Manufacturers state that the composition of infant formula is designed to be roughly based on a human mother's milk at approximately one to three months postpartum; however, there are significant differences in the nutrient content of these products.[2] The most commonly used infant formulas contain purified cow's milk whey and casein as a protein source, a blend of vegetable oils as a fat source, lactose as a carbohydrate source, a vitamin-mineral mix, and other ingredients depending on the manufacturer.[3] In addition, there are infant formulas using soybean as a protein source in place of cow's milk (mostly in the United States and Great Britain) and formulas using protein hydrolysed into its component amino acids for infants who are allergic to other proteins. An upswing in breastfeeding in many countries has been accompanied by a deferment in the average age of introduction of baby foods (including cow's milk), resulting in both increased breastfeeding and increased use of infant formula between the ages of 3- and 12-months.[4][5]