Insights Into the Role of theMicrobiome in Obesityand Type 2 DiabetesDiabetes Care 201538159ndash165 | DOI 102337dc14-0769

The worldwide prevalence of obesity and type 2 diabetes mellitus (T2DM)continues to rise at an alarming pace Recently the potential role of the gutmicrobiome in these metabolic disorders has been identified Obesity isassociated with changes in the composition of the intestinal microbiota andthe obese microbiome seems to be more efficient in harvesting energy from thediet Lean male donor fecal microbiota transplantation (FMT) in males withmetabolic syndrome resulted in a significant improvement in insulin sensitivity inconjunction with an increased intestinal microbial diversity including a distinctincrease in butyrate-producing bacterial strains Such differences in gut micro-biota compositionmight function as early diagnosticmarkers for the developmentof T2DM in high-risk patients Products of intestinal microbes such as butyratemay induce beneficial metabolic effects through enhancement of mitochondrialactivity prevention of metabolic endotoxemia and activation of intestinalgluconeogenesis via different routes of gene expression and hormone regulationFuture research should focus on whether bacterial products (like butyrate) havethe same effects as the intestinal bacteria that produce it in order to ultimatelypave the way for more successful interventions for obesity and T2DM The rapiddevelopment of the currently available techniques including use of fecaltransplantations has already shown promising results so there is hope for noveltherapies based on the microbiota in the future

The rising prevalence of type 2 diabetes mellitus (T2DM) continues to be a growingconcern worldwide From 1980 to 2008 the number of people diagnosed with di-abetes of which 90 type 2 has increased from 153 (123ndash182) million to 347 (314ndash382) million (1) The proportional increase in prevalence of obesity (between 1980and 2008 this has nearly doubled to more than half a billion people in the world)shows weight gain and changes in dietary habits to be the main contributing factorsto this alarming trend The resulting metabolic disorders like dyslipidemia and in-sulin resistance both part of the metabolic syndrome are a major risk factor forassociated diseases such as cardiovascular pathology nonalcoholic fatty liver dis-ease and different types of cancer (23) Themain cause for the obesity and diabetesepidemic has been attributed to economic and lifestyle changes in the last decadesincluding the decrease in physical activity combined with a growing availability offood high in calories However it appears to be extremely difficult for people tovoluntarily change their lifestyle drastically in order to lose weight In this respectevidence of a powerful regulating biological system resisting these cognitive signalsin order to maintain body weight in a relatively strict range is substantial andgrowing (4) For this reason obesity is now considered a disease rather than a

1Department of Vascular Medicine AcademicMedical Center University of AmsterdamAmsterdam the Netherlands2Wallenberg Laboratory Sahlgrenska Center forCardiovascular and Metabolic Research Univer-sity of Goteborg Goteborg Sweden3Novo Nordisk Foundation Center for Basic Meta-bolic Research Section for Metabolic Receptologyand Enteroendocrinology Faculty of Health Sci-ences University of Copenhagen CopenhagenDenmark

Corresponding author Max Nieuwdorpmnieuwdorpamcuvanl

Received 26 March 2014 and accepted 9 July2014

copy 2015 by the American Diabetes AssociationReaders may use this article as long as the workis properly cited the use is educational and notfor profit and the work is not altered

Annick V Hartstra1 Kristien EC Bouter1

Fredrik Backhed23 and Max Nieuwdorp12

Diabetes Care Volume 38 January 2015 159

REV

IEW

willful choice which calls for further in-sight into the pathophysiological path-ways as this could lead to sorely needednovel therapeutic targetsA recently discovered partaker in this

process is the intestinal microbiome (2)The microbiome refers to the 1014

bacteria that reside in the human intes-tine comprising a bulk of genetic mate-rial larger than the human genome (5)Recently our knowledge of the micro-biome in relation to the function of thehuman (small) intestine (Fig 1) (6) hasincreased immensely due to the develop-ment of new analytical methods such ashigh-throughput metagenomic sequenc-ing (7) This has enabled researchers toidentify possible effects of the micro-biome on human metabolism includingits potential role in metabolic disorderslike obesity and T2DM In this reviewwe aim to provide deeper insight of rele-vance to clinicians by discussing severaltopics in a ldquobench to bedsiderdquo approachwithin this emerging field

