Review Dietary and biological factors influencing lactose intolerance O. Brown-Esters, P. Mc Namara, D. Savaiano * Department of Nutrition Science, Purdue University, 700 W. State Street, West Lafayette, IN 47907-2059, USA article info Article history: Received 19 January 2011 Received in revised form 1 August 2011 Accepted 18 September 2011 abstract The number of Americans affected by lactose intolerance is estimated to be between 30 and 50 million people (NDDIC, 2005). Lactose intolerance is the symptoms experienced when the dose of lactose exceeds the digestive capacity of intestinal lactase (lactose maldigestion). Symptoms of intolerance typically include stomach discomfort, excessive flatulence and soft stool or diarrhea and are dependent on dose of lactose, transit time (influenced by meal composition), and colonic flora adaptation. Modest doses of lactose consumed with a meal on a regular basis are often very well tolerated. Lactose maldi- gestion may be caused by primary (most common), secondary, or congenital lactase non-persistence. Lactose maldigestion should not be thought of as a disease and is not a reliable indicator of lactose intolerance. The hydrogen breath test has become the most reliable method to diagnose lactose maldigestion. Ó 2011 Elsevier Ltd. All rights reserved. Contents 1. Introduction ....................................................................................................................... 98 2. Etiology of lactose maldigestion ...................................................................................................... 99 2.1. Primary lactase deficiency ...................................................................................................... 99 2.2. Secondary lactase deficiency ................................................................................................... 99 2.3. Genetics and single nucleotide polymorphisms ............................................. ...................................... 99 3. Diagnosis ......................................................................................................................... 99 3.1. Hydrogen breath test .......................................................................................................... 100 3.2. Clinical history .............................................................................................................. 100 4. Lactose intolerance and perceived lactose intolerance ..................................................................................100 5. Management of lactose intolerance ...................................................................................................100 5.1. Dose and adaptation ......................................................................................................... 100 5.2. Gastrointestinal transit ........................................................................................................ 101 5.3. Yogurt and other alternatives .................................................................................................. 101 6. Conclusion ........................................................................................................................ 101 References ..................................................................................................................... 101 1. Introduction All mammals lose most of their lactase (the enzyme that breaks down lactose) intestinal activity post-weaning. This loss is geneti- cally controlled. It is unique that several minority populations of humans sustain intestinal lactase activity at relatively high levels throughout life; the control of this enzyme maintenance appears to be due to genetic single nucleotide polymorphisms. A number of these polymorphisms have been identified. Low lactase activity (also misnamed lactase deficiency) is the norm for approximately 75% of adult (post-weaning) humans. This low activity can result in lactose maldigestion (thus individuals are called maldigesters) and symptoms of gastrointestinal distress (lactose intolerance) if lactose consumed exceeds the ability of the GI tract to digest the dose. Estimates of the number of Americans affected by lactose * Corresponding author. Tel.: þ1 765 427 7826; fax: þ1 765 494 0674. E-mail address: savaiano@purdue.edu (D. Savaiano). Contents lists available at SciVerse ScienceDirect International Dairy Journal journal homepage: www.elsevier.com/locate/idairyj 0958-6946/$ e see front matter Ó 2011 Elsevier Ltd. All rights reserved. doi:10.1016/j.idairyj.2011.09.010 International Dairy Journal 22 (2012) 98e103