Lactose malabsorption and intolerance: pathogenesis, diagnosis and treatment

Abstract

Lactose malabsorption is a common condition caused by reduced expression or activity of lactase in the small intestine. In such patients, lactose intolerance is characterized by abdominal symptoms (e.g. nausea, bloating, and pain) after ingestion of dairy products. The genetic basis of lactose malabsorption is established and several tests for this condition are available, including genetic, endoscopic, and H2-breath tests. In contrast, lactose intolerance is less well understood. Recent studies show that the risk of symptoms after lactose ingestion depends on the dose of lactose, lactase expression, intestinal flora, and sensitivity of the gastrointestinal tract. Lactose intolerance has recently been defined as symptoms developing after ingestion of lactose which do not develop after placebo challenge in a person with lactose maldigestion. Such blinded testing might be especially important in those with functional gastrointestinal diseases in whom self-reported lactose intolerance is common. However, placebo-controlled testing is not part of current clinical practice. Updated protocols and high-quality outcome studies are needed. Treatment options of lactose intolerance include lactose-reduced diet and enzyme replacement. Documenting the response to multiple doses can guide rational dietary management; however, the clinical utility of this strategy has not been tested. This review summarizes the genetic basis, diagnosis, and treatment of lactose malabsorption and intolerance.

Keywords: Blinded testing; FODMAP; genetic test; hydrogen breath test; irritable bowel syndrome; lactase deficiency; lactose intolerance; lactose malabsorption; lactose maldigestion; multiple-dose testing.

Figure 1.

Interpolated frequency of the lactose malabsorption phenotype in the Eastern Hemisphere Dots indicate locations of data collection. In regions with few data points (for instance Australia) this map is less reliable. Figure modified from Itan et al.

Figure 2.

Diagnostic algorithm for diagnosing lactose malabsorption and lactose intolerance Diagnosis of lactose malabsorption is a pre-requisite for diagnosis of lactose intolerance (LI). Tests of malabsorption (genetic, biopsy) should be followed by a test of intolerance before lactose restriction is recommended. Blinded testing at multiple doses in the home setting may help guide rational dietary management; however, protocols still need to be established. LI, lactose intolerance; IBS, irritable bowel syndrome; SIBO, small intestinal bacterial overgrowth.