What is the gut microbiome and why does it matter

The human body shelters a wide variety of microbial communities (Cong & Zhang, Reference Cong and Zhang2018; Valdes et al., Reference Valdes, Walter, Segal and Spector2018). The gastrointestinal (GI) or gut microbiota is the largest, most diverse, and complex, harbouring billions of bacteria (the predominant organisms), archaea, eukaryotes, and viruses (Ursell et al., Reference Ursell, Haiser, Van Treuren, Garg, Reddivari, Vanamala, Dorrestein, Turnbaugh and Knight2014). The combined gut bacterial communities are referred to as the “gut microbiota,” while the totality of genes that compose the gut microbiota is referred to as the “gut microbiome” (Hou et al., Reference Hou, Wu, Chen, Wang, Zhang, Xiao, Zhu, Koya, Wei, Li and Chen2022). This article refers specifically to the gut microbiome or microbiota, unless otherwise specified. The gut bacteria coexist and interact with the host, helping maintain homeostasis, both locally and systemically. They have a crucial role in food fermentation, pathogen defence, immune stimulation, and vitamin synthesis (Hillman et al., Reference Hillman, Lu, Yao and Nakatsu2017). The composition of the early gut microbiota is typically assessed by analysing infant stool samples using sequencing technologies. The level of taxonomic detail researchers can obtain depends on the specific sequencing method used, with some techniques offering higher resolution than others (Petersen & Round, Reference Petersen and Round2014; Franzosa et al., Reference Franzosa, Hsu, Sirota-Madi, Shafquat, Abu-Ali, Morgan and Huttenhower2015; Young, Reference Young2017; Ruan et al., Reference Ruan, Engevik, Spinler and Versalovic2020; Stinson, Reference Stinson2020).

The initial gut microbiota colonisation starts at birth (Perez-Muñoz et al., Reference Perez-Muñoz, Arrieta, Ramer-Tait and Walter2017). The gut microbiota composition and assembly are highly dynamic during the neonatal period and infancy, stabilising to resemble the adult gut microbiota at 1–3 years of age (Bäckhed et al., Reference Bäckhed, Roswall, Peng, Feng, Jia, Kovatcheva-Datchary, Li, Xia, Xie, Zhong, Khan, Zhang, Li, Xiao, Al-Aama, Zhang, Lee, Kotowska, Colding and Wang2015). Many different factors shape the gut microbiota in early life, including maternal microbiota composition (which, in turn, is greatly influenced by maternal diet), gestational age, mode of birth, antibiotic exposure, genetics, and infant feeding practices (Bäckhed et al., Reference Bäckhed, Roswall, Peng, Feng, Jia, Kovatcheva-Datchary, Li, Xia, Xie, Zhong, Khan, Zhang, Li, Xiao, Al-Aama, Zhang, Lee, Kotowska, Colding and Wang2015; Shao et al., Reference Shao, Forster, Tsaliki, Vervier, Strang, Simpson, Kumar, Stares, Rodger, Brocklehurst, Field and Lawley2019). Delivery mode is the main driver of the initial gut microbiome composition. Babies born vaginally generally show microbiome compositions enriched with microbes of the genera Bifidobacterium, Escherichia, Bacteroides, and Parabacteroides (Bäckhed et al., Reference Bäckhed, Roswall, Peng, Feng, Jia, Kovatcheva-Datchary, Li, Xia, Xie, Zhong, Khan, Zhang, Li, Xiao, Al-Aama, Zhang, Lee, Kotowska, Colding and Wang2015; Shao et al., Reference Shao, Forster, Tsaliki, Vervier, Strang, Simpson, Kumar, Stares, Rodger, Brocklehurst, Field and Lawley2019). Most of the maternal bacterial gut and vaginal microbiota strain transmissions during the neonatal period happened in babies born vaginally, while babies born by caesarean section show more microorganisms from the skin and oral microbiota and the surrounding environment, including potentially pathogenic bacteria such as microbes of the genera Enterococcus, Enterobacter, and Klebsiella (Bäckhed et al., Reference Bäckhed, Roswall, Peng, Feng, Jia, Kovatcheva-Datchary, Li, Xia, Xie, Zhong, Khan, Zhang, Li, Xiao, Al-Aama, Zhang, Lee, Kotowska, Colding and Wang2015; Shao et al., Reference Shao, Forster, Tsaliki, Vervier, Strang, Simpson, Kumar, Stares, Rodger, Brocklehurst, Field and Lawley2019). The differences between delivery modes generally tend to diminish by 6–12 months of age as feeding patterns and solid food introduction become more influential (Bäckhed et al., Reference Bäckhed, Roswall, Peng, Feng, Jia, Kovatcheva-Datchary, Li, Xia, Xie, Zhong, Khan, Zhang, Li, Xiao, Al-Aama, Zhang, Lee, Kotowska, Colding and Wang2015).

