Starting solids is a big step for your baby -- he’s learning a whole new way of eating, after all! All those new foods affect his every aspect of his digestion, including what ends up in his diapers. That’s right -- we’re talking poop today! Starting Solids? The Poop Changes! Before you start your baby on solid foods, it’s best to prepare yourself in advance for the fact that starting solids will probably affect your baby’s poop. The poop will smell worse. The poop may be brightly colored.