When to stop feeding your baby lactose

Sometimes the lingering effects of a stomach bug can make it hard for little ones to digest lactose.

By Jodi Di Menna

Last winter, Clare Tansey and her partner, parents to a then-11-month-old baby boy named Thomas, had a very rough couple of weeks. “It was one of those months when you feel like you’ve been through a war,” says Tansey.

It started when Thomas developed croup (and its signature barking cough), then a double-whammy gastro and respiratory flu that resulted in a high fever, a febrile seizure and a weekend in the children’s hospital, including 48 hours of intravenous antibiotics.

“Through the whole thing he had awful diarrhea,” Tansey recalls. “We kept thinking, ‘Oh, it’s because of the medicine, or it’s because of the flu.’ But it just kept going on and on.” To make matters worse, the diarrhea brought on a painful, bleeding diaper rash that made Thomas tremble and cry with each trip to the change table. After six weeks, a simple suggestion from their paediatrician finally brought relief: Take the lactose out of his diet. Just 24 hours after the couple changed their son’s formula to one that was lactose-free, and removed all other dairy from his meals, he was having solid bowel movements.

“We nearly framed the diaper, we were so jubilant,” Tansey jokes. The problem, it turns out, was a temporary intolerance to lactose, probably caused by one of Thomas’ viruses. After his several weeks of illness and the slew of medicines he’d been prescribed, the doctors determined that Thomas’ gut just needed a rest from dairy, says Tansey.

This kind of “secondary” intolerance to lactose can happen in young children after an “injury to the gut,” says Sarah Schwartz, a paediatrician at the Hospital for Sick Children in Toronto. An injury, she explains, could be an acute stomach flu (gastroenteritis), a bout of persistent diarrhea or a parasitic infection. That’s because these kinds of injuries can damage the cells in the lining of the small intestine that produce lactase, the enzyme that breaks down lactose into sugars that can be absorbed effectively by the body. (Lactose is the main carbohydrate in all mammalian milk, including breastmilk.) When there’s not enough lactase being produced, the lactose in milk products doesn’t get broken down and just passes right through the digestive system. This is what creates all the symptoms of lactose intolerance: diarrhea, abdominal pain, flatulence, bloating and nausea. If these symptoms persist after a child has otherwise recovered from a stomach bug, it could just be that his lactase production has suffered a setback and needs some time to recover, says Schwartz.


In rare cases, such as children with very significant symptoms (like Thomas), or for infants younger than three months, short-term elimination of lactose-containing products may be required. According to Schwartz, it’s difficult to say how prevalent this condition is, because many kids don’t experience symptoms, despite having a gut injury. (In most cases, kids whose lactase production has taken a hit after a stomach bug will still produce enough of the enzyme to digest the amount of dairy in their diet.) Even though this wasn’t Tansey’s experience, Schwartz assures parents that the intolerance almost always resolves itself on its own within a few days. Be patient, and continue to provide nutritious, balanced meals. “Lactase activity should return after a short period,” she says. “With time, most kids will recover just fine.”

A version of this story appeared in our June 2013 issue with the headline "Gut feeling," p. 76.

This article was originally published on May 30, 2013

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