DIAGNOSTIC VALUE OFINTESTINAL MICROBIOTA IN T2DM

Although bacteria are usually consideredas pathogens an essential symbiotic

interaction between the human hostand intestinal bacteria is the forging andmaintenance of the immune system inthe gut The first recognition came fromfindings in germ-free (GF) mice of defectsin the development and function of theirimmune system (8) Another crucial inter-action of gut microbiota is their endoge-nous metabolic function that enables thedigestion of food components such asplant polysaccharides which are other-wise nondegradable (9) In this respectit is interesting that studies in mice aswell as humans have shown that gut mi-crobiota differ in composition betweenobese and lean subjects (1011) In aleptin-deficient obob mouse model Leyet al (10) found a difference in the ratioof Bacteroidetes and Firmicutes the twodominant intestinal bacterial phyla Com-pared with their lean counterparts obesemice showed a decrease in Bacteroidetesand a corresponding increase in Firmicutes(10) When Ley et al (10) compared gutmicrobiota of obese humans to lean con-trols they found similar differences inthis ratio (12) Other studies in mice havecorroborated these results (13ndash16) How-ever other human studies have foundcontradicting data (17ndash19) and it is

considered that part of this controversyresults from both the variations in dietcomposition around the globe as well asdifferent methods used to determine mi-crobiota composition

The involvement of the microbiomein energy balance was further demon-strated in a study where it was foundthat GF mice were leaner comparedwith conventionally raised counter-parts despite a higher food intake Ad-ditionally when transferring intestinalbacteria from normal mice to GF coun-terparts an increase in body fat of 60was observed within 10ndash14 days eventhough food consumption was de-creased (20) These results have led tothe belief that the obese microbiome ismore efficient at yielding energy fromthe diet (1117) This was supported byfindings that the total body fat of GFmice colonized with ldquoobese microbiotardquoincreased significantly compared withthose colonized with ldquolean microbiotardquo(11) The technique used in these stud-ies in mice is known as fecal microbiotatransplantation (FMT) In humans FMTcan be regarded as a working tool todissect association from causality for anumber of diseases (21) The first clinicaluse was the successful treatment of pa-tients with pseudomembraneous colitisan unremitting infection with Clostrid-ium difficile usually following the useof antibiotics (22) Since then FMT hasbeen found effective in other chronicgastrointestinal infections and inflam-matory bowel diseases its therapeuticpotential being attributed to a restoringability of the gut microbial balance byreplacing pathogens with more benefi-cial bacterial strains (2123) Consider-ing the promising results of the effectsof FMT onmetabolism inmice a currentinterest in the clinical use of FMT forhumans is focusing on metabolic andcardiovascular disorders We recentlyperformed a double-blind randomizedcontrolled trial in insulin-resistant maleswith metabolic syndrome who receivedeither autologous or allogenic feces in-fusion from lean donors (24) Beneficialmetabolic effects were observed in thegroup receiving the lean donor trans-plantation including a significantly im-proved peripheral (muscle) insulinsensitivity This was accompanied by asignificantly increased intestinal micro-bial diversity along with a distinct in-crease in levels of butyrate-producing

Figure 1mdashDifferential functions of small and large intestine in relation tomicrobial density (6) Inthe proximal part of the small intestine (where only few intestinal bacterial strains reside)important metabolic functions take place such as uptake of dietary glucose lipids and proteinsMore distally in the colon (where the majority of intestinal bacterial strains reside) water isabsorbed from feces and SCFAs are produced via fermentation

