Back to Lactose Intolerance and Milk Allergy

Lactose Intolerance

Lactose is the principal carbohydrate in milk. Virtually all mammals are born with high levels of lactase, a unique intestinal enzyme that breaks down lactose, enabling its absorption.1,2

In individuals with lactose maldigestion, any lactose that is not completely digested in the small intestine passes into the large intestine, where it is fermented by colonic microflora that produce gas.2

Lactase deficiency

Primary lactase deficiency is chronic and can begin to develop after weaning. The degree of lactose intolerance depends on a balance between the level of remaining lactase activity, the amount of lactose consumed, the adaptation of intestinal flora and the irritability of the colon.1

Secondary lactase deficiency is temporary. It is a response to gastrointestinal factors (e.g., certain medical conditions, some medications, etc.) that harm the intestinal mucosa. It can occur at any age and is reversible upon correction of the causative factor.1,3 Testing for other underlying conditions (such as Crohn's disease, infectious diarrheal disease and celiac disease) may be necessary.

Diagnosis

Gastrointestinal symptoms are often misdiagnosed as lactose intolerance. The diagnosis can be confirmed by a breath hydrogen analysis, an objective, non-invasive, inexpensive and easy-to-perform test.1

Symptoms of lactose intolerance are highly subjective and may or may not accompany lactose maldigestion.1 Furthermore, there are different types of lactose intolerance reactions, each of which correspond to the degree of intolerance.

Learn more about lactose intolerance reactions ››

Colonic adaptation

According to breath hydrogen tests, newborns are unable to completely hydrolyze the lactose in breast milk. Nevertheless, infant development depends on breast milk and formula, both of which contain lactose.1

Discover the position of pediatricians on lactose intolerance ››

Double-blind crossover studies have been conducted in adults who do not easily digest lactose to determine whether continuous lactose exposure could cause colonic bacteria to metabolize lactose and reduce symptom severity. Gradually increasing lactose intake significantly increased the ability of colonic bacteria to break it down.4 It is clear that the human colon adapts to continued exposure to lactose, which reduces symptoms.1,4-7

Subjects experienced a decrease in breath hydrogen (suggesting that the lactose was being digested) and, concomitantly, a significant reduction in flatulence,4 one of the main symptoms of lactose intolerance. Despite a continued inability to digest lactose (confirmed by breath hydrogen testing), subjects can often tolerate more and more lactose with minimal symptoms.6,7

A 21-day intervention study conducted in 2000 assessed the effects of a dairy-rich diet in 14 African American girls aged 11 to 15 years, all of whom stated they did not drink milk. The study diet contained 4 servings of dairy products providing about 33 g of lactose and 1,200 mg of calcium throughout the day. In addition to a significant decrease in breath hydrogen, gastrointestinal symptoms were negligible during the milk challenges and throughout the study period, no doubt due to colonic adaptation.2 The message is clear: Even individuals who are lactose intolerant can consume milk and milk products. The consumption of milk products remains our best defence against lactose intolerance.

The dose counts

Double-blind, controlled studies have demonstrated that primary lactase deficiency should not be an obstacle to meeting calcium needs with milk and milk products.2,8-10 Lactose intolerance is dose dependent.

Most individuals with primary lactase deficiency—even those who perceive themselves to be severely lactose intolerant—can easily tolerate 1 cup (250 mL) of milk with a meal or 2 cups (500 mL) consumed in divided doses, for example with breakfast and dinner.2,8,9,11 Women with limited lactose digestion can comfortably consume enough milk, yogurt and cheese to provide up to 1,500 mg of calcium/day.10

Interestingly, lactose tolerance appears to increase during pregnancy,12-14 possibly because of slowed intestinal transit.13,14

According to Dr. Denis Savaiano, an expert in lactose intolerance, people can recondition their digestive systems to accept dairy foods without discomfort.15 Smaller quantities, taken with meals or other foods and spread throughout the day, increases lactose tolerance.

Learn more about the myths surrounding lactose intolerance ››

Key messages about lactose intolerance

  • Its prevalence is grossly overestimated;
  • Self-diagnosis is frequently inaccurate;
  • The colon adapts to regular exposure, which increases tolerance;
  • Most lactose intolerant individuals can consume milk products with minimal symptoms;
  • Lactose intolerant individuals who consume milk products have fewer symptoms than those who do not.

References

  1. Miller GD et al. Lactose Intolerance. In: Handbook of Dairy Foods and Nutrition. 2nd ed. Ch. 8:311-354. Boca Raton, Florida: CRC Press, Inc., 2000.
  2. Pribila BA et al. Improved lactose digestion and intolerance among African-American adolescent girls fed a dairy-rich diet. Am J Diet Assoc 2000;100:524-528.
  3. Suarez FL and Savaiano DA. Lactose digestion and tolerance in adult and elderly Asian-Americans. Am J Clin Nutr 1994;59:1021-1024.
  4. Hertzler SR and Savaiano DA. Colonic adaptation to the daily lactose feeding in lactose maldigesters reduces lactose intolerance. Am J Clin Nutr 1996;64:1232-1236.
  5. Hertzler SR et al. Fecal hydrogen production and consumption measurements. Response to daily lactose ingestion by lactose maldigesters. Dig Dis Sci 1997;42:348-353.
  6. Johnson AO et al. Adaptation of lactose maldigesters to continued milk intakes. Am J Clin Nutr 1993;58:879-881.
  7. Briet R et al. Improved clinical tolerance to chronic lactose ingestion in subjects with lactose intolerance: a placebo effect? Gut 1997;41:632-635.
  8. Suarez FL et al. Tolerance to the daily ingestion of two cups of milk by individuals claiming lactose intolerance. Am J Clin Nutr 1997;65:1502-1506.
  9. Suarez FL et al. A comparison of symptoms after the consumption of milk or lactose-hydrolysed milk by people with self-reported severe lactose intolerance. N Engl J Med 1995;333:1-4.
  10. Suarez FL et al. Lactose maldigestion is not an impediment to the intake of 1500 mg calcium daily as dairy products. Am J Clin Nutr 1998;68:1118-1122.
  11. Johnson AO et al. Correlation of maldigestion, lactose intolerance and milk intolerance. Am J Clin Nutr 1993;57:399-401.
  12. Villar J et al. Improved lactose digestion during pregnancy: a case of physiologic adaptation? Obstet Gynecol 1988;71:697.
  13. Szilagyi A et al. Lactose handling by women with lactose malabsorption is improved during pregnancy. Clin Invest Med 1996;19:416.
  14. Paige D et al. Lactose intolerance in pregnant African-American women. J Am Coll Nutr 1997;16(Abstract 69):488.
  15. Savaiano D. Managing lactose intolerance: a food lover’s guide. Presentation. The Smart Gourmet. Dairy Foods for Health and Pleasure. Montréal, Quebec: February 19, 2001.

Keywords: lactose intolerance, health studies

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