Formula is harder to digest than human milk; thus formula-fed babies tend to go longer between feedings. It certainly has a place in infant feeding but probably shouldn’t be used whenever mom’s milk – either directly from the source or expressed – is available. Some babies will sleep worse, due to reactions to the formula or solids (tummy ache, etc. are not uncommon), particularly if baby is younger than around 6 months.
Three studies have indicated that adding solids or formula to the diet does not cause babies to sleep longer. These studies found no difference in the sleep patterns of babies who received solids before bedtime when compared to babies who were not given solids.