How feeding changes behaviour can be seen soon after the birth...
As and when a baby cries, mother thinks baby is hungry and she feeds him/her.
Consequences he pukes more, produces more gas and always remains fussy.
Baby passes more stool resulting in more rashes over his bumps that further hurt him more.
He never learns to soothe himself and his pain threshold goes down and confuses himself between hunger and transitions into alert state. All babies do cry, they cry for hunger, they cry for wet diaper or cry for pain but most cry for no reason.
All suck their hands and fingers to busy them as they have only few expressions.
Their digestive system is already in developing state, and gets overwhelmed easily with unscheduled feeding...