A COMPARISON OF SYMPTOMS AFTER THE CONSUMPTION OF MILK OR LACTOSE-HYDROLYZED MILK BY PEOPLE WITH SELF-REPORTED SEVERE LACTOSE INTOLERANCE F

Ingestion of a large dose of the milk sugar lactose — for example, the 50-g load in 1 liter of milk — causes symptoms such as abdominal pain, diarrhea, bloating, and flatulence in the majority of people with lactose malabsorption. It is uncertain whether the ingestion of more common doses of lactose, such as the amount in 240 ml (8 oz) of milk, causes symptoms. Some people insist that even smaller quantities of milk, such as the amount used with cereal or coffee, cause severe gastrointestinal distress.  In a randomized, double-blind, crossover trial, we evaluated gastrointestinal symptoms in 30 people (mean age, 29.4 years; range, 18 to 50) who reported severe lactose intolerance and said they consistently had symptoms after ingesting less than 240 ml of milk. The ability to digest lactose was assessed by measuring the subjects’ end-alveolar hydrogen concentration after they ingested 15 g of lactose in 250 ml of water. Subjects then received either 240 ml of lactose-hydrolyzed milk containing 2 percent fat or 240 ml of milk containing 2 percent fat and sweetened with aspartame to approximate the taste of lactose-hydrolyzed milk; each type of milk was administered daily with breakfast for a one-week period. Using a standardized scale, subjects rated the occurrence and severity of bloating, abdominal pain, diarrhea, and flatus and recorded each passage of flatus.  Twenty-one participants were classified as having lactose malabsorption and nine as being able to absorb lactose. During the study periods, gastrointestinal symptoms were minimal (mean symptom-severity scores for bloating, abdominal pain, diarrhea, and flatus between 0.1 and 1.2 [1 indicated trivial symptoms; and 2, mild symptoms]). When the periods were compared, there were no statistically significant differences in the severity of these four gastrointestinal symptoms. For the lactosemalabsorption group, the mean ( SEM) difference in episodes of flatus per day was 2.5 1.1 (95 percent confidence interval, 0.2 to 4.8). Daily dietary records indicated a high degree of compliance, with no additional sources of lactose reported.  People who identify themselves as severely lactose-intolerant may mistakenly attribute a variety of abdominal symptoms to lactose intolerance. When lactose intake is limited to the equivalent of 240 ml of milk or less a day, symptoms are likely to be negligible and the use of lactose-digestive aids unnecessary. ( 1995;333:1-4.) From the Department of Food Science and Nutrition, University of Minnesota, St. Paul (F.L.S., D.A.S.), and the Minneapolis Veterans Affairs Medical Center, Minneapolis (M.D.L.). Address reprint requests to Dr. Levitt at the Minneapolis Veterans Affairs Medical Center, 1 Veterans Dr., Minneapolis, MN 55417. Supported in part by the Department of Veteran Affairs, the National Institute of Diabetes and Digestive and Kidney Diseases (RO1-DK-13093-25), and the University of Minnesota Agricultural Experiment Station. T HE milk sugar lactose must be hydrolyzed by a lactase at the intestinal brush border before it can be absorbed. After weaning, there is a genetically programmed reduction in lactase activity in many people that cannot be altered by the ingestion of milk. 1-3 Such people acquire what has been variously termed “primary acquired lactase deficiency,” “lactase nonpersistence” or “lactose malabsorption.” The ability to maintain throughout adult life the levels of lactase characteristic of infancy is inherited through a single, highly penetrant autosomal dominant gene 4,5 located on chromosome 2. 6 People of northern European descent generally have high lactase levels throughout adulthood. Most other people become lactase-nonpersistent. 5,7 About 25 percent of adults in the United States and 75 percent worldwide have lactose malabsorption. 7,8 Ingestion of a large dose of lactose, such as the 50-g load in 1 liter (1.06 qt) of milk, causes diarrhea, bloating, and flatulence in the majority of people with lactose malabsorption. 9 There is controversy, however, about such people’s tolerance of smaller doses of lactose, such as the amount found in 240 ml (8 oz) of milk. One uncontrolled study suggested that the majority of people with lactose malabsorption have appreciable symptoms after drinking 240 ml of milk. 10 In contrast, a blinded study suggested that most of those with malabsorption tolerate 240 ml of milk without recognizable symptoms. 8 Nevertheless, it is extremely common for patients to insist that ingesting very small quantities of milk, such as the amount used with cereal or coffee, causes severe gastrointestinal distress. This concept of severe intolerance has been nurtured by innumerable articles in the news media and advertisements for lactose-digestive aids. People who believe that they are 2 THE NEW ENGLAND JOURNAL OF MEDICINE July 6, 1995 severely lactose-intolerant have not been adequately represented in previous trials, which have evaluated people with lactose malabsorption independently of whether or not they considered themselves lactoseintolerant. 11-14 In a self-selected group of people with severe lactose intolerance, we evaluated gastrointestinal symptoms after they drank 240 ml of milk daily for one-week periods. Our findings suggest that a variety of abdominal complaints are frequently misattributed to lactose intolerance.