Carbohydrate Intolerance - Gastrointestinal Disorders - MSD Manuals

Enzyme deficiencies can be

• Acquired (primary)

• Secondary

• Congenital

Acquired lactase deficiency (primary adult hypolactasia) leads to lactose malabsorption, which is also called lactose intolerance and is the most common form of carbohydrate intolerance. Lactase levels are high in neonates, permitting digestion of milk. In the majority of the world's population, the levels decrease in the post-weaning period, rendering older children and adults unable to digest significant amounts of lactose. However, certain populations of Northwest European, East African, and Middle Eastern descent, many of whom have historically raised animals for food and milk, produce lactase throughout life and are thus able to digest milk and milk products. This enzyme persistence, termed lactase persistence, is genetically mediated and occurs in the minority of the worldwide population, whereas lactase deficiency is the usual state for most adults worldwide (1–3).

Secondary lactase deficiency occurs in conditions that damage the small-bowel mucosa (eg, celiac disease, tropical sprue, acute intestinal infections [see Gastroenteritis]). In infants, temporary secondary disaccharidase deficiency may complicate enteric infections or abdominal surgery. Recovery from the underlying disease is followed by an increase in activity of the enzyme.

Congenital enzyme deficiencies are rare and include deficiencies of lactase or sucrase-isomaltase.

Etiology references

1. 1. Fernández-Bañares F. Carbohydrate Maldigestion and Intolerance. Nutrients. 2022;14(9):1923. Published 2022 May 4. doi:10.3390/nu14091923

2. 2. Montgomery RK, Krasinski SD, Hirschhorn JN, Grand RJ. Lactose and lactase--who is lactose intolerant and why?. . Lactose and lactase--who is lactose intolerant and why?.J Pediatr Gastroenterol Nutr. 2007;45 Suppl 2:S131-S137. doi:10.1097/MPG.0b013e31812e68f6

3. 3. Swallow DM. Genetics of lactase persistence and lactose intolerance.  . Genetics of lactase persistence and lactose intolerance.Annu Rev Genet. 2003;37:197-219. doi:10.1146/annurev.genet.37.110801.143820