8 Type 2 Diabetes,Metformin,and Gut Microbiota Diabetes Care mice showed that an increase in the co n conclusion.our study of Colombian Prior Presentation.Parts of this study wer onic production of SCFAs,especially bu- adults provides eviden sented at the yrate and pro ery homeostasisand he nentation of mucin-dera glucose production Reference appetite body A.muciniphila as well as several SCFA Acetat ng b lo a mediated by epithelia celland antidiabetes and anti-inflammatory effects hehost agains ,U￥Cai01310906 34 5tud85w90556 ota in type pithelial metabolism and dep intra n of the agenc et a ranscri ng ment Forem nN,Vogens FK,van den Berg FW w levels of butyrate-producing ba ut mic e De n assodated with col on of SCFAs in dis tance (39,40) ta cha study is not without limit ata that cannot nrovide causal infer ng by m Korbonits M.Metfo od microbiota associations were Inst cancer.Nat Rev 010:14 argely consistent wheth event not due to confo t by ind funded by Grupo Em we ca other limitation to our study was the lack 307-32 of information on dose and duration of nl,analysis,orinterpretationotthed 201522 K.Molecula ud hav submit the of action hts? 2013:56:189 21ggrnen or ciation(att ation to ee H s of G En rd the P E 。Future studies are No othe nted to 6 of the tributions.Jd.l.C.Z. essed atealceaPobe revious obs on this an N.T.M (Forslund et a alyzed 4 gu I.Lack type 2diabetes)and thus may have be erp ples t af gon and groed assoctions of microbial et a that were st er in mag rec ou abili ults from udies with our modest samplesi and uscript. thors read 6:3919 20 a different populatio 552 intestine is robust and replicable across diverse populations. ut-based oh mice showed that an increase in the co￾lonic production of SCFAs, especially bu￾tyrate and propionate, triggers intestinal gluconeogenesis, benefiting glucose and energy homeostasis and reducing hepatic glucose production, appetite, and body weight (37). Acetate produced by bifido￾bacteria improves the intestinal defense mediated by epithelial cells and protects the host against lethal infection (34). Also, SCFAs, particularly butyrate, stimulate epithelial metabolism and deplete intra￾cellular O2, resulting in stabilization of the transcription factor HIF-1 and increasing epithelial barrier function (38). In humans, low levels of butyrate-producing bacteria have been associated with colonic disease (e.g., inflammatory bowel disease), high￾lighting the role of SCFAs in disease resis￾tance (39,40). Our study is not without limitations. Our findings are based on observational data that cannot provide causal infer￾ence. We were able to reduce the po￾tential for confounding by matching on age, sex, and BMI. Because our metformin– gut microbiota associations were largely consistent whether we used as a reference group the T2D-met2 or ND participants, we believe our findings were not due to confounding by indi￾cation. However, we cannot rule out unmeasured or residual confounding. An￾other limitation to our study was the lack of information on dose and duration of metformin treatment. This limitation could have resulted in a weaker, more conservative, association (attenuation to￾ward the null) between metformin and gut microbiota composition and struc￾ture. Future studies are warranted to determine the dose-response of the metformin-microbiota relationship. We also had a small sample size relative to a previous observational study on this topic (Forslund et al. [6] analyzed 784 gut metagenomes of Danish, Swedish, and Chinese participants, of which, 199 had type 2 diabetes) and thus may have been underpowered to detect statistical sig￾nificance for measures of a diversity and associations of microbial composi￾tion that were smaller in magnitude. Nev￾ertheless, our ability to largely confirm hypotheses generated from previous studies with our modest sample size and in a different population suggests that the effect of metformin on the gut microbiota is robust and replicable across diverse populations. In conclusion, our study of Colombian adults provides evidence congruent with the hypothesis that metformin has direct effects on gut microbiota composition through augmentation of mucin-degrading A. muciniphila as well as several SCFA￾producing bacteria. Randomized controlled trials are needed to determine whether the antidiabetes and anti-inflammatory effects of metformin are mediated by the changes to gut microbiota composition. Acknowledgments. Foremost, the authors are indebted to all the participants who agreed to take part in this study. The authors also thank Natalia Zuluaga (Vidarium) for preselection of potential participants; Luz G. Betancur and Natalia E. Guarin (bothofVidarium)forhelpinparticipantrecruitment; ErikaM. Loaiza, Natalia Pareja, D. Tatiana Garcia, and Yuliana M. Franco (of Vidarium) for their invaluable help during field work; Amalia Toro, Connie J. Arboleda, and Ana C. Ochoa (of EPS SURA) for their help authorizing and coordinating activities within EPS SURA; and the administrative and laboratory staff of EPS SURA and Dinamica I.P.S. ´ The authors also acknowledge Paola A. Rios (student) and Giovanni Torres (employee) from the Instituto Colombiano de Medicina Tropical for their help with sample handling and pretreat￾ment and APOLO Scientific Computing Center of EAFIT University for hosting the bioinformatics resources for the study. Funding. This work was funded by Grupo Em￾presarial Nutresa, EPS SURA, and Dinamica I.P.S. ´ The funders have not had any role in designing or conducting the study; in the collection, man￾agement, analysis, or interpretation of the data; in the preparation, review, or approval of the manuscript; or in the decision to submit the manuscript for publication. Duality of Interest. J.d.l.C.-Z., V.C.-A., E.P.V.-M., and J.S.E. are employees of Grupo Empresarial Nutresa. J.A.C. is an employee of Dinamica I.P.S. ´ J.M.A. is an employee of EPS SURA. No other potential conflicts of interest relevant to this article were reported. Author Contributions. J.d.l.C.-Z. processed fecal samples and DNA sequences, performed analyses, and wrote the manuscript. N.T.M. conceived the study, put forward hypotheses to be tested, and wrote the manuscript. V.C.-A. designed the cohort study, recruited partici￾pants, coordinatedfield activities, collected fecal and blood samples, and measured anthropo￾metric variables. E.P.V.-M. processed fecal sam￾ples and DNA sequences. J.A.C. coordinated field activities and transport and treatment of sam￾ples. J.M.A. coordinated participant recruitment and field activities. 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