160 Role of Microbiome in Obesity and T2DM Diabetes Care Volume 38 January 2015

bacteria such as Roseburia in the fecesand Eubacterium halii in the small intes-tine Interestingly not all lean donorsexerted the same beneficial effects inthe obese host Based on the small sam-ple size however one should take intoaccount that the reported effect mightbe due to a variation around a mean(meaning no clear effect of lean donorFMT when larger numbers of individualsare studied) On the other hand thesefindings might indicate the presence ofldquosuper fecal donorsrdquo a concept that iscurrently being studied at our depart-ments The results from this relativelysmall cohort of patients with metabolicsyndromeon the relation betweenmicro-bial diversity and amount of butyrate-producing bacteria are in linewith similarfindings in two large metagenome-wideassociation studies (2526) a type ofstudy where clinical data are combinedwithmetagenomic analysis Both Karlssonet al (25) and Qin et al (26) indepen-dently found a decrease of butyrate-producing bacteria namely Roseburiaand Faecalibacterium prauznitzii in thegut microbiota of patients with T2DMcompared with healthy subjects More-over we showed that increases in fecalconcentrations of Lactobacillus gasseriand Streptococcus mutans (both inhab-itants of the proximal intestine) as wellas Escherichia coliwere found to be pre-dictive of the development of insulinresistance in postmenopausal obeseCaucasian females in Sweden (see Table1) It should be noted however thatthese correlations are not very strongand have not been reproduced in othercohorts moreover it is not known atthis time whether these found changesin intestinal microbiota composition aresecondary to altered gastrointestinalmotility and small intestinal bacterialovergrowth often seen in T2DM Never-theless such intestinal bacterial strainsmight function as early diagnosticmarkers in the clinic for better identifi-cation of those obese subjects thatare prone to develop T2DM (26) Tostrengthen the predictive potential ofparticular patterns of microbial diversityand composition as well as pathogenicalterations of the microbiota composi-tion further research both in prospectivecohorts and therapeutic phase III inter-vention trials with specific bacterialstrains are urgently needed In this re-spect it is promising that an increasing

number of companies are starting to ap-pear that focus on the development ofintestinal microbiome diagnostics andtherapeutics (2728)

PRODUCTS OF INTESTINAL BACTERIAIN T2DM PATHOPHYSIOLOGY

Butyrate and acetate and propionate areshort-chain fatty acids (SCFAs) fermentedby the intestinal bacteria from dietary fi-ber that play an important role in energymetabolism (Fig 2) (29) These SCFAs areabsorbed in the intestine where particu-larly butyrate provides energy for thecolonic epithelial cells whereas theremaining SCFAs enter the (portal) ve-nous system Data from animal studieshave suggested that propionate affectshepatic lipogenesis and gluconeogenesiswhereas peripherally acetate functions assubstrate for cholesterol synthesis (17)The colonic mucosa primarily relies onthe luminal presence of butyrate as en-ergy source and a lack of these SCFAs hasbeen proposed to play an important partin the pathogenesis of intestinal diseaseand inflammatory bowel diseases (30)More specific low concentrations ofSCFAs have been found in ulcerative co-litis patients (31) and treatment withSCFA enemas especially butyrate hasbeen shown to reduce inflammation inthis patient group (32) Interestinglyoral administration of sodium butyratewas found to be safe and well toleratedin humans with Crohn disease and ulcer-ative colitis (3334) these studiesshowed a systemic anti-inflammatoryeffect and improved clinical improve-ment In mice oral butyrate has beendemonstrated to improve insulin sensi-tivity and increase energy expenditureby enhancing mitochondrial function(35) Whether these beneficial effectsapply to humans as well is currently