There is growing evidence that early gut microbiota composition is associated with later risk of NCDs, such as obesity, asthma, diabetes, and cardiovascular conditions (Sarkar et al., Reference Sarkar, Yoo, Valeria Ozorio Dutra, Morgan and Groer2021). For instance, a longitudinal study found that infants with higher Bifidobacterium levels were more likely to maintain a healthy weight at age 7 years, whereas those with higher Staphylococcus aureus were more likely to become overweight (Kalliomäki et al., Reference Kalliomäki, Collado, Salminen and Isolauri2008). Other studies report inverse associations between Bifidobacterium abundance and markers like glucose intolerance, body mass index, and systemic inflammation (Bjursell et al., Reference Bjursell, Admyre, Göransson, Marley, Smith, Oscarsson and Bohlooly2011; Conterno et al., Reference Conterno, Fava, Viola and Tuohy2011). In animal models, lower ratios of Firmicutes (i.e., Bacillota) (Parks et al., Reference Parks, Chuvochina, Chaumeil, Rinke, Mussig and Hugenholtz2020) to Bacteroidetes and reduced butyrate-producing bacteria have been linked to diabetes development (Siljander et al., Reference Siljander, Honkanen and Knip2019).

Epidemiological studies further highlight associations between early-life exposures and NCDs. Prenatal undernutrition and low birth weight have been associated with higher risks of obesity, cardiovascular disease, and diabetes later in life (Barouki et al., Reference Barouki, Gluckman, Grandjean, Hanson and Heindel2012; Hanson & Gluckman, Reference Hanson and Gluckman2015). Similarly, maternal obesity and gestational diabetes are associated with long-term metabolic risks in both mother and child (Barouki et al., Reference Barouki, Gluckman, Grandjean, Hanson and Heindel2012). Breastfeeding, on the other hand, is consistently associated with lower rates of childhood obesity and adiposity (Ma et al., Reference Ma, Qiao, Zhao, Li, Katzmarzyk, Chaput, Fogelholm, Kuriyan, Lambert, Maher, Maia, Matsudo, Olds, Onywera, Sarmiento, Standage, Tremblay, Tudor-Locke and Hu2020). Despite limitations in the current research, evidence increasingly suggests a link between the early-life gut microbiome and the development of NCDs. This underscores the importance of identifying windows of opportunity for intervention, particularly through diet, one of the most modifiable factors influencing microbiome composition during the first 1,000 days of life. There are three distinct nutritional phases in the first 1,000 days of life in which dietary interventions and exposures can be implemented – (1) the maternal diet in the prenatal period, (2) early infancy when breastmilk is the only required source of nutrition, and (3) the complementary feeding period (Mameli et al., Reference Mameli, Mazzantini and Zuccotti2016). Within each period, numerous factors influence microbial composition (Tamburini et al., Reference Tamburini, Shen, Wu and Clemente2016; Stinson, Reference Stinson2020).

Nutritional factors that affect microbial composition in pregnancy

The importance of nutrition during pregnancy has long been recognised, particularly by the Developmental Origins of Health and Disease Hypothesis, which proposes that in-utero environments influence developmental pathways and future infant health (Chu et al., Reference Chu, Antony, Ma, Prince, Showalter, Moller and Aagaard2016a,Reference Chu, Meyer, Prince and Aagaardb; Stinson, Reference Stinson2020; Maher et al., Reference Maher, O’Brien, Moore, Byrne, Geraghty, Saldova, Murphy, Van Sinderen, Cotter and McAuliffe2023). Despite there being evidence that maternal nutrition in pregnancy affects future health outcomes of the infant, the exact mechanism through which this occurs has thus far remained vague (Brumana et al., Reference Brumana, Arroyo, Schwalbe, Lehtimaki and Hipgrave2017).

