The science of breastfeeding: time for a change?

Breastfeeding has always been a matter of considerable interest in medicine, and a great number of studies have been carried out to evaluate its effects. Yet not all of them seem to be equally relevant. Solid scientific evidence has incontrovertibly demonstrated the superiority of breastfeeding for infant nutrition over every other possible surrogate, not only for biological and nutritional outcomes, but also from a psychological and relational point of view. The list of potentially beneficial components of human milk is extensive: it contains growth factors, immunoglobulins, cytokines, antimicrobial compounds as well as factors promoting intestinal colonization by favourable microbes (1). Nevertheless, the list of its alleged beneficial effects has also grown disproportionately, brought on by a panoply of scientific or not-so-scientific studies that have ridden the wave of breastfeeding science and eventually made breastfeeding a panacea, with presumed effects even very distant in time from infancy. Some of these claims are probably even beyond the possibility of a demonstration. And after many years of enthusiastic support, some of them are beginning to undergo a process of critical revision and sometimes have been even disproved. Take the example of obesity. Searching on Pubmed for ‘breastfeeding AND obesity’ returns more than 1000 results with a steep increase in their number in the last 10 years. The Agency for Healthcare Research and Quality ‘Report on maternal and infant health outcomes in developed countries’ by Ip et al. (2), after examining a great amount of published data, concluded that there was ‘an association between a history of breastfeeding and a reduction in the risk of being overweight or obese in adolescence and adult life’. The next sentence was possibly overlooked: ‘One should be cautious in interpreting all these associations because of the possibility of residual confounding’. Furthermore, even the World Health Organization (WHO) systematic review and meta-analysis report on the long-term effects of breastfeeding, while also concluding for a protective effect on obesity, had found clear evidence of publication bias in the published literature (3). More recent studies have questioned the possibility of a protective effect on obesity. A randomized, controlled trial involving more than 13 000 children who were followed for more than 11 years did not find substantial evidence of a protective effect of breastfeeding on obesity (4). Even if this issue may still be considered open, we may ask ourselves: do we really need a more certain answer? We do not think so. If we focus our attention on the advantages of breastfeeding in infancy, we can see that they are generally clear cut and quite easy to demonstrate. Breastfeeding has been shown to be able to reduce morbidity and mortality in infancy, mainly decreasing the incidence of infectious diseases (2,3). It has been calculated that exclusive breastfeeding for 6 months and weaning after 1 year in developing countries could prevent 13% of the world’s childhood mortality (5). In preterms, it stimulates gastrointestinal growth and maturity, reducing the riskof sepsis andnecrotizing enterocolitis (6). In consideration of all the available evidences, the superiority of breastfeeding in infant nutrition canbealready considered an establishedmatter of fact, evenwithout looking for its remote effects on adult health. This is not even surprising if we think that human milk composition has been finely tuned for human nutrition by thousands years of evolutionary pressures. In this sense, its superiority may be considered to be a Articles in the series A Different View are edited by William Meadow (wlm1@uchicago.edu). We encourage you to offer your own different view either in response to A Different View you do not fully agree with, or on an unrelated topic. Send your article to Dr. Meadow (wlm1@uchicago.edu).