How to Read the Literature
Composition of Human Milk How to Read the Literature

The volume of breastfeeding literature has grown exponentially in recent years. Conducting studies on the health effects of breastfeeding is challenging, in part because it is not ethical to randomize subjects to a non-breastfeeding group, due to the documented health risks associated with not breastfeeding. There can also be biases in research questions, or potential conflict of interests on the part of the investigators, particularly if there are ties to the pharmaceutical, formula, for-profit milk banking, or infant feeding industries. In evaluating a study, notice who sponsored the study and how the authors categorized breastfeeding groups.

Most benefits of breastfeeding demonstrate a dose-response gradient, meaning that the greater the proportion of breastmilk in the infant’s diet, the greater the difference in health outcomes between infants who are breastfed as compared to infants not breastfed.

It is important that studies use the accepted standard definitions for breastfeeding. The exclusively breastfed infant receives only breastmilk at the breast – no formula, water, teas, or porridges. The exclusively breastmilk-fed infant may receive milk from a cup, bottle, or other vessel, as well as at the breast. A partially breastfed infant receives some other substance besides breastmilk – yet many studies categorize these infants as “breastfed.” The ever breastfed infant may only have gone to breast one time in the hospital or perhaps stopped breastfeeding once at home.

Studies that do not distinguish between these groups or are vague in defining breastfeeding will have questionably valid results.