Maternal diet can have both positive and negative impacts on the infant’s microbiome. It has been demonstrated that gestational high-fat diets lead to a reduction of Bacteroides in the infant’s microbiome (Chu et al., Reference Chu, Antony, Ma, Prince, Showalter, Moller and Aagaard2016a,Reference Chu, Meyer, Prince and Aagaardb). The reduction in Bacteroides species could impact the development of immunity and energy extraction of some polysaccharides (Chu et al., Reference Chu, Antony, Ma, Prince, Showalter, Moller and Aagaard2016a,Reference Chu, Meyer, Prince and Aagaardb).

Conversely, diets rich in fruits, vegetables, and fibre have been associated with infant microbial compositions lower in unhealthy gut microbes, such as Erysipelatoclostridium, Betaproteobacteria, and Lachnospiraceae (Fan et al., Reference Fan, Tung, Yang, Hsu, Lee, Chang, Su, Hsieh and Chen2021).

Further research is required in this area as significant gaps remain. Many studies fail to account for other variables in this time period, such as delivery mode, thus making it challenging to determine if maternal diet in isolation has a direct impact on infant microbial composition.

Breastfeeding and the developing microbiome

After birth, colonisation of the infant microbiome continues and is highly influenced by human milk consumption, with breastfeeding recognised as one of the most significant factors affecting microbiome development in the first few years of life (Bäckhed et al., Reference Bäckhed, Roswall, Peng, Feng, Jia, Kovatcheva-Datchary, Li, Xia, Xie, Zhong, Khan, Zhang, Li, Xiao, Al-Aama, Zhang, Lee, Kotowska, Colding and Wang2015; Stewart et al., Reference Stewart, Ajami, O’Brien, Hutchinson, Smith, Wong, Ross, Lloyd, Doddapaneni, Metcalf, Muzny, Gibbs, Vatanen, Huttenhower, Xavier, Rewers, Hagopian, Toppari and Ziegler2018; Shao et al., Reference Shao, Forster, Tsaliki, Vervier, Strang, Simpson, Kumar, Stares, Rodger, Brocklehurst, Field and Lawley2019).

Breastfeeding shapes the early gut microbiota composition through different mechanisms. Through direct transfer of microbes, as well as nutrients that stimulate selective bacterial growth, including human milk oligosaccharides or casein glycol-macropeptides (Moossavi et al., Reference Moossavi, Miliku, Sepehri, Khafipour and Azad2018; Boudry et al., Reference Boudry, Charton, Le Huerou-Luron, Ferret-Bernard, Le Gall, Even and Blat2021).

Distinct differences have been identified between the microbiota of exclusively breastfed and exclusively formula-fed infants (Bäckhed et al., Reference Bäckhed, Roswall, Peng, Feng, Jia, Kovatcheva-Datchary, Li, Xia, Xie, Zhong, Khan, Zhang, Li, Xiao, Al-Aama, Zhang, Lee, Kotowska, Colding and Wang2015). Despite the advances in formula milk composition, formula-fed infants still display noticeable microbial features, with an under-representation of Lactobacillus, which leads to an over-representation of other microorganisms such as Clostridium difficile, compared to breastfed infants (Azad et al., Reference Azad, Konya, Maughan, Guttman, Field, Chari, Sears, Becker, Scott and Kozyrskyj2013; Bäckhed et al., Reference Bäckhed, Roswall, Peng, Feng, Jia, Kovatcheva-Datchary, Li, Xia, Xie, Zhong, Khan, Zhang, Li, Xiao, Al-Aama, Zhang, Lee, Kotowska, Colding and Wang2015; Tanaka & Nakayama, Reference Tanaka and Nakayama2017). Breastfed infants also seem to exhibit lower microbial diversity compared to formula-fed infants (Young & Schmidt, Reference Young and Schmidt2008; Azad et al., Reference Azad, Konya, Maughan, Guttman, Field, Chari, Sears, Becker, Scott and Kozyrskyj2013; Davis et al., Reference Davis, Dinsmoor, Wang and Donovan2020).

Complementary feeding

Complementary feeding marks the introduction of semi-solid and solid food into the infant’s diet, when breastmilk or formula milk no longer meets all their nutritional needs (Campoy et al., Reference Campoy, Campos, Cerdo, Dieguez and Garcia-Santos2018). When solid foods are introduced into the diet, a large microbial transition occurs, causing a shift towards a more stable and adult-like microbiome (Laursen et al., Reference Laursen, Andersen, Michaelsen, Mølgaard, Trolle, Bahl and Licht2016). Despite this shift in composition, it is the subsequent cessation of breastfeeding that seems to have a more pronounced effect on microbial development (Bäckhed et al., Reference Bäckhed, Roswall, Peng, Feng, Jia, Kovatcheva-Datchary, Li, Xia, Xie, Zhong, Khan, Zhang, Li, Xiao, Al-Aama, Zhang, Lee, Kotowska, Colding and Wang2015).

