Research has shown that soft stools are common in children fed either whey- or casein-predominant formulas. However, pediatric nutrition research has reported more children receiving whey-predominant formulas passing softer or more watery stools than did children receiving casein-predominant formulas.1 This could be the result of whey-predominant formulas helping to produce a stool bacteria population similar to that of a breast-fed child and/or due to the fact that whey proteins move more quickly through the stomach than casein.2,3
1 Malacaman EE, Abbousy FK, Crooke D, Nauyok G. Effects of protein source and iron content of infant formula on stool characteristics. Journal of Pediatric Gastroenterology and Nutrition. 1985; 4:771-773.
2 Rochat F, Cherbut C, Barclay D, et al. A whey-predominant formula induces fecal microbiota similar to that found in breast-fed infants. Nutrition Research. 2007; 27:735-740.
3 Balmer SE, Scott PH, Wharton BA. Diet and faecal flora in the newborn: casein and whey proteins. Archives of Disease in Childhood. 1990; 64:1678-1684.