Parenthood is a state that expecting parents rarely experience with a sense of complete readiness, often accompanied by the anxiety of providing the best for their future child. This naturally extends to optimal practices for feeding the child, particularly in their early stages. The present guidelines from the World Health Organization (WHO) regarding infant feeding advocate for exclusive breastfeeding during the initial 6 months, followed by the introduction of complementary foods while sustaining breastfeeding for 2 years or more [1]. As an alternative to breast milk, infant formula (IF) is specifically designed for babies under one year old. While the advantages of breastfeeding are well-known, an increasing number of parents are choosing to transition to IF [2,3]. The perception that supplementation with IF is necessary often arises in response to unsettled infant behaviors, such as persistent crying [4]. This belief is influenced, in part, by marketing claims suggesting that IF can yield positive outcomes for infants’ behavior, immunity, and growth, among other factors [2]. However, these marketing practices can also contribute to uncertainty surrounding the use of IF [2].

With exclusive breastfeeding rates falling below 50% in most countries [3], our objective is to delve into the scientific aspects of breast milk and its potential impact on infant well-being. Responding to a reader’s request, we will initially clarify the similarities and differences between the composition of breast milk and IF. Subsequently, we will provide a concise overview of some of the ongoing studies that explore health outcomes associated with these two feeding options.

Both breastmilk and IF aim to provide the necessary nutrients that an infant needs. The most common component of IF is cow milk, although milk of other mammals or soy-based alternatives are also available [5]. They generally consist of a mix of macro and micronutrients, such as carbohydrates, proteins, lipids and vitamins/minerals [6]. In the US, at least 30 distinct nutrients are mandated to be included in IF by the FDA to emulate the composition of nutrients in human breastmilk [7]. On top of nutritional content, different bioactive compounds can also be found in some IF, such as probiotics and folates, present also in human milk [8]. Regulated IF can provide an infant with adequate nutrition and is the only suitable alternative to replace or supplement breastmilk whenever breastfeeding is not possible. However, there are still some key differences between breastmilk and IF, including the composition of distinct sugars and non-nutritional factors unique to breastmilk that can affect infants’ short and long term well-being [9,10]. Current IFs lack quintessential factors present in breastmilk, such as hormones, a diversity of microbes, maternal antibodies and immune cells [10,11]. These factors not only affect infant growth via its appetite and sleep, but also shape early-life immune responses against diseases and the gut microbiome [4,5,11–13]. For example, breastfed infants have distinct microbiomes shaped by a combination of the microbiota, immune cells and types of sugars only found in human milk [3,14,15]. Furthermore, breast milk serves as a dynamic medium through which communication between parent and child influences its composition—an adaptability that is crucially lacking in IF. For instance, the nutritional content of breast milk may vary among individuals, feeding episodes, and infant development [16]. Overall, breast milk encompasses several factors that contribute to infant health, elements absent in IF. The translation of these factors into short or long-term effects on infants will be explored in the following paragraphs.

Currently, meta-analyses of pooled studies support the benefits of breastfeeding against other alternatives, including IF, even after considering confounding factors. Breastfed infants up to 2 years of age are more likely to survive irrespective of the economic status of the country [3,16]. Notably, research indicates that breastfeeding can provide protection against infectious diseases, diarrhea, and acute otitis media, though it does not show a similar protective effect against eczema, food allergies, or asthma [3]. Concerning potential long-term effects, there is evidence supporting a reduced risk of obesity and diabetes in individuals who were breastfed [3]. Additionally, engaging in direct breastfeeding with skin-to-skin contact has been linked to lower rates of asthma and obesity compared to feeding breast milk with a spoon, bottle, or cup [4]. Consequently, while both infant formula and breast milk may generally be considered safe for infant consumption, breastfeeding offers a broader spectrum of potential health benefits for the child.

However, several challenges hinder the implementation of optimal breastfeeding practices, manifesting as various socio-economic barriers, including insufficient education, workplace policies, and maternal benefits, among others [4]. In such circumstances, infant formula gains a notable advantage over breast milk – particularly in terms of convenience and the maternal benefits it offers for daily routines [18]. At an individual level, nearly half of mothers worldwide transition to IF prematurely, citing self-reported insufficient milk [4]. In such cases, IF may serve as a supplementary solution to meet the infant’s nutritional needs when necessary.

It is evident that IF is still unable to fully emulate breast milk for the advantageous outcomes of direct breastfeeding for infants in their infants early months (< 6 months). IF should not be considered as a complete substitute for breastmilk unless recommended by a professional. Infant health benefits marketed by IF manufacturers are often poorly backed and can lead to confusion [19]. Recognizing the significant advantages of breastfeeding, there is a recent advocacy for comprehensive interventions at the societal level to address the decline in breastfeeding rates [1,3,4]. Importantly, the responsibility to enhance breastfeeding practices should not solely rest on mothers but should be complemented by a supportive environment that ensures the best possible outcomes for infants.