active cultures and aged cheeses such as Cheddar and Swiss, and using lactose-free milk and other milk products and exogenous lactase in tablets or liquid form. Also, repeated exposure to lactose-containing foods (e.g., consuming less than 1/2 cup of milk and gradually increasing the amount) may improve tolerance through colonic adaptation.

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