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Ingestion of a large, single dose of lactose by lactose maldigesters commonly results in diarrhea, bloating, and flatulence. However, multiple factors affect the ability of lactose to induce perceptible symptoms. These factors include residual lactase activity, gastrointestinal transit time, lactose consumed with other foods, lactose load, and colonic fermentation. This chapter reviews the pathophysiology of lactose maldigestion, attempts to correct common misconceptions concerning the frequency and severity of lactose intolerance symptoms, and provides dietary strategies to minimize symptoms of intolerance. In addition to food sources of lactose, small amounts of lactose are found in a wide variety of medications due to the excellent tablet-forming properties of lactose. Avoidance of milk and milk products is unnecessary since moderate lactose consumption does not produce a symptomatic response in maldigesters. Additionally, various dietary strategies effectively manage lactose intolerance by reducing or eliminating gastrointestinal symptoms. Dairy food consumption is possible for individuals who are lactose intolerant if simple dietary management strategies are incorporated into daily living.

To determine whether African-American adolescent girls who were fed a dairy-rich diet for 21 days could adapt to lactose, experiencing an overall improvement in lactose tolerance as well as a decrease in hydrogen gas production.Twenty-one-day dietary intervention study.Seventeen of 21 African-American girls (aged 11 to 15 years) enrolled in a calcium metabolism study chose to participate in the lactose tolerance study. Subjects were screened for any diseases, conditions, or medications that might alter calcium metabolism or colonic fermentation. Subjects were housed in a fraternity on the Purdue University, West Lafayette, Ind, campus, and were supervised 24 hours a day.Subjects consumed a dairy-based diet averaging 1,200 mg calcium and 33 g lactose per day for 21 days. Lactose digestion was assessed by an 8-hour breath hydrogen test on days 1 and 21, and symptoms of intolerance (abdominal pain, bloating, flatulence, and diarrhea) were evaluated hourly on a ranked scale during the breath hydrogen tests and once each evening during the 21-day feeding period.A comparison of breath hydrogen production and gastrointestinal symptoms at the beginning and end of the study.The Wilcoxon signed ranks test was used to compare the area under the curve for the 2 breath hydrogen tests. Spearman's p test for trend was used to determine whether there was a change in symptoms. All statistical analyses were 2-tailed and significance was set at P = .05.Fourteen of the 17 subjects had lactose maldigestion. Breath hydrogen excretion decreased significantly (P.03) from the beginning (148.3 +/- 27.0 ppm x hours) to the end (100.7 +/- 19.3 ppm x hours) of the 21-day period. Gastrointestinal symptoms were negligible during both the breath hydrogen tests as were symptoms during the 21-day period.The diet was well tolerated by the subjects. Furthermore, the decrease in breath hydrogen suggests colonic adaptation to the high-lactose diet. The results indicate that lactose maldigestion should not be a restricting factor in developing adequate calcium diets for this population. The existence of lactose maldigestion does not result in lactose intolerance in this population when it is fed a dairy-rich diet.