The latest (and best) research says that breastmilk or formula is the only food or drink baby needs for 6 months. In saying that, food can be started at 4 months at the earliest.
Reasons to delay introduction until 6 months are that babies have a tongue thrust reflex that should be gone by 6 months allowing them to chew and swallow, introducing before 6 months may lead to constipation or tummy aches due to an immature digestive system and also, unless your baby can sit unsupported (which very few can do at 4 months) there is risk of aspiration and choking on food. Some parents will swear by starting at 4 months because they find baby is too hungry or sleeps better after eating solids, but the research is not conclusive on this.
We started at 6 months with baby cereal and then moved to baby led solids (which is when you don't use purees, rather let baby have a selection of finger foods and allow them to eat at their own pace) and it has worked really well.
Parents are very divided on whether to start at 4 or 6 months, you will hear good arguments for both, so do your own research and follow your own instinct. Your baby will not be harmed by waiting until 6 months, so do not start simply because you think they will not get the nutrition they need. In fact, up to 12 months milk is the MAIN dietary requirement. It is important when you start to approach with caution and if baby is not showing interest or seems to not be able to tolerate a spoon or foods in the mouth, stop and try again another time smile
Solids are fun, but enjoy having the pleasant milk poo nappies as long as possible!
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