Objectives Promotional activities of the infant formula (IF) industry, coupled with insufficient health policy support for breastfeeding, contributes to IF overuse, which may deprive infants of the numerous benefits of human milk and breastfeeding. Within healthcare systems, specialised low-allergy IF is increasingly overprescribed as a remedy for common infant symptoms, despite insufficient evidence.

Biological background assumptions (BBAs) refer to the basic beliefs about the nature of health and contribute to shaping its risk evaluation and research conduct. In case of IF, its safety and effectiveness are often assumed, without sufficient scrutiny. To prevent unnecessary use of IF, it is important to critically examine current BBAs related to IF.

Method After a literature review and using a framework by Rocca and Andersen (2017) we identified the key current BBA: the composition of human milk is sufficiently known and constant over time and across multiple variables, including infants’ gender, developmental stage, geographical location, gestational age, mode of delivery, microbiome, mothers’ age, diet, or mental health. We analysed the following direct consequences of using this BBA:

We critically evaluated these claims based on the framework for weighing complex evidence by Heather Douglas (2012) and proposed a rationale for developing new scientifically plausible BBA with higher explanatory power.

Results The current BBA suffers weaknesses of the qualitative rule-based approach, which prioritizes industry friendly rule stability, but exhibits limited flexibility when the science changes. We applied the superior qualitative explanatory framework to the current BBA: 1. The safety of IF is decided within a regulatory process, which has been shown to be deficient, e.g., safety of many substances added to IF is determined based on animal studies or self-declarations of the manufacturer. 2. There are thousands of unique components in HM, many biologically active. Only very limited number of them is added to IF, sometimes with unclear effects. 3. There is strong evidence that IF increases health risks for infant and mother compared with breastfeeding or donor human milk and there is no scientific consensus on what constitutes optimal infant growth and how it should be measured.

Conclusions Analysis of the current BBA and its consequences in IF revealed poor support by empirical evidence, and an ongoing debate surrounding safety and efficacy of IF. The current BBA critiqued here could (consciously or unconsciously) influence public and health-professional perception of IF and contribute to its overuse as well as overdiagnosis within healthcare systems, where IF is often advised or prescribed for special medical purposes. New scientifically plausible BBAs must acknowledge the evolutionary history of our species: humans are mammals and infant feeding is a complex adaptation shaped by natural selection and contributing to Darwinian fitness. Therefore, HM is a dynamically changing biological system which is unlikely to be optimally artificially reproducible. The mother-infant dyad has co-evolved, further optimizing breastfeeding outcomes. A new set of BBAs grounded in evolutionary thinking would foster a more cautious approach to IF and help prevent its overuse.