[en] Introduction: obesity and its related comorbidities (such as metabolic syndrome, cardiovascular disease and DM) are one of the leading causes of global morbidity and mortality, and have become a main challenge for 21st century Medicine and a threat to social wellbeing. Its rapidly increasing prevalence has raised concerns and has prompted scientists to look out for new etiologic factors and therapeutic targets, with gut microbiota taking central stage in recent years: indeed a certain profile of gut microbiota has been linked to obesity. Additionally, intestinal flora has also been mentioned as a potential mediator of the beneficial effect bariatric surgery has demonstrated in morbid obesity patients. In this systematic review, we aimed to explain how gut microbiota affects the development of obesity as well as investigating its role on the effects of bariatric surgery. Methods: in order to look into these two hypotheses, we carried out a comprehensive research of the main databases, including articles published up until December 2018. Results: our initial search resulted in a sum of 2011 papers, with 1476 of them referring to our first hypothesis and 535 alluding to the second one. After screening titles and/or abstracts, a final amount of 29 articles was included: 20 regarding obesity and gut microbiota and 9 in relation to microbiota and bariatric surgery. A full text screening and critical review of these articles was then performed on them before being incorporated. Conclusion: gut microbiota is heavily involved in the development of obesity through its participation in several pathways regarding energy uptake, hormone regulation and inflammatory cascades. However, whether having a certain microbiota profile can precipitate obesity or not remains contested. Literature suggests microbiota changes at lower taxonomic levels should be looked into, rather than changes at phylum level. As opposed to simple associations, complex multiomic analysis of biological big data (consisting of the study of microbiome, genome and epigenome among others) is required. On the other hand, bariatric surgery (notably Roux-en-Y gastric bypass rather than Sleeve gastrectomy) has shown to significantly remodel gut microbiota. Nevertheless, more and longer-term investigations are needed in order to fully understand gut microbiota's influence on surgery results and how to improve them.

[eu] Sarrera: obesitatea eta berarekin erlazionaturiko patologiak (sindrome metabolikoa, gaixotasun kardiobaskularrak, DM) maila globalean morbi-mortalitate kausa nagusietako bat dira, gaur egungo medikuntza eta gizartearen erronka handi bat bilakatuz. Azken urteetan jasaten ari den prebalentziaren handipenaren aurrean Zientzia azalpen etiologiko berrien bila aritu da eta hauen artean, hesteetako mikrobiotak bereganatu du ikertzaileen arreta. Aldi berean, obesitate morbidoaren terapia efektibo bakartzat hartzen den kirurgia bariatrikoak duen arrakastan ere inplikatu izan da hesteetako mikrobiota. Lan honek beraz bi hipotesi, bi ikergai izan ditu: alde batetik hesteetako mikrobiotak obesitatean daukan eragina eta bestetik kirurgia bariatrikoan duen eragina. Metodoa: bi hipotesiak ikertzeko, bakoitzaren inguruko errebisio bibliografiko bat burutu da. Helburu honekin datu-base nagusietan 2018ko abendura arte argitaraturiko literatura arakatu dugu. Emaitzak: gure hasierako bilaketak 2011 artikulu jaso zituen, 1476 lehen hipotesiaren inguruan eta 535 bigarren hipotesiaren inguruan. Titulu edo/eta abstractak irakurriz bahetu genituen artikuluak, emaitzatzat 29 artikulu lortuz: 20 obesitatea eta mikrobiotari buruz eta 9 mikrobiota eta kirurgia bariatrikoari buruz. Ostean artikulu hauen testu osoaren irakurketa kritikoa egin zen, eztabaida eginez eta ondorioak ateraz. Ondorioak: mikrobiotak eragin nabaria du obesitatearen garapenean energia bilketa, bide hormonal eta inflamatorio ezberdinetan duen efektuaren bitartez. Hala ere, mikrobiota obesogeniko perfil zehatz baten bilaketan desadostasunak daude. Alderdi honetan maila taxonomiko baxuen (filum mailatik beherago) analisia iradokitzen da, asoziazio sinplez haratago begiratuz eta datuen analisi multiomikoak (mikrobioma, genoma, epigenoma eta gainerako omak bateratuta) egiteko tresnak baliatuz. Beste alde batetik, kirurgia bariatrikoak sakonki erremodelatzen du hesteko mikrobiota, Roux-en-Y bypass gastrikoak gehiago eta egokiago Gastrektomia bertikalak baino. Dena den, ikerketa gehiago, sakonago eta epe luzeagokoak behar dira kirurgia bariatriko ezberdinek mikrobiotan duten eragina zehazteko.