How do infant formulas compare to composition or performance of human milk?

During the first year of life, the optimal form of nutrition delivery to infants is through breastfeeding, according to a chapter of “Infant Formula: Evaluating the Safety of New Ingredients,” published on the National Library of Medicine website. According to the chapter titled “Comparing Infant Formulas with Human Milk,” breastfeeding is endorsed by several health agencies, including the World Health Organization, the American Academy of Pediatrics, the American Academy of Family Physicians, the American Dietetic Association, the Institute of Medicine, the Life Sciences Research Organization, the US Department of Health and Human Services, Health Canada, and the Canadian Paediatric Society.

In the United States, by the time infants are 6 months of age, most are fed human milk substitutes. In multiple ways, these substitutes are not ideal compared to human milk, but do promote “more efficient growth, development, and nutrient balance than commercially available cow milk,” according to the book. In attempts to imitate the make-up or performance of human milk, manufacturers will frequently add new ingredients to their respective infant formulas. Additional ingredients present risks resulting from bioavailability, toxicity possibility, and the “practice of feeding formula and human milk within the same feeding or on the same day.”

Adding new ingredients to infant formulas “is usually driven by the manufacturer’s desire to produce a product that mimics the advantages of breastfeeding,” the book states. Developing human milk substitutes is not a new aspect of feeding infants, as according to the book, “it was clear that cow milk was most likely the best animal-milk base to work from.” Safety modifications were made for human infants, such as the removal of animal fat and vegetable oil substitution and adding or balancing vitamins, among others. These modifications have continued ever since. In 1959, iron was added to reduce iron deficiency risk in infants that are fed formula, while “fatty acids were recently added in an effort to improve infant visual and cognitive development.”

Manufacturers of infant formulas make changes to formulas “to match either human milk composition or breastfeeding performance. In attempts to match human-milk composition, companies will add new ingredients. Since human milk is a complex fluid that varies not only by individuals but within an individual over time, mimicking it can be a tall task.

According to the text, “Manufacturers who wish to add some, but not all, ingredients found in human milk may defeat the purpose of the added nutrients or may potentiate negative interactions.” The context of how nutrients are provided in human milk vs infant formula remains an issue for manufacturers. For example, ratios of the same nutrients found in both milks could be different in each. Related to long-chain polyunsaturated fatty acids (LC-PUFAs), “Manufacturers must study the effects of fats, minerals, enzymes, or other factors on LC–PUFA bioavailability and processing.” According to an example in the book, fat absorption in newborns can be highly variable due to the immaturity of lipases, such as pancreatic lipase. Since human milk contains lipases that make up for the lacking pancreatic lipases, human-milk fat is more “bioavailable than the vegetable oils found in infant formulas,” the book states.

Matching breastfeeding performance can also drive infant formula manufacturers to add new ingredients. The initial goal of formulas was to match the growth rate of the breastfed infant, but as time went on, it was recognized that several potential benefits were associated with breastfeeding. These benefits are not necessarily all attributed to the nutritional make up of human milk, as there are advantages related to the interaction between the infant and her mother. According to the book, “It has been difficult to sort out which of the performance factors of breastfeeding are due to nutritional components and which are accounted for by social and psychological factors.” For ethical reasons, trials cannot randomly assign infants to breastfeed or formula.

Breastfed infants, according to the text, grow at different rates and may have a reduced risk for obesity later in life. These infants absorb fat better than infants who are fed formula because of the presence of lipases found in human milk and not in cow milk. Less milk is consumed by a healthy breastfed infant “(approximately 85 kcal/kg body weight/day) during the first months of life than the same infant given ad libitum infant formula (100 kcal/kg/day; Heinig et al., 1993),” according to the book. Further, the breastfed infant takes in approximately 10 less kcal/kg/body weight calories compared to an infant fed with formula, and has a “lower total energy expenditure and a slower growth rate.”

Breastfeeding does come with potential risks, of which the best documented are iron and vitamin D deficiencies, and exposure to environmental toxins. In breastfed infants, iron deficiency is approximately twice as common, as “up to 30 percent have iron deficiency anemia, and more than 60 percent of the anemic infants are also iron deficient at 12 months of age.” Compared to supplemented cow milk formula, the iron content of human milk is low (0.5 mg/L vs 10-12 mg/L). Vitamin D is lacking in human milk, with average concentrations of 24 to 68 IU/L. Breastfed infants consume less than 0.5 L of milk per day during the initial months of life, but with exposure to the sun the intake is not likely to be a problem. “However, infants born to mothers with vitamin D deficiency are at increased risk for rickets, as are those who are not exposed to the sun. The American Academy of Pediatrics and the Canadian Paediatric Society recently recommended supplementing all breastfed infants with 200 IU of vitamin D by 2 months of age.”

Overall, the chapter “Comparing Infant Formulas with Human Milk” from “Infant Formula: Evaluating the Safety of New Ingredients” affirms breastfeeding “is the standard by which all other infant-feeding methods should be judged.” Comparing potential formulas with human milk to evaluate the safety of new ingredients results in research and regulatory issues. Clinical studies aimed at evaluating the effects of new formula ingredients cannot randomize infants to consume formulas or milk. If efforts mimic the advantages of breastfeeding, it is implied that formula is inferior to breastfeeding, resulting in new ingredients. As a result, according to the book, “the safety (and efficacy) of any addition of an ingredient new to infant formulas will need to be judged against two control groups: one fed the previous iteration of the formula without the added ingredient, and one breastfed.”

This article was published by our sister publication Contemporary Pediatrics.

Reference:

Institute of Medicine (US) Committee on the Evaluation of the Addition of Ingredients New to Infant Formula. Infant Formula: Evaluating the Safety of New Ingredients. Washington (DC): National Academies Press (US); 2004. 3, Comparing Infant Formulas with Human Milk. Available from: https://www.ncbi.nlm.nih.gov/books/NBK215837/