Lactose intolerance and self-reported milk intolerance: relationship with lactose maldigestion and nutrient intake. Lactase Deficiency Study Group

J Am Coll Nutr. 1998 Dec;17(6):631-6. doi: 10.1080/07315724.1998.10718813.


Background: The relationship between lactose-maldigestion, self-reported milk intolerance and gastrointestinal symptoms has not been clearly defined.

Objectives: To evaluate: a) the prevalence of lactose maldigestion and lactose intolerance in a sample of the general population taken from a rural center; b) the frequency of self-reported milk-intolerance and its correlation with lactose-maldigestion; c) the influence of lactose maldigestion, lactose intolerance and self-reported milk intolerance on dietary habits and consumption of total calories, protein, and calcium.

Subjects: We studied a randomized sample of the general population in a small center in Sicily. 323 subjects (150 males, 173 females), age range 5 to 85 years (median 44) were included and underwent H2-breath test after 25 g lactose load. The preliminary dietary investigation spanned 7 consecutive days using a printed dietary form and was under the daily control of a team of dietitians.

Methods: The dietary investigation was completed in the first part of the study and the results were analyzed for nutrient composition by a computerized database. The subjects were then divided into self-reported milk-intolerants and self-reported milk-tolerants and they underwent H2 breath testing; subjects with H2 concentration >20 ppm over the baseline concentration were considered maldigesters and those with one or more symptoms were classified as intolerants.

Results: 104/323 subjects (32.2%) were lactose maldigesters but tolerants, while 13/323 (4%) were lactose maldigesters and intolerants. In each age-class group (pediatric, adult, and elderly subjects) only the lactose maldigester and intolerant subjects showed differences in nutrient intake with a significantly lower daily consumption of milk and a lower calcium intake. 49/323 subjects were self-reported milk-intolerants; of these, 26 (53%) were lactose maldigesters but tolerants, 18 (37%) were lactose digesters and tolerants and only 5 (10%) were lactose maldigesters and intolerants. In the whole group of self-reported milk-intolerants, dietary milk consumption was significantly reduced and calcium intake was lower than in all the other subjects studied (320 mg/day vs. 585 mg/day, p<0.05).

Conclusions: In studies of the general population, the frequency of lactose intolerance is much lower than that of lactose maldigestion. Gastrointestinal symptoms after lactose load in self-reported milk-intolerants are found in only a very low number of these subjects. Furthermore, in these subjects we observed an unnecessary reduction in milk consumption and an insufficient dietary calcium intake.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Adolescent
  • Adult
  • Aged
  • Aged, 80 and over
  • Animals
  • Breath Tests
  • Calcium / administration & dosage
  • Child
  • Child, Preschool
  • Deuterium / analysis
  • Diet
  • Dietary Proteins / administration & dosage
  • Energy Intake
  • Female
  • Humans
  • Lactose Intolerance / diagnosis*
  • Lactose Intolerance / metabolism
  • Male
  • Middle Aged
  • Milk*


  • Dietary Proteins
  • Deuterium
  • Calcium