Effects of Ultra-Processed Foods Consumption in Gut Microbiota in the First Two Years of Life: A Systematic Review

The first years of life are a critical period for the development of the gut microbiota. The intake of ultra-processed foods (UPF) is increasing worldwide, even among infants. This systematic review summarizes the available evidence on the relationship between UPF consumption and gut microbiota during the first 2 years of life (PROSPERO CRD42025106520). Exclusion criteria were the absence of gut microbiota data as an outcome or UPF as an exposure; children with comorbidities or older than 2 years; in vitro or animal studies; and review papers. Literature searches were conducted on May 12, 2025, in PubMed, LILACS, Scopus, and Web of Science. The risk of bias was assessed using the Newcastle-Ottawa Scale for cohort and case-control studies, the Joanna Briggs Institute Critical Appraisal Tool for cross-sectional and randomized trials, and the Risk of Bias in Non-randomized Studies of Interventions (ROBINS-I) tool for non-randomized studies. Of the 2,212 records identified (1,520 after duplicate removal), 72 full texts were reviewed, and seven studies were included: six were observational (five cohort and one cross-sectional), and one was a randomized trial. Three studies evaluated the relationship between UPF intake and gut microbiota alpha diversity, but only one showed significant effects. Six studies assessed taxonomic associations: three reported decreased Bifidobacterium abundance, and three found increased Blautia. The evidence was limited by a moderate risk of bias, small sample sizes, and inconsistent diversity findings. Nevertheless, early-life UPF intake was linked to taxonomic changes, suggesting the potential for adverse effects on the gut microbiota.