Lactose intolerance in babies

It happens in my office all the time. A mother declares that her infant is lactose intolerant: “Everyone in my family is”.

The professional in me keeps a neutral facial expression while I internally groan. And since the doctor has marked that the infant should receive Similac Sensitive for Fussiness and Gas, helpfully providing an additional diagnosis of “lactose intolerance”, I issue the infant checks for the lactose-free formula.

I groan because lactose intolerance in babies is incredibly rare. Babies’ guts make the lactase enzyme so they can break down the lactose found in their mother’s milk (all mammals’ milk includes lactose). It is only as children grow older and less dependent on mothers’ milk that their bodies stop producing the enzyme to process it.

The few exceptions are 1) primary lactase deficiency, which rarely ever occurs, 2) secondary lactase deficiency, where a gastrointestinal illness temporarily wipes out the body’s ability to make lactase, and 3) prematurity, where an infant is born before her gut lining has started to produce lactase.

Which brings me to my biggest groan.

Tirzah Mae had only ever received my breastmilk, slowly increasing feedings as the IV nutrition was decreased. Most of what she got was via the feeding tube, but she’d started taking it by bottle in the last few days – and we’d started practicing breastfeeding once a day as well.

As I prepared myself for our breastfeeding practice, I noticed that Tirzah Mae had spit up – and I mentioned it to the nurse, who observed that the spit up was bright yellow (my color discrimination has been poor since I delivered, so I didn’t notice anything odd about it under the dim lights.) When the nurse checked the residuals left in Tirzah Mae’s stomach, they were green. Feedings were put on hold and breastfeeding practice suspended.

That evening, the nurse practitioner came in to discuss the situation. She explained the plan: to start again with smaller feedings and work our way up again – and asked me how much dairy I consumed.

She explained how preemies sometimes don’t yet have the ability to process lactose and requested that I reduce my intake of dairy down to maybe one serving a day – and maybe I could try lactose-free milk instead of regular.

I put on my patient face, inquiring about what she thinks might help, while inwardly groaning.

You see, despite the opinions of plenty of doctors and nurses, lactose intake by a woman actually has no impact on the amount of lactose present in her milk.

In a lactose-tolerant woman, any lactose she eats is broken down into its component sugars in her gut, from which the component sugars are absorbed into her blood stream. Then, independently, her breasts take sugars from her blood stream and synthesize them into lactose for her breastmilk.

In a lactose-intolerant woman, any lactose she eats passes through her gut into her colon unabsorbed – and bacteria in her gut ferment it, producing the typical symptoms of lactose intolerance (gas, diarrhea, abdominal cramping, etc.) Then, independently, the mother’s breasts take sugars from her blood stream and synthesize them into lactose for her breastmilk.

It’s simple science, really. But doctors and nurses didn’t spend their educations studying the science of digestion and absorption and metabolism like dietitians do.

So they give silly, unscientific advice related to diet and mothers swear by it because they see improvement when the prematurity (or the GI illness) that caused the problem in the first place resolves (sort of like thinking the antibiotic cured your child’s cold when it resolves in 7-10 days)**.

I choose not to argue and dutifully consume just one serving of dairy daily (actually, I only ever consumed one serving of lactose-containing dairy daily – since my former pattern was one cup of milk, one cup of yogurt, and one serving of hard cheese daily). I label my breastmilk “low dairy” and dream of the day when I can go back to eating whatever I want to without being dishonest. (Since the only reason I’m not eating the dairy now is so I wouldn’t be dishonest in writing “low dairy” on my breastmilk – I already know the restriction isn’t affecting her at all.)

**Caveat: Some women who are told that their infant has lactose intolerance and who reduce dairy as a result discover that this truly is helpful (and symptoms resume when milk is reintroduced). This is generally a case of mistaken identity. While lactose in mom’s intake and lactose in breastmilk are not related, the more cow’s milk a mother consumes, the more cow’s milk proteins will end up in her milk – and some babies do have sensitivities to cow’s milk proteins, which would resolve when mom reduces dairy intake.**