Although some people say this helps their baby sleep longer, there are many other factors that make them wake up, and it might not work at all. Feeding unnecessary foods may even make things worse.
The detailed answer:
This is a common misconception. Parents are often tempted to try formula (or introduce food early) when the dreaded “4 month sleep regression” hits, in an attempt to help their child to sleep more. In fact, formula and solids are both harder to digest than breastmilk, so have the potential to cause sleep to be worse.
We also need to remember, of course, that babies can wake for a range of reasons, hunger being only one of them, so even if you were able to stop them being hungry throughout the night, they still may wake for many other reasons.
In addition, creating a situation in which a baby does sleep for longer and deeper stretches, can actually be a SIDS risk in itself, so is best to be avoided.
If breastfeeding is going well and you find yourself thinking of introducing formula just to try to get more sleep, you may prefer to try other things instead. Keep up the breastfeeding as it will be really useful way to get them back to sleep through teething and other things later. It probably isn’t worth trying formula at this stage if breastfeeding is going well (and if you are breastfeeding a younger baby, you may be interested in the virgin gut theory about how it can affect their gut health).
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