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Is a Baby Lactose Intolerant?

Concerned woman holds crying baby in striped onesie in bright room.

How many times have you heard this? I’ve heard this, many times. “Stop breastfeeding. This baby is lactose intolerant.” Really? Um, not so fast. Most of us realize that true lactose intolerance is unlikely to affect a “baby.” A child? Maybe. But it’s still highly unlikely. Let’s check the facts related to lactose intolerance.

Is there more than one type of lactose intolerance?

Yes. There are really two main types of lactose intolerance. Congenital (“true”) lactose intolerance, and transient (secondary) lactose intolerance.

What is true lactose intolerance?

True lactose intolerance is a congenital condition. It’s the inability to break down lactose. Meaning, it’s an autosomal recessive trait where the needed enzyme (lactase) is absent, and therefore lactose (the sugary component) cannot be broken down.

True lactose intolerance is very rare. Why so? Because like any autosomal condition, both the mother and the father must pass on the defective form of the gene for the offspring to be affected.

Think about it. How many people do you know who have this congenital condition, and how many of them have a child with each other? Not many, right?

Think about it a little more. If this condition was common, the baby would not be able to tolerate the mother’s milk, and the human species would have died out before the days when lactose-free formula was invented, right?

Some common sense tells us that this condition isn’t common. Period.

But such a diagnosis is possible, right?

Yes, absolutely. It certainly can be possible.

When does true lactose intolerance show up?

Although the deficiency of the enzyme is present at birth, the signs and symptoms are not apparent until several weeks after birth. 

In adults, lactose intolerance occurs gradually when their bodies gradually produce a decrease in lactase. The signs and symptoms usually occur during adulthood and almost never before age 4 or 5.

What happens if a baby has true lactose intolerance?

The congenital condition is present at birth, but it may take a few weeks for signs and symptoms to appear. Typically, this includes:

  • Gastrointestinal signs and symptoms, including discomfort
  • Losing weight
  • Failure to thrive

What can be done to help infants who have true lactose intolerance?

Remember, this is a congenital condition. More specifically, it’s an inborn error of carbohydrate metabolism. And, like any other congenital condition, this condition isn’t reversible. Lactose-free formula can help these infants.

If it’s not true lactose intolerance, could it be something else?

Yes. It it’s not terribly uncommon for babies to have transient lactose intolerance, often called secondary lactose intolerance.

Why would “transient lactose” intolerance occur?

As the term “secondary” implies, it occurs secondary to an event. Usually, diarrhea.

The underlying cause of transient lactose intolerance is injury to the gastrointestinal mucosa that happens during a severe episode of diarrhea.

Can the baby continue to breastfeed with transient lactose intolerance?

Yes. The American Academy of Pediatrics and the Centers for Disease Control recommend continuing breastfeeding during these episodes. In extreme cases, the baby might also need some oral rehydration therapy to avoid dehydration.

What happens if they have transient lactose intolerance?

Although similar to congenital or true lactose intolerance, the signs and symptoms of transient lactose intolerance are episodic, and less severe. These include:

  • Diarrhea
  • Bloating
  • Gassiness
  • General gastrointestinal discomfort

What can be done to help infants who have transient lactose intolerance?

Multiple published peer-reviewed studies have shown this: Discontinuing breastfeeding during a diarrheal illness increases risk of an infant becoming sicker.

Treatment management for transient lactose intolerance is beyond the scope of what I can address here. But to my knowledge, there’s no evidence to support discontinuation of breastfeeding during these episodes.

Anything else that’s important to know?

Yes. Like all my posts, this is post is for information and education only. It is not intended for diagnosis or treatment. I’m not a licensed dietitian or physician, so I’m not giving advice. 

That said, I encourage readers NOT to stop breastfeeding for a presumed lactose intolerant condition without seeking further testing and expert management by a fully qualified pediatric gastroenterologist, dietitian, and/or other qualified experts.

Is there another lactose condition?

Yes! And it’s relatively common. It’s called lactose overload. Many breastfed babies experience lactose overload at one time or another.

 Lactose IntoleranceTransient Lactose IntoleranceLactose Overload
Underlying causeLack of enzyme lactaseDiarrhea followed by injured GI mucosa; resolves as GI mucosa healsMore-than-normal consumption of lactose; resolves when there is less lactose to deal with
Onset of symptomsA few days after birthAfter episode of diarrheaMany days after birth when infants get too much lactose.
IncidenceRare, rare, rareCommonCommon

Stay tuned, I’ll address lactose overload in a separate post!

How often have you heard of a newborn as being “lactose intolerant”?

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