Lactose intolerance is a chronic condition that affects the way the gut moves milk and dairy products through the body. This disorder prevents the body from breaking down or digesting lactose, a sugar found in milk and dairy products.1-4 Different from a milk allergy, which is characterized by an abnormal and, sometimes, life-threating response by the body’s immune system, lactose intolerance happens when the small intestine does not make enough of the digestive enzyme lactase.4,5 This enzyme helps break down the lactose in foods for absorption by the body. People with this condition typically experience unpleasant gastrointestinal (GI) symptoms after consuming dairy products, such as bloating, upset stomach, diarrhea, and/or gas.1-3 Here, we review research on lactose intolerance, addressing its types, causes, management, and risks.
TYPES AND CAUSES OF LACTOSE INTOLERANCE
There are three main types of lactose intolerance—primary, secondary, and congenital.5 Each type is characterized by the different factors that cause the lactase deficiency.
Primary lactose intolerance. People who develop this type, also known as lactase nonpersistence, produce enough lactase as babies, but that production drops sharply as they grow, especially during the first 10 years of life.5-7 This is the most common type of lactose intolerance. Because infants get all their nutrition from milk, lactase production is essential to their survival. But as they transition from milk to solid foods, the amount of lactase they produce normally drops. Typically, children produce enough of this enzyme to digest the amount of dairy in a typical adult diet, but people with primary lactose intolerance do not.
Secondary lactose intolerance. This form of lactose intolerance is not genetic. Instead, it occurs when the small intestine decreases lactase production after an illness, injury, or surgery involving the small intestine.5 Conditions that can cause secondary lactose intolerance include intestinal infection, celiac and Crohn’s diseases, and bacterial overgrowth. Certain medicines, radiation therapy, or invasive procedures can also injure the small intestine and trigger this type of lactose intolerance.6-8 This is the only form of lactose intolerance that isn’t considered chronic. Over time, treatment of the underlying disorder or injury may restore lactase production levels.7
Congenital lactose intolerance. Also known as developmental lactose intolerance, this is the rarest form of lactose intolerance.5,6,8 Some babies are born with the inability to produce lactase due to an autosomal recessive pattern of inheritance in which both parents pass on the same gene variant to their child.5 However, developmental lactose intolerance can also be nongenetic, such as in premature infants, and in these cases it is usually a short-term problem that goes away.1
ETHNICITY AND LACTOSE TOLERANCE
Lactose intolerance is common in adults worldwide and is rarely dangerous. It is estimated that about 68 percent of the world and about 30 million American adults have some degree of lactose intolerance by age 20.2,3 In the United States, this condition is most common in Asian Americans, African Americans, Mexican Americans, and Native Americans.5,7 This trend is largely attributed to the diets of their ancestors. For example, dairy products were a key dietary component among the ancestors of people of northern European descent, which contributed to an evolutionary pressure to maintain the ability to digest lactose throughout adulthood. In other cultures in which dairy consumption was much less prevalent, maintaining the ability to digest lactose after infancy was not necessary from an evolutionary standpoint.7
Unfortunately, there is no known way to prevent most cases of lactose intolerance, and its management depends on its type and cause. For many people with the condition, an elimination diet—one that removes or avoids milk products—is the first step to understanding lactose-induced flare ups and managing symptoms.1-4 There are options for people with lactose intolerance who wish to consume dairy.