being studied in our department Theunderlying mechanisms of the potentialpositive influence of butyrate on me-tabolism are not clear However thereis data on inhibiting effects of butyrateon histone deacetylases in mammaliancultured cells which regulate gene ex-pression by deacetylating histone pro-teins and transcription factors (36) Thismay contribute to increased expressionof PGC-1a a transcription coactivatorassociated with increased fatty acid oxi-dation and mitochondrial activity (35)Butyrate being an SCFA is oxidized inthe mitochondria of colonocytes intoacetyl-CoA and via the tricarboxylic acidcycle contributes to ATP production Im-portant catalyzing enzymes in this processhave been shown to be downregulated inGF mice resulting in a significantly de-creased level of ATP in GF colonocytesThis indicates a potential stimulating roleof the intestinal microbiota particularlybutyrate-producing microbes in the ex-pression of these enzymes and conse-quently mitochondrial function andenergy metabolism (37) Another way inwhich SCFAs might influence the hostrsquosenergy balance is by acting as specific sig-naling products SCFAs bind to G proteinndashcoupled receptors namely GPR41 andGPR43 which are expressed in entero-endocrine cells in the intestinal epithe-lium (338) This leads to secretion ofcertain peptide hormones like PYYwhich are basolaterally released intothe systemic circulation enabling aform of communication between gut mi-lieu and host Conventional Gpr4122

mice and GF Gpr4122 mice colonizedwith members of the human gut micro-biota stayed significantly leaner than theirwild-type counterparts whereas no differ-ences were seen between wild type andGF Gpr4122 mice The latter indicates a

Table 1mdashIntestinal bacterial species associated with andor predictive of insulinresistanceT2DM development as future potential clinical diagnostic markers ofT2DM

Increase in T2DM Decrease in T2DM

Intestinal bacterial phylaFirmicutes xBacteroidetes x

Intestinal bacterial species Increase in T2DM Decrease in T2DMRoseburia xEubacterium halii xFaecalibacterium prauznitzii xLactobacillus gasseri xStreptococcus mutans xE coli x

carediabetesjournalsorg Hartstra and Associates 161

bacteria such as Roseburia in the fecesand Eubacterium halii in the small intes-tine Interestingly not all lean donorsexerted the same beneficial effects inthe obese host Based on the small sam-ple size however one should take intoaccount that the reported effect mightbe due to a variation around a mean(meaning no clear effect of lean donorFMT when larger numbers of individualsare studied) On the other hand thesefindings might indicate the presence ofldquosuper fecal donorsrdquo a concept that iscurrently being studied at our depart-ments The results from this relativelysmall cohort of patients with metabolicsyndromeon the relation betweenmicro-bial diversity and amount of butyrate-producing bacteria are in linewith similarfindings in two large metagenome-wideassociation studies (2526) a type ofstudy where clinical data are combinedwithmetagenomic analysis Both Karlssonet al (25) and Qin et al (26) indepen-dently found a decrease of butyrate-producing bacteria namely Roseburiaand Faecalibacterium prauznitzii in thegut microbiota of patients with T2DMcompared with healthy subjects More-over we showed that increases in fecalconcentrations of Lactobacillus gasseriand Streptococcus mutans (both inhab-itants of the proximal intestine) as wellas Escherichia coliwere found to be pre-dictive of the development of insulinresistance in postmenopausal obeseCaucasian females in Sweden (see Table1) It should be noted however thatthese correlations are not very strongand have not been reproduced in othercohorts moreover it is not known atthis time whether these found changesin intestinal microbiota composition aresecondary to altered gastrointestinalmotility and small intestinal bacterialovergrowth often seen in T2DM Never-theless such intestinal bacterial strainsmight function as early diagnosticmarkers in the clinic for better identifi-cation of those obese subjects thatare prone to develop T2DM (26) Tostrengthen the predictive potential ofparticular patterns of microbial diversityand composition as well as pathogenicalterations of the microbiota composi-tion further research both in prospectivecohorts and therapeutic phase III inter-vention trials with specific bacterialstrains are urgently needed In this re-spect it is promising that an increasing

number of companies are starting to ap-pear that focus on the development ofintestinal microbiome diagnostics andtherapeutics (2728)

