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Amidst Additives: Ultra-Processed Foods Harm Infant Gut

    An illustration of a woman breastfeeding her child with a two-tone background of junk food or ultra-processed foods (UPFs) on the left, and healthy foods on the right.

    Written by: Brittany T. Truong, Ph.D. | Issue # 127 | 2025

    • Ultra-processed foods (UPFs), such as bags of chips or boxes of cookies, are common in most diets; they’re delicious, convenient, and addictive.
    • In adults, the overconsumption of UPFs is associated with significant health problems, including disruptions to the gut microbiome; however, it was unclear how it affects young children.
    • A new longitudinal study that followed infants from birth through their first year suggests that consuming UPFs has a negative impact on the diversity and abundance of intestinal microbes in the infant gut. 
    • Breastfeeding seems to have a protective effect on the infants by promoting the growth of Bifidobacterium, a sign of a healthy infant gut. 

    When you walk into a grocery store, you’re likely to find rows and rows of brightly colored ultra-processed foods (UPFs), including chips, cookies, instant noodles, candy, energy drinks, cereal—the list is endless. 

    The NOVA Food Classification System, developed by the Center for Epidemiological Studies in Health and Nutrition, School of Public Health at the University of São Paulo in Brazil, classifies UPFs as items that have undergone significant modifications. They are made from substances extracted or derived from other foods and contain many additives.  

    UPFs are delicious, addictive, affordable, and convenient, but they’re also associated with significant health problems. 

    Studies have shown that an increased consumption of UPFs in adults is linked to higher risks of all-cause mortality, cardiovascular disease-related mortality, obesity, type II diabetes, and adverse mental health [1, 2]. There is also growing evidence that UPFs may disrupt the gut microbiome in adults by reducing the overall diversity and promoting a proinflammatory environment, which can lead to gut diseases, such as inflammatory bowel syndrome or colorectal cancer [3].

    Until now, it was unclear how UPFs impact infant health, particularly the gut microbiome. Colonization of the gut during infancy is essential for the development of the digestive and immune systems [4], and given the ubiquitous and harmful nature of UPFs, this was a notable knowledge gap in the field. 

    A new study published in Clinical Nutrition by researchers at the University of São Paolo in Brazil have found that the consumption of UPFs has a negative impact on the diversity and abundance of intestinal gut microbes in infants; however, breastfeeding appears to have a protective effect [5]. 

    The study included 728 infants from the Maternal and Child Health and Nutrition in Acre, Brazil (MINA–Brazil), a population-based birth cohort that sought to understand the effects of the environment and maternal choices on the development of children in the Amazon [6]. 

    The researchers collected data on breastfeeding and complementary feeding during follow-up visits at 1 month, 6 months, and 1 year after childbirth. At the 1-year visit, parents were asked to provide a detailed account of what the infant ate the day before. They used the NOVA Food Classification System to help determine which foods were UPFs. The researchers used these data to divide the infants into four groups: breastfed with no UPFs; breastfed with UPFs; weaned with no UPFs; and weaned with UPFs. More than 85% percent of infants consumed UPFs at least once a day, and almost 70% were breastfed [5]. 

    The researchers also collected fecal samples at the 1-year visit. They extracted bacterial DNA from the feces, performed 16S ribosomal RNA sequencing to identify and quantify the bacteria, and calculated the diversity within each group (alpha) and between groups (beta) [5]. 

    They found that infants who consumed UPFs had a greater diversity of bacteria in the gut microbiome than infants who did not [5]. This was expected, given that the infants were eating different types of food aside from milk. The researchers also noted that their guts had a higher abundance of the phylum Firmicutes, which indicates these infants’ gut microbiomes are maturing [7].

    Weaned infants who ate UPFs also had a greater abundance of harmful genera, such as Sellimonas and Finegoldia, than the breastfed group [5]. Previous studies have associated Sellimonas with obesity and precocious puberty in children [8] and depressive symptoms in adults [9]. Moreover, certain species of Finegoldia are considered to be opportunistic pathogens [10]. 

