Why do newborns need to suckle so much when their tummy is so little?

Newborns expect a lot of suckling at the breast during the first days (and nights) of life

From an evolutionary perspective, a newborn expects a great deal of suckling at her mother's breast in the first days of life.

It doesn't seem to be hunger that makes your newborn cry for the breast in the first two or three days of life - it's the need for sensory motor nourishment, the need to be up close to your body, drinking in the wonderful, wrap-around sensory motor experience of suckling at your breast. It is difficult to separate out a baby's need for physical contact and the sensory motor experience of suckling from the baby's need for milk. From an evolutionary perspective, these two elements can't be separated, as (in best possible circumstances) the sensory motor drive will also meet the infant's caloric needs.

Newborns don't need a lot of milk in the first days after birth

Your exclusively breastfed baby might take no more than one to five millilitres of breastmilk each time she suckles at the breast in the first day or two of her life. Despite the very small amounts of milk transferred early on, which is completely normal, your baby needs the opportunity to suckle at your breast very frequently from that very first day if you possibly can, to establish your best possible milk supply down the track.

The newborn stomach might be surprisingly small in size - but this is not relevant to the baby's caloric needs

Some health professionals illustrate that it's not the need for milk which primarily drives suckling at first, by offering comparative estimates of the size of a newborn's stomach. These estimates are inaccurate. You might have seen charts with these estimates, but they are not science-based, and might be misleading. For example, neonatologist Dr Nils Bergman has calculated in a 2013 publication that the size of a newborn stomach is more like 20 mls in capacity.

Newborn age	Item similar in size to the newborn's stomach
Day 1	Cherry
Day 2	Walnut
Day 7	Apricot
Day 28	Hen's egg

This misunderstands the many factors that contribute to a mother and baby's biological system in the first days after birth, which has been designed, from an evolutionary point of view, to ensure adequate caloric intake. It also misunderstands the many factors which might disrupt this, and which we need to be alert to in our baby's first days of life.

Stomach size is highly variable from birth. The stomach is designed to stretch. Stomach size does not determine a baby's needs for milk - the baby's metabolism does.

Fed is best content on stomach size here.