This is one of THE BEST formulas on the market because it is closer to the composition of breastmilk. Good Start is 100% whey proteins (which is what makes it so easily digestible) and contains probiotics, which most of the others do not. You will notice less spitting up and easier bowel movements using this formula. Give it a couple of weeks for your baby's digestive system to adjust. There is a difference in taste so you might try a slow transition making 3 parts of your current formula to one part Good Start and then slowly add more each day or feeding. Dirty diapers may more closely resemble those of breast-fed babies as well, more greener, pastier, and seedy - this is normal. This is definitely a great formula with infants who spit-up a lot or have acid reflux. I would try this one first before using one of the more expensive brands such as Nutramigen, Allimentum, etc. These have such a bitter taste!