    Breastfed infants, regardless of whether they consumed UPFs, had higher levels of Bifidobacterium than infants who had been weaned, which is a sign of a healthy gut. Bifidobacterium are beneficial for the development of the immune system and may defend infants from antibiotic-resistant bacteria. The authors hypothesized that the Bifidobacterium may have a protective effect on the infant gut microbiome by promoting a stable environment [5]. 

    The researchers note that there were several limitations to this study. For example, they did not include infant formula in their analyses, even though it is classified as a UPF, and breastfed and formula-fed infants have distinct gut microbiomes [11]. They also did not quantify the amount of UPFs the infants ate each day, which could have influenced their results [5].

    To date, this is the largest longitudinal study to analyze the effects of UPFs on the infant gut microbiome [5]. Together, these data suggest that UPFs have a negative effect on the infant gut, while breastfeeding may attenuate them [5]. The research adds to the growing body of literature that supports limiting UPF consumption, regardless of age, and encouraging breastfeeding when possible. 

     

    References

    1. Lane MM, Gamage E, Du S, Ashtree DN, McGuinness AJ, Gauci S, et al. Ultra-processed food exposure and adverse health outcomes: Umbrella review of epidemiological meta-analyses. BMJ. 2024 Feb 28;384:e077310.
    2. Fang Z, Rossato SL, Hang D, Khandpur N, Wang K, Lo CH, et al. Association of ultra-processed food consumption with all cause and cause specific mortality: Population based cohort study. BMJ. 2024 May 8;385:e078476.
    3. Rondinella D, Raoul PC, Valeriani E, Venturini I, Cintoni M, Severino A, et al. The detrimental impact of ultra-processed foods on the human gut microbiome and gut barrier. Nutrients. 2025;17(5):859.
    4. Wernroth M-L, Peura S, Hedman AM, Hetty S, Vicenzi S, Kennedy B, et al. Development of gut microbiota during the first 2 years of life. Sci Rep. 2022 2022/05/31;12(1):9080.
    5. Faggiani LD, de Franca P, Seabra SG, Sabino EC, Qi L, Cardoso MA. Effect of ultra-processed food consumption on the gut microbiota in the first year of life: Findings from the MINA-Brazil birth cohort study. Clin Nutr. 2025 Mar;46:181-90.
    6. Cardoso MA, Matijasevich A, Malta MB, Lourenco BH, Gimeno SGA, Ferreira MU, et al. Cohort profile: The maternal and child health and nutrition in acre, Brazil, birth cohort study (MINA-Brazil). BMJ Open. 2020 Feb 17;10(2):e034513.
    7. Palmer C, Bik EM, DiGiulio DB, Relman DA, Brown PO. Development of the human infant intestinal microbiota. PLOS Biology. 2007;5(7):e177.
    8. Wang L, Yi Q, Xu H, Liu H, Tan B, Deng H, et al. Alterations in the gut microbiota community are associated with childhood obesity and precocious puberty. BMC Microbiology. 2024 2024/08/24/;24.
    9. Radjabzadeh D, Bosch JA, Uitterlinden AG, Zwinderman AH, Ikram MA, van Meurs JBJ, et al. Gut microbiome-wide association study of depressive symptoms. Nature Communications. 2022 2022/12/06;13(1):7128.
    10. Boyanova L, Markovska R, Mitov I. Virulence arsenal of the most pathogenic species among the gram-positive anaerobic cocci, finegoldia magna. Anaerobe. 2016 Dec;42:145-51.
    11. Ma J, Li Z, Zhang W, Zhang C, Zhang Y, Mei H, et al. Comparison of gut microbiota in exclusively breast-fed and formula-fed babies: A study of 91 term infants. Sci Rep. 2020 2020/09/25;10(1):15792.