When changing formulas, we usually suggest switching directly over to the new formula, but your doctor is in the best position to guide you. A change in a baby's diet often requires an adjustment period that may result in slight changes in his or her digestive process. These changes could include stool pattern change, gas, and/or spitting up. Most babies adapt to their new diet within 3-5 days. Your baby's doctor is in the best position to answer your questions about any symptoms your baby may be experiencing.