Formula Tolerance in Postbreastfed and Exclusively Formula-fed Infants

Perceived intolerance to infant formula is a frequently reported reason for formula switching. Formula intolerance may be related to perceived symptoms of constipation, fussiness, abdominal cramps, and excessive spit-up or vomit. Commercially available formulas differ from each other in processing and in sources and levels of protein, lipids, and micronutrients. These differences may affect tolerance. The objective of this article was to compare the tolerance of two commercially available powder infant formulas that differ in composition. Measures of tolerance in exclusively breastfed infants weaned to an infant formula and exclusively formula-fed infants were evaluated. Two clinical studies were conducted. In study 1, 82 healthy, full-term infants who were exclusively breastfed at the time of enrollment were randomized at weaning to formula A (commercially available Similac With Iron Powder) or formula B (previously available Enfamil With Iron Powder). Parents completed daily records of tolerance during exclusive breast milk feeding, during the weaning period, and for a 2-week exclusive formula-feeding period. In study 2, 87 healthy, full-term infants who were exclusively formula-fed at the time of study enrollment (by 2 weeks of age) were fed a standard cow milk-based formula (previously commercially available Similac With Iron Powder) and then randomized to receive formula A or B for a 2-week period. Parents completed daily records of tolerance throughout the study. Formula A was a cow milk-based formula with a whey:casein ratio of 48:52 and a fat blend of 42% high-oleic safflower, 30% coconut, and 28% soy oils. Formula B was a cow milk-based formula with a whey:casein ratio of 60:40 and a fat blend of 45% palm olein, 20% soy, 20% coconut, and 15% high-oleic sunflower oils. Both formulas had lactose as the source of carbohydrate and contained 12 mg of iron per liter. Only formula A contained nucleotides at the time of the study. Measures of tolerance included volume of each formula feeding, occurrences of spit-up and/or vomit, and the color (yellow, green, brown, or black) and consistency (water, loose/mushy, soft, formed, or hard) of each stool. In both studies, volume of formula intake, weight gain, and incidence of spit-up or vomit did not differ between feeding groups. In study 1, stool frequency decreased significantly from the exclusive breast milk period to weaning. Stools also became firmer as infants moved from breast milk to weaning and to exc