The rhythm of hunger and fullness

The conversation

Feeding is a conversation between your baby's stomach and their brain, and it runs on hormones and signals rather than on a clock.

It goes round in four beats. The stomach sends out hunger hormones, and your baby starts giving you clues. You offer a feed. As the stomach fills and the nutrients arrive, the full signals go up, and your baby slows down or turns away. Then the body gets on with digesting, and the conversation starts again when it's ready for more.

A brand-new digestive system

Your baby's digestive system is new and still learning, and it works differently from yours. That explains a good deal of the common grumbles.

The valve at the top of the stomach is loose and uncoordinated, which is the main reason for effortless spit-up. The stomach itself is small and still working out how to produce digestive juices, so breaking down milk takes real effort. And the intestines are short and move things along quickly, which means gas and some memorable diapers.

Colostrum is built for exactly that. Low in volume and high in energy, antibodies and nutrients, matched to what a newborn can actually digest, and delivering a lot in a very small amount.

That tank expands fast, though. A one-month-old can take considerably more at a feed than a newborn could, which is why feeds gradually get bigger and further apart.

What hunger looks like before the crying

Crying is a late sign of hunger, like a final alarm. Before it, your baby sends a whole sentence of quieter signals.

The whisper comes first: smacking lips, sucking on hands, turning the head. That's "I might be getting peckish."

Then the polite ask: rooting, which is turning towards a touch on the cheek with the mouth open. There's squirming too, and a focused sort of alertness. That's "I'm ready to eat."

Then the loud call, which is fussing, crying and turning red.

And when they've had enough, they slow down, turn their head away, their hands relax, and often they fall asleep.

How they know they're full

Two checks run while your baby eats. Receptors in the stomach wall feel it gently expanding, and as the milk digests the body registers the nutrients arriving. When both messages reach the brain together, that's the feeling of being full.

Which is why a faster-flow bottle doesn't get a baby fuller faster.

The rhythm across a day, and across months

Feeding also helps set the body clock. Daytime feeds want to be bright, social and engaging. Night feeds want to be dark, calm and boring. That contrast is a good part of what teaches a body that day is for activity and night is for sleep.

Evening cluster feeding sits between the two, and it looks alarming the first time it happens. It's more like filling the tank before a long drive.

The whole rhythm changes as they grow:

Feeding, sleep, and your part in it

Feeding and sleep pull on each other in both directions. Enough in the day means fewer wakings from hunger. And a well-rested baby feeds better. An overtired one is fussy and distracted, and tends to snack rather than take a full feed, which comes back around as a worse night.