This is a myth, there is no evidence to suggest that formula milk fills up a baby more than breast milk. What formula feeding enables a parent to see is how much milk your baby has taken at a feed. And at an evening or night feed, this would give a good indication of when your baby should wake next due to actual hunger. Having the confidence to know that your baby is waking due to habit or simply coming in and out of a sleep cycle (instead of second guessing hunger) can be helpful when addressing sleep issues.
Ways to make breastfeeding more effective for little ones' sleep include making sure baby is not "snacking" and is taking a full feed at each feed to ensure they will not wake more frequently. And making sure to stop the feed if baby begins to nuzzle or play so that we teach them that feeding is for sustenance rather than something to use to fall asleep with.
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