Intolerance of Small Amounts of Lactose by Individuals with Low Lactase Levels

Abstract

Persons with low lactase levels who are aware of milk intolerance report variations in their tolerance of milk ranging from one-half glass to 1 quart. Although low intestinal lactase activity and lactose intolerance as determined by lactose tolerance tests are present in the majority of the world's population, the relevance of tolerance tests using 50 g or 100 g to clinically significant amounts of milk has been questioned. Twenty subjects with assay-confirmed low lactase levels were fed 3 to 96 g of lactose to determine a threshold level for symptoms. Seventy-five per cent of these subjects had symptoms of flatulence, distention, cramps, loose bowel movements, or diarrhea with 12 g of lactose (equivalent to 8 ounces of milk) or less. Two individuals were symptomatic with as little as 3 g of lactose. All 20 subjects were asymptomatic with equivalent amounts of sucrose or a glucose-galactose mixture. Neither the type of symptoms, the specific intestinal lactase levels, nor the presence of the irritable colon syndrome correlated with the threshold level for symptoms. To determine the intraluminal events that occur with small amounts of lactose, 7 low lactase level subjects and 3 control subjects underwent intestinal intubation with aspiration ports in the duodenum, jejunum, and ileum. They were fed 24, 12, 6, or 3 g of lactose with polyethylene glycol, a nonabsorbable marker, in a solution similar to the electrolyte composition of milk. Subjects with low lactase levels had persistently low polyethylene glycol concentrations in the jejunum and ileum, representing fluid accumulation, as compared with control subjects, in whom high concentrations of polyethylene glycol in the jejunum and ileum represented net absorption. Differences from control subjects were statistically significant in the jejunum and ileum (P