What changes when my baby starts formula?

How do I know if she's accepted it?

That was the question after the first Kendamil feed, and then again, more insistently: is there really no way to know after one feed?

No. And that's genuinely the answer rather than an evasion.

An immediate allergic reaction would show within minutes to an hour — a rash, swelling, breathing changes, forceful vomiting. That you would see. But tolerance, in the ordinary sense of whether it suits her, shows over days rather than at the first bottle.

What usually changes

Nappies, most obviously. Firmer, darker, often less frequent. That's the biggest visible difference and it has its own guide, because the gaps can get long enough to be alarming.

More gas for a week or two while her gut adjusts. It generally settles.

Often longer between feeds — we asked whether formula keeps a baby full for longer, and it does tend to, because it's digested more slowly.

And some spitting up while she gets used to it, which usually calms down.

She spat up milk with foam in it and we wanted to know what that meant.

Usually it's air mixed into the milk — from a fast feed, from shaking the bottle vigorously, or from swallowing air while feeding. Letting a made-up bottle stand for a minute so the bubbles settle helps, and so does slowing the feed down.

On its own, with a comfortable baby who's gaining, it isn't something to act on.

Give it a fortnight

The instinct when a formula seems not to suit is to try another one. We felt it strongly.

But each switch resets the adjustment period, so a run of changes produces a permanently unsettled baby and no information at all. Two weeks on one formula tells you far more than four days each on three.

The exceptions are the allergy signs — rash, swelling, breathing changes, blood in the nappy, forceful vomiting. Those don't get a fortnight. Those get a phone call.