Is My Baby Lactose Intolerant, Sucrose Intolerant, or Both?

Is My Baby Lactose Intolerant, Sucrose Intolerant, or Both?

Diarrhea in babies is not an uncommon complaint at the pediatrician’s office. Physicians turn frequently to the possibility of lactose intolerance as the cause; and in the majority of cases with formula-fed babies experiencing diarrhea or fussiness, pediatricians will suggest a change to a lactose-free formula, usually with poor results.

Primary lactase deficiency, or congenital lactose intolerance – not to be confused with a milk protein allergy, is an extremely rare condition; and a majority of cases in newborns and young infants are in Finland. There are only a few hundred babies with this condition in the world.

Babies with primary lactase deficiency usually develop severe diarrhea within hours of ingesting breastmilk, which is loaded with lactose, or regular infant formula. These babies will become very sick and dehydrated unless lactose is withdrawn from their diet.

Congenital sucrose intolerance, albeit still not common, occurs much more frequently than primary lactase deficiency and is prevalent across different ethnicities. These babies usually do well with breastmilk or lactose-containing formulas; but when they are exposed to fruit or vegetables at around five months, they develop diarrhea, bloating, and fussiness.

Initially these babies are thought to be dealing with a viral process, but eventually the connection between sucrose-containing food and symptoms is made, and they are diagnosed with Congenital Sucrase-Isomaltase Deficiency (CSID).

The only instance where using lactose-reduced formulas may make sense is if a baby develops diarrhea for another cause, for example rotavirus; and they develop flattening of their intestinal villi leading to secondary sugar enzyme deficiencies. That means that babies can be lactose and sucrose intolerant for a couple of weeks until they re-grow their intestinal lining. These conditions are called secondary lactose and sucrose intolerances and resolve themselves once the underlying disease or condition is resolved.

In summary, both lactose and sucrose intolerances can present with diarrhea and gassiness in young infants, but we should remember that primary lactase deficiency is very rare in the United States. Practitioners and parents should keep in mind that congenital sucrose deficiency is much more common, especially when babies develop diarrhea with the introduction of solids such as fruits and vegetables in their diets. Diarrhea usually resolves with elimination of these sugars in their diet for two weeks.

I hope that this helps clarify the differences between primary lactase deficiency, congenital sucrose intolerance, and secondary or acquired lactose and sucrose intolerances.

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Sucrose Intolerance May Be More Common Than You Think