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inflammation (4,12,13). Targeting gut microbiotacomposition through dietary interventions can beconsidered a therapy option for reversing dysbiosis inpatients with OB caused by diet.1.2. Obesity and overweight in pediatricpopulationsOB is derived from a positive energy imbalancebetween energy consumed and energy expendedmaintained over time. It is a disease characterized byexcessive fat accumulation and a low -grade chronicinflammation that presents a risk to health (14).Globally there has been an increase in the intake ofhigh-energy-dense foods that are high in sugars andfats, and a decrease in physical activity (15).Since pediatric populations are continuously growingit is difficult to apply the adult fixed value of 25 or 30kg/m2 of body mass index (BMI) as the overweight (Ow)or OB criteria. The world Health Organization (wHO)recommended the use of BMI-SDS or BMI z-score as ameasure of relative adjusted weight for the child%u2019s ageand sex. The interpretation cutoffs are as follows: O> + 1 SD (equivalent to BMI 25 kg/m2 at 19 years), OB:> 2 SD (equivalent to BMI 30 kg/m2 at 19 years) (16).In the United States, childhood OB has tripled since1980 for adolescents and doubled for children (17). Inthe European Region, according to wHO report, one inthree children aged 6-9 years had Ow or OB (18). In thestudy on nutrition, physical activity, child developmentand OB in Spain (ALADINO) report, the figures for Spainwere 23,3% of children with Ow and 17,2% with OB(19). According to the Childhood Obesity SurveillanceInitiative (COSI), Ow and OB affect 29% of children aged7-9 years old in the European region (20).Pediatric OB is associated with serious consequencesfor health and social life and is a global public healthchallenge due to its relationship with premature deathand disability in adulthood (18). Children who are OBare more likely to suffer from glucose intolerance, nonalcoholic fatty liver disease, dyslipidemia,hypertension, and cardiovascular disease (21).Considering that childhood OB persists into adulthood,prevention is essential for amelioration of this globalproblem. There are a variety of treatments for OB,mainly lifestyle modifications, medication, education,and counseling. Recent studies have proven that familyimplication, as well as intensive counseling incombination with behavior and lifestyle changes (dietand exercise) are the most effective strategies forweight loss.The objective of this systematic review is tosummarize the evidence on gut microbiota compositionin a pediatric population with Ow or OB. Thisknowledge could be useful for designing strategies toprevent or treat microbiota dysbiosis.1. INTRODUCTION1.1. Gut microbiotaThe human microbiome consists of bacteria, viruses,fungi, protozoa, and archaea that colonize thegastrointestinal tract, as well as other parts of the bodysuch as airways and skin. From the first days of life, itgradually matures and develops accordingly toindividual growth (1). Currently, there are more than1000 defined species that can be grouped into fivepredominant phyla: Firmicutes, Bacteroidetes,Verrucomicrobia, Actinobacteria and Proteobacteria(2).Postnatal intestinal colonization is determined bycomplex factors, some of which include the mother%u2019sdiet during pregnancy and lactation, the type ofdelivery, early skin-to-skin contact, weaning period, useof antibiotics during infancy, environment, and familymembers living in the same household (3,4). Thecolonization of the neonate by microbes is thebeginning of a lifelong human-microbe symbiosis (5).while human-specific gut microbiome composition candiffer, the variation itself is considered physiological inthe context of a healthy gut microbiota according toage, sex, ethnicity, climate, and lifestyle -dietaryhabits, among others (2).The human microbiota helps maintain health andwell-being. More importantly, our microbes havemetabolic activities and can synthetize importantmetabolites that can have an effect in the host (6).They participate in the control of our metabolism, howwe digest and store nutrients. They can metabolize bilesalts which affect our fat metabolism, synthesizevitamin K which helps in coagulation, degrade proteinto amino acids, ferment polysaccharides which wecannot digest, and produce short chain fatty acids(SCFA) (6). Some of them, such as butyrate andpropionate, can provide energy to epithelial cells andinduce satiety (2). Moreover, there is evidence that ourintestinal bacteria are capable of producing serotonin,melatonin, acetylcholine, and gamma-aminobutyricacid (GABA) which affect appetite regulation or bodyweight (6).In obesity (OB) and its associated comorbidities, thecomposition of gut microbiota and intestinal epithelialbarrier functions are altered, which is known as%u201cdysbiosis%u201d (7%u201310). Dysbiosis can be defined as adecrease in microbial diversity, reduced beneficialbacteria, and an increase in proinflammatory species(bacteria that become pathogenic under certainconditions) (10). while there is no clear understandingof a %u201chealthy%u201d colonic microbiota, several gutmicrobiota species may be associated with OB (11).Specifically, several gut microbiota metabolites couldparticipate in the induction of a low-grade chronic126ANALESRANFwww.analesranf.comComposici%u00f3n de la microbiota intestinal en poblaciones pedi%u00e1tricas con obesidad: una revisi%u00f3n sistem%u00e1ticaMarti A., Canas I y Tamez H.An. R.Acad. Farm.Vol. 90. n%u00ba 1 (2024) %u00b7 pp. 125-135