In the complementary feeding phase, the microbial composition changes from being mainly characterised by lactobacilli, bifidobacteria, and enterobacteria to microbiota dominated by Clostridium spp. and Bacteroides spp. (Bergström et al., Reference Bergström, Skov, Bahl, Roager, Christensen, Ejlerskov, Mølgaard, Michaelsen and Licht2014). As complementary feeding continues, the differences between the microbiomes of breastfed and formula-fed infants decrease, disappearing by 2–3 years and stabilising to an adult-like phase (Bergström et al., Reference Bergström, Skov, Bahl, Roager, Christensen, Ejlerskov, Mølgaard, Michaelsen and Licht2014; Stinson, Reference Stinson2020).

There is some evidence that early food patterns and dietary habits in the early years of life can affect the gut microbiome composition (Laursen et al., Reference Laursen, Andersen, Michaelsen, Mølgaard, Trolle, Bahl and Licht2016). However, there is a lack of high-quality studies in this phase of development as a result of diet in early childhood being difficult to measure accurately, and there are very few studies exploring the association between specific diets and gut microbiome composition in young children.

Barriers and solutions to healthy eating and breastfeeding can be identified using the social-ecological model

When exploring barriers surrounding nutrition and breastfeeding, it is helpful to break them down using the social-ecological model (SEM). The SEM demonstrates interactions between individuals and their environments, and the influences that shape health behaviours (McLeroy et al., Reference McLeroy, Bibeau, Steckler and Glanz1988).

At an individual level, barriers to a healthy microbiome through diet or breastfeeding include limited knowledge, restricted income, and time constraints (Kavle & Landry, Reference Kavle and Landry2018; Kay et al., Reference Kay, Bentley and Wasser2025). Integrating nutritional education and education on breastfeeding into antenatal appointments can help reduce some of these barriers (Olloqui-Mundet et al., Reference Olloqui-Mundet, Cavia, Alonso-Torre and Carrillo2024).

At an interpersonal level, support from family and friends is key to making positive nutritional choices. Lack of support and detrimental cultural practices can cause significant barriers to healthy eating and breastfeeding (Snyder et al., Reference Snyder, Hulse, Dingman, Cantrell, Hanson and Dinkel2021; Neven et al., Reference Neven, Lake, Williams, O’Reilly, Hendrieckx, Morrison, Dunbar, Speight, Teede and Boyle2022). Mothers who have a supportive partner are more likely to breastfeed, as well as women who have family members who have breastfed (Lok et al., Reference Lok, Bai and Tarrant2017; Gebrekidan et al., Reference Gebrekidan, Fooladi, Plummer and Hall2020).

At a community level, systemic issues lead to barriers. In rural areas, difficult access to fresh food can force individuals to opt for highly processed, unhealthy options (Whelan et al., Reference Whelan, Millar, Bell, Russell, Grainger, Allender and Love2018). Without adequate support and sufficient infrastructure, it is hard for families to make healthy nutritional choices. Community-based support groups, positive social norms, and urban gardens can all help promote healthy behaviours and breastfeeding (Shakya et al., Reference Shakya, Kunieda, Koyama, Rai, Miyaguchi, Dhakal, Sandy, Sunguya and Jimba2017; Garcia et al., Reference Garcia, Ribeiro, Germani and Bógus2018).

At the policy level, the absence of robust legislation and public health initiatives causes significant barriers. Lack of legislation, or enforcement of legislation, regulating corporate actors in the formula milk industry has had detrimental effects on breastfeeding rates globally (Baker et al., Reference Baker, Russ, Kang, Santos, Neves, Smith, Kingston, Mialon, Lawrence, Wood, Moodie, Clark, Sievert, Boatwright and McCoy2021; Lutter et al., Reference Lutter, Hernández-Cordero, Grummer-Strawn, Lara-Mejía and Lozada-Tequeanes2022). Alongside this, policies designed to protect and encourage breastfeeding are lacking, including failure to ensure adequate maternity leave, separating infants and mothers at birth, and failure to address stigma associated with breastfeeding in public (Rollins et al., Reference Rollins, Bhandari, Hajeebhoy, Horton, Lutter, Martines, Piwoz, Richter and Victora2016; Grant et al., Reference Grant, Pell, Copeland, Brown, Ellis, Morris, Williams and Phillips2022). Healthy food is often unaffordable. Although some governments have imposed taxes on high-sugar foods, very few have introduced subsidies to make nutritious foods more accessible (Blakely et al., Reference Blakely, Cleghorn, Mizdrak, Waterlander, Nghiem, Swinburn, Wilson and Ni Mhurchu2020).