PRODUCTS OF INTESTINAL BACTERIAIN T2DM PATHOPHYSIOLOGY

Butyrate and acetate and propionate areshort-chain fatty acids (SCFAs) fermentedby the intestinal bacteria from dietary fi-ber that play an important role in energymetabolism (Fig 2) (29) These SCFAs areabsorbed in the intestine where particu-larly butyrate provides energy for thecolonic epithelial cells whereas theremaining SCFAs enter the (portal) ve-nous system Data from animal studieshave suggested that propionate affectshepatic lipogenesis and gluconeogenesiswhereas peripherally acetate functions assubstrate for cholesterol synthesis (17)The colonic mucosa primarily relies onthe luminal presence of butyrate as en-ergy source and a lack of these SCFAs hasbeen proposed to play an important partin the pathogenesis of intestinal diseaseand inflammatory bowel diseases (30)More specific low concentrations ofSCFAs have been found in ulcerative co-litis patients (31) and treatment withSCFA enemas especially butyrate hasbeen shown to reduce inflammation inthis patient group (32) Interestinglyoral administration of sodium butyratewas found to be safe and well toleratedin humans with Crohn disease and ulcer-ative colitis (3334) these studiesshowed a systemic anti-inflammatoryeffect and improved clinical improve-ment In mice oral butyrate has beendemonstrated to improve insulin sensi-tivity and increase energy expenditureby enhancing mitochondrial function(35) Whether these beneficial effectsapply to humans as well is currently

being studied in our department Theunderlying mechanisms of the potentialpositive influence of butyrate on me-tabolism are not clear However thereis data on inhibiting effects of butyrateon histone deacetylases in mammaliancultured cells which regulate gene ex-pression by deacetylating histone pro-teins and transcription factors (36) Thismay contribute to increased expressionof PGC-1a a transcription coactivatorassociated with increased fatty acid oxi-dation and mitochondrial activity (35)Butyrate being an SCFA is oxidized inthe mitochondria of colonocytes intoacetyl-CoA and via the tricarboxylic acidcycle contributes to ATP production Im-portant catalyzing enzymes in this processhave been shown to be downregulated inGF mice resulting in a significantly de-creased level of ATP in GF colonocytesThis indicates a potential stimulating roleof the intestinal microbiota particularlybutyrate-producing microbes in the ex-pression of these enzymes and conse-quently mitochondrial function andenergy metabolism (37) Another way inwhich SCFAs might influence the hostrsquosenergy balance is by acting as specific sig-naling products SCFAs bind to G proteinndashcoupled receptors namely GPR41 andGPR43 which are expressed in entero-endocrine cells in the intestinal epithe-lium (338) This leads to secretion ofcertain peptide hormones like PYYwhich are basolaterally released intothe systemic circulation enabling aform of communication between gut mi-lieu and host Conventional Gpr4122

mice and GF Gpr4122 mice colonizedwith members of the human gut micro-biota stayed significantly leaner than theirwild-type counterparts whereas no differ-ences were seen between wild type andGF Gpr4122 mice The latter indicates a

Table 1mdashIntestinal bacterial species associated with andor predictive of insulinresistanceT2DM development as future potential clinical diagnostic markers ofT2DM

Increase in T2DM Decrease in T2DM

Intestinal bacterial phylaFirmicutes xBacteroidetes x

Intestinal bacterial species Increase in T2DM Decrease in T2DMRoseburia xEubacterium halii xFaecalibacterium prauznitzii xLactobacillus gasseri xStreptococcus mutans xE coli x

carediabetesjournalsorg Hartstra and Associates 161

regulating role of GPR41 in energy ho-meostasis in relation to the intestinal mi-crobiota and their metabolic productsFurthermore Gpr4122 deficiency wasassociated with a decrease in the gut-derived hormone PYY resulting in a de-creased extraction of energy from thediet associated with an increase in intes-tinal transit time (39)Another function of butyrate which