Colonic adaptation. The body’s gut microbiome helps digest food and can play a role in how the body processes dairy.10 New research shows that Bifidobacterium and Lactobacillus—two types of lactose-fermenting bacterial species that can digest and use lactose as a source of energy—increase the levels of lactase in the gut.9 It is thought that regular lactose intake stimulates the growth of these beneficial bacteria as a prebiotic effect, opening the door for some lactose intolerant individuals to experience less severe and less frequent symptoms by gradually and progressively introduce lactose-containing foods. This suggests an adaptation mechanism known as colonic adaptation occurs during progressive and sustained intake lactose.11
Controlling symptoms through dietary changes. In the past, people who were lactose intolerant were told to avoid dairy products altogether, but health experts now suggest they try different dairy foods to see which, if any, may cause fewer symptoms.1,10 Most people with lactose intolerance have set amount of lactose-containing foods they can consume before experiencing any symptoms. Through trial and error, they can learn what amount and type of lactose-containing products they can tolerate.9,10 For example, high-lactose foods (which contain between 5–8 grams of lactose) include milk, soft cheeses, yogurt, and ice cream. Low-lactose foods (which contain between up to 2 grams of lactose) include condensed milk, half and half, sour cream, sherbet, and aged or hard cheeses.3 Although the body’s production of lactase will not increase, the gut may be able to become more tolerant to lactose by modifying the microbiome.10,11
Supplements. There are several over-the-counter medications, which can come in the form of pills, liquid drops, and powders, that can help prevent the symptoms of lactose intolerance flare ups.4,5,9,10 These remedies usually contain lactase and should be taken just before a meal or snack. However, these products don’t help everyone with the condition. Some GI experts have recommended taking probiotics. However, the direct use of probiotics for the management of lactose intolerance is still in debate; thus, people with lactose intolerance should consult with their doctor before trying this treatment route.5,9,11
For some people,. completely cutting dairy products out of the diet may result in certain nutritional deficiencies, such as calcium.3 Since milk and foods made with milk are the most common source of calcium, some people with this condition may need to take a calcium supplement. However, other good calcium food sources include sardines, leafy greens, fortified orange juice, beans, and tofu.3
Lactose intolerance affects nearly two-thirds of the world’s population. People with this chronic condition have difficulty producing lactase, an important digestive enzyme, which results in unpleasant GI symptoms when lactose-containing foods are consumed. There are factors that make certain populations more susceptible. There are ways to manage this disorder. New research indicates that gradually and consistently incorporating lactose-containing food into one’s diet may increase the body’s tolerance to lactose by supporting certain healthy gut bacteria.
Editor’s note: If you experience symptoms of lactose intolerance, consult with a licensed healthcare professional to determine the best management plan for you.
1. Lactose intolerance. Johns Hopkins Medicine website. https://www.hopkinsmedicine.org/health/conditions-and-diseases/lactose-intolerance. Accessed 1 Apr 2022.
2. Medline Plus. Lactose intolerance. 11 Aug 2021. National Library of Medicine – Medline Plus website. https://medlineplus.gov/lactoseintolerance.html. Accessed 1 Apr 2022.
3. Cleveland Clinic website. Lactose intolerance. Updated 1 Dec 2019. https://my.clevelandclinic.org/health/diseases/7317-lactose-intolerance. Accessed 1 Apr 2022.
4. Szilagyi A, Ishayek N. Lactose intolerance, dairy avoidance, and treatment options. Nutrients. 2018;10(12):1994.
5. Mayo Clinic Staff. Updated 5 Mar 2022. Lactose intolerance. https://www.mayoclinic.org/diseases-conditions/lactose-intolerance/symptoms-causes/syc-20374232. Accessed 5 Apr 2022.
6. Mayo Clinic Staff. Milk allergy. Updated 12 Jun 2020. Mayo Clinic website. https://www.mayoclinic.org/diseases-conditions/milk-allergy/symptoms-causes/syc-20375101. Accessed 5 Apr 2022.
7. Storhaug CL, Fosse SK, Fadnes LT. Country, regional, and global estimates for lactose malabsorption in adults: a systematic review and meta-analysis. Lancet Gastroenterol Hepatol. 2017;2(10):738-746.
8. National Institute of Diabetes and Digestive and Kidney Diseases website. Updated Feb 2018. Symptoms & causes of lactose intolerance. https://www.niddk.nih.gov/health-information/digestive-diseases/lactose-intolerance/symptoms-causes. Accessed 5 Apr 2022.
9. Toca MDC, Fernández A, Orsi M, et al. Lactose intolerance: myths and facts: an update. Arch Argent Pediatr. 2022;120(1):59-66.
10. Micic D, Rao VL, Rubin DT. Clinical approach to lactose intolerance. JAMA. 2019;322(16):1620
11. Forsgård RA. Lactose digestion in humans: intestinal lactase appears to be constitutive whereas the colonic microbiome is adaptable. Am J Clin Nutr. 2019;110(2):273–279.