While individual choices influence dietary decisions and breastfeeding, the SEM demonstrates that these behaviours are shaped by interpersonal, community, and policy-level factors. Solutions to these barriers can be found at every level, but often the most impactful and lasting solutions come from a policy level. Recognising this shifts the narrative that places full responsibility for healthy choices on individuals and allows for a more equitable approach to public health.

To boost microbial development at the population level, we must do more to protect, promote, and support breastfeeding

One of the most effective ways to increase healthy microbial development is breastfeeding (Stewart et al., Reference Stewart, Ajami, O’Brien, Hutchinson, Smith, Wong, Ross, Lloyd, Doddapaneni, Metcalf, Muzny, Gibbs, Vatanen, Huttenhower, Xavier, Rewers, Hagopian, Toppari and Ziegler2018). There are many well-known health benefits associated with breastfeeding, including a lowered risk of infectious morbidity and mortality in children and a reduced risk of breast cancer in mothers (Victora et al., Reference Victora, Bahl, Barros, França, Horton, Krasevec, Murch, Sankar, Walker and Rollins2016). Despite this knowledge, breastfeeding rates are low in many parts of the world (UNICEF Data, 2018). In LMICs, 1 in 25 infants are never breastfed, but in HICs this rises to 1 in 5 children not receiving any breastmilk at all (UNICEF Data, 2018).

The determinants of breastfeeding are complex and multifactorial, ranging from social and cultural attitudes, unsupportive environments, and the commercial interests of the formula milk industry (Rollins et al., Reference Rollins, Bhandari, Hajeebhoy, Horton, Lutter, Martines, Piwoz, Richter and Victora2016).

Many commercial products are known for increasing the risk of developing NCDs, but the goods involved are highly profitable for companies and highly convenient for consumers (Horton et al., Reference Horton, Perman-Howe, Angus, Bishop, Bogdanovica, Brennan, Britton, Brose, Brown, Collin, Dockrell, Fitzgerald, Friel, Gillespie, Gilmore, Hill, Knai, Langley, Martin, McNeill, Moore, Munafò, Murray, Opazo Breton, Pearce, Petticrew, Reid, Robson, Rutter, Shahab, Shortt, Smith, Syrett and Bauld2021). The breastmilk substitute industry is no exception to this. It is estimated to be worth US$70 billion (van Tulleken et al., Reference van Tulleken, Wright, Brown, McCoy and Costello2020). Commercial marketing of formula milk negatively impacts breastfeeding rates (Rollins et al., Reference Rollins, Bhandari, Hajeebhoy, Horton, Lutter, Martines, Piwoz, Richter and Victora2016). Despite legislation published by the World Health Organization (WHO) attempting to outlaw advertising and promotion of formula milk, consumption of breastmilk substitutes remains widespread in HICs and is rising rapidly in the rest of the world, while some countries, including the United States, have not adopted the legislation into national guidelines (Soldavini & Taillie, Reference Soldavini and Taillie2017; Hastings et al., Reference Hastings, Angus, Eadie and Hunt2020).

Alongside commercial marketing, barriers to breastfeeding are also seen within healthcare systems and workplaces (Tomori, Reference Tomori2022). An important barrier to address is the environment created in hospitals to successfully initiate and establish breastfeeding. Early initiation and exclusive breastfeeding are often key to successful breastfeeding in line with public health recommendations, and require the mother and child to be within continuous reach of each other (Tomori, Reference Tomori2022). The Baby Friendly Hospital Initiative, based on the Ten Steps for Successful Breastfeeding, was created by the WHO in conjunction with the United Nations Children’s Fund (UNICEF) to try and improve breastfeeding rates and duration in hospitals (Fallon et al., Reference Fallon, Harrold and Chisholm2019). This guidance educates healthcare staff and parents about breastfeeding and ensures mothers and infants are able to remain together within the hospital environment (WHO & UNICEF, 2009).

As the post-partum period continues, more barriers to breastfeeding become apparent. It has been found that paid maternity leave is a key determinant of breastfeeding. Maternity leave encourages both breastfeeding initiation and duration (Lauzon-Guillain et al., Reference Lauzon-Guillain, Thierry, Bois, Bournez, Davisse-Paturet, Dufourg, Kersuzan, Ksiazek, Nicklaus, Vicaire, Wagner, Lioret and Charles2019).

To improve breastfeeding rates, support and intervention will be required at many levels – from personal and social influences to legal and political legislation that promotes and enables breastfeeding (Rollins et al., Reference Rollins, Bhandari, Hajeebhoy, Horton, Lutter, Martines, Piwoz, Richter and Victora2016).

If we believe that breastfeeding is important for microbial development, then globally, the current state of low breastfeeding rates will be a barrier to leveraging its potential to address NCDs through the pathway of microbial development, as will the commercial interests in the sphere of infant and young child feeding.

The healthy diet and “breast is best” rhetoric places too much emphasis on individual choice

The wider discourse that nutritional decisions in the first 1,000 days are solely dictated by women’s individual choice and preference needs to be challenged.

There are many determinants surrounding food choice, including environmental, cultural, familial, and genetic factors (Leng et al., Reference Leng, Adan, Belot, Brunstrom, de Graaf, Dickson, Hare, Maier, Menzies, Preissl, Reisch, Rogers and Smeets2017). Global and national policymaking often overlooks many of these determinants. Little regard is paid to socio-economic factors, despite the evidence showing that higher quality diets are generally consumed by people of a higher economic status and lower quality diets tend to be consumed by less affluent populations (Darmon & Drewnowski, Reference Darmon and Drewnowski2008).

Oversimplification of the “healthy eating” rhetoric that places all responsibility on individual choice and ignores the social determinants of health has thus far failed to stem the rising burden of NCDs (Kriznik et al., Reference Kriznik, Kinmonth, Ling and Kelly2018). Instead, a more integrated approach that considers structural barriers alongside the social and commercial determinants of health must be applied.

We must also examine the pressure and responsibility that is placed on women and mothers to provide good-quality infant nutrition and exclusively breastfeed for 6 months. We live in a world that sexualises and stigmatises women’s bodies while simultaneously shaming them for not breastfeeding. When women are unable or choose not to breastfeed, there is often a narrative of blame, which further places responsibility on the individual woman rather than examining the structural, social, and political barriers that may have contributed to the outcome (Tomori, Reference Tomori2022).

Symbiotic products – another silver bullet that misses the mark?

Like most global public health nutrition issues, the discourse on healthy microbial development in the first 1,000 days displays a predilection for fast fixes. “Silver bullet” solutions, such as pro- and prebiotics, claim to be the key to a healthy microbiome. The symbiotic industry, which includes probiotics and prebiotics products, is estimated to be a multi-billion-dollar market (Quin et al., Reference Quin, Estaki, Vollman, Barnett, Gill and Gibson2018). While consumers generally view these products as beneficial for their health, there is often a lack of knowledge on how the products work, and evidence on safety and efficacy is patchy (Cunningham et al., Reference Cunningham, Azcarate-Peril, Barnard, Benoit, Grimaldi, Guyonnet, Holscher, Hunter, Manurung, Obis, Petrova, Steinert, Swanson, van Sinderen, Vulevic and Gibson2021). These issues come as a consequence of the symbiotic industry being largely unregulated and governance varying between different regions and countries (de Simone, Reference de Simone2019). There have been relatively few studies that evaluate the use of symbiotic products for developing and maintaining the early microbiome. Among the few studies that have been done, the results are varied, and many call for further studies into the long-term effects and safety of these products (Quin et al., Reference Quin, Estaki, Vollman, Barnett, Gill and Gibson2018; Westaway et al., Reference Westaway, Huerlimann, Kandasamy, Miller, Norton, Watson, Infante-Vilamil and Rudd2022).

While these commercial symbiotic products might have some benefits for the microbiome, they do not match the additional benefits that breastfeeding and healthy diets confer in ways unrelated to the microbiome. The pathways linking breastfeeding and healthy eating to lower NCD risk can thus be split into two – one mediated by microbial development and a separate pathway encapsulating all other benefits related to social, psychological, emotional, physiological, and nutritional processes. The impact of symbiotics on NCDs will, therefore, be smaller than the total effects of the more holistic benefits of breastfeeding and healthy diets. If breastfeeding and healthy diets can do the same job as symbiotics and much more besides, why not develop interventions, policies, and support for these instead of hoping that yet another silver bullet in the form of symbiotics will solve a global public health crisis?