may contribute to its possible beneficialrole in the hostrsquos metabolism is main-taining intestinal integrity This contrib-utes to the prevention of endotoxemia aprocess resulting from translocation ofendotoxic compounds (lipopolysaccha-rides [LPS]) of gram-negative intestinalbacteria In the last decade it has becomeevident that insulin resistance and T2DMare characterized by low-grade inflamma-tion (40) In this respect LPS trigger a low-grade inflammatory response and the

process of endotoxemia can therefore re-sult in the development of insulin resis-tance and other metabolic disorders(4142) Butyrate also seems to play apart in the recent discovery of the intes-tinersquos ability to produce glucose itselfGlucose released by intestinal gluconeo-genesis (IGN) is detected by a portal veinglucose sensor that signals to the brainthrough the peripheral nervous systemthus positively influencing glucose me-tabolism and intake of food (43) DeVadder et al (44) confirmed in rats thebeneficial effects of SCFAs and IGN onglucose metabolism and subsequentlyshowed that butyrate is involved by ac-tivating gene expression of IGN in miceHowever these findings still need vali-dation in humans and we are currentlyexecuting a study in which we havetreated subjects with metabolic syn-drome for 4 weeks with oral butyrate

to study its effects on insulin sensitivityand microbiota composition

INNOVATIVE STRATEGIES FORNOVEL THERAPEUTICS IN T2DM

Interestingly in animal models buty-rate has also been shown to both affectintestinal serotonin levels (45) and in-crease serotonin transporters (SERTs)in the hypothalamus (46) Furthermorebutyrate directly affects sympathetictone and intestinal transit times (47) aswell as physical activity (48) In line it isknown that serotonin itself can regulateintestinal permeability (49) besides beingan important signaling neurotransmitterin the gut and brain involved in regula-tion of body weight and food intake byenhancing satiety (50) A reduction in ce-rebral SERTs essential regulators of sero-tonergic transmission is associated withobesity (51) In a human study whenhealthy lean subjects received a hyper-caloric snacking diet for 6 weeks a signif-icant 30 decrease of hypothalamic SERTbinding was seen (52)

In this respect it is interesting to notethat studies have suggested a regulatinginfluence of intestinal bacteria on sero-tonin (5354) For example bariatric sur-gery (Roux-en-Y gastric bypass [RYGB])has been shown to significantly affectserotonin metabolism in both animals(5155) and humans (56) MoreoverRYGB is regarded as a last resort butvery successful treatment for morbidlyobese patients because next to inducingweight loss up to 50 of the originalweight it also decreases the risk ofT2DM and cardiovascular pathology(5758) RYGB has even been shown toresolve insulin resistance faster than theactual weight loss underscoring a poten-tial weight-independent effect on me-tabolism (4158) As RYGB can alter thecomposition of the gut microbiota inboth mice (59) and humans (6061)this might be one of the contributingfactors When diabetic mice were colo-nized with feces of post-RYGBmice theylost weight and showed improvement inglucose and lipid metabolism with spe-cific changes in butyrate-producing bac-teria (59) These findings suggest thatthe change in butyrate-producing micro-biota after RYGB may play an importantrole in satiety as well as regulation ofglucose and lipid metabolism

It is thus becoming increasingly evi-dent that the composition of gut

Figure 2mdashRole of gut microbiotandashproduced SCFAs in human glucose metabolism in obesesubjects Fermentation of dietary fibers by intestinal bacteria generates SCFAs including buty-rate that have both metabolic and epigenetic effects Obese insulin-resistant subjects arecharacterized by altered SCFA production compared with lean subjects We hypothesize thatin these subjects this adversely affects satiety hepatic glucose and lipid production as well asinflammatory tone

162 Role of Microbiome in Obesity and T2DM Diabetes Care Volume 38 January 2015

microbiota plays a role in the regulationof glucose and lipid metabolism Specif-ically there seems to be an associationbetween butyrate-producing bacteriaand beneficial effects on metabolism inboth mice and humans (2435) Further-more an alteration in the compositionof the gut microbiota may be involved inthe