During your baby’s first year there will be a time when you will have to start to wean her onto solid foods, although not before she’s four months, and possibly quite a bit later that that. Before this, your baby’s digestive tract is incapable of digesting and absorbing complex foods.
Breast milk (or its formula equivalent) is the only food that your baby needs in the early months, and if a baby is introduced to solids too young it can lesson her desire to suck. Breastfed babies will take less milk from your breasts, and you will respond by producing less milk. Either way your baby will end up having an unsatisfactory diet for her needs.