Applied Evidence

Do probiotics reduce adult lactose intolerance? A systematic review

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Purpose: To assess the efficacy of oral probiotics in adults with lactose intolerance through a systematic review of its effects on symptoms and breath hydrogen tests, and whether adding probiotics to nonfermented dairy products decreases lactose intolerance at that meal.

Methods: We searched randomized controlled trials published between 1966 and December 2002. Databases in the search strategy included Medline and AMED. We reviewed references of clinical trials and contacted authors of major articles and manufacturers of probiotic commercial products. Quality assessment was based on the McMaster guides and was performed by 5 independent reviewers. Data extraction was performed by 2 reviewers.

Results: A master list of 90 articles was compiled. Ten articles met inclusion and exclusion criteria and were consistent with our clinical question. Of the 9 studies that measured breath hydrogen, 3 were positive, 3 were negative, and 3 had both positive and negative results. Of the 7 studies that measured symptoms, 1 yielded positive results, 5 were negative, and 1 had both positive and negative outcomes.

Conclusions: Probiotic supplementation in general did not alleviate the symptoms and signs of lactose intolerance in adults in this review. Some evidence suggests that specific strains, concentrations, and preparations are effective. Further clinical trials of specific strains and concentrations are necessary to delineate this potential therapeutic relationship.

Practice recommendations
  • Become familiar with the strains, concentrations, and preparations of probiotics most likely to be effective.
  • Because a given individual may respond well to probiotics, suggest a trial of a probiotic supplement—perhaps conducting an n-of-1 trial for an objective assessment.
  • If a trial of probiotic does not achieve desired results, advise the patient of the many other options to treat lactose intolerance.

Judging from our systematic review of the literature, probiotic supplementation is not effective universally for lactose intolerance in adults. However, some evidence suggests that specific strains, concentrations, and preparations of probiotics can be effective.

Discuss probiotic supplementation with lactose-intolerant patients. “Try it” is a reasonable suggestion, given additional evidence that there are individuals whose symptoms of lactose intolerance will, for unknown reasons, respond to probiotics.

For those who find no benefit in probiotics, several other therapeutic options can be recommended.

Prevailing wisdom about lactose intolerance

Lactose intolerant persons suffer such symptoms as abdominal cramping, bloating, and diarrhea after ingesting lactose-containing foods, including nonfermented dairy products.1 This intolerance to dairy products may result in a person receiving less than the recommended intake of calcium and protein, especially in developing countries.

Primary lactase deficiency is the most common form of lactose intolerance.1 In the US, 15% of Caucasians, over 50% of Mexican Americans, and over 80% of African Americans have lactose intolerance.2

Treatment options for lactase deficiency

Lactose-intolerant persons digest yogurt, which is fermented, more easily than milk.2 Nonfermented lactose-containing foods can be consumed in small quantities or with proteins and fats to delay gastric emptying. Nonfermented dairy products are generally tolerated if they are prehydrolyzed to reduce levels of lactose (such as reduced-lactose or lactose-free milk). Finally, synthetic enzyme (lactase) tablets can be taken with lactose-containing dairy foods in an attempt to alleviate symptoms.2

What are probiotics?

Probiotics are live microorganisms that, when ingested, have beneficial effects on the prevention or treatment of disease.3 Some probiotics, such as Lactobacillus, contain β-galactosidase or lactase intracellularly so that ingestion of lactase-containing probiotics might be beneficial for lactose-intolerant individuals, either consumed with food or taken separately as a supplement.

Theoretically, probiotics ingested as supplements would adhere to the intestinal lining and digest dietary lactose, thereby alleviating malabsorptive symptoms from excessive lactose. Probiotics have other positive effects: treating and preventing diarrhea (infectious and antibiotic induced), relieving symptoms of irritable bowel syndrome, alleviating inflammatory bowel disease, and decreasing atopic disease.4,5 The Food and Agriculture Organization of the United Nations and the World Health Organization have reported that there is adequate scientific evidence of the potential for probiotic foods to provide health benefits, and that specific strains are safe for human use.6

Purported advantages of probiotics. Probiotic supplementation may be preferred over lactose-free products due to the inability to monitor and control all dairy products consumed. The varied efficacy of lactase enzymes in different individuals may render probiotics the favored supplement. Also, the option of a natural treatment may appeal to many people.

Testing for lactose intolerance

The hydrogen breath test is the gold standard for diagnosing lactose intolerance. Intestinal bacteria metabolize carbohydrate to generate hydrogen that is rapidly absorbed into the blood perfusing the gut and cleared during a single passage through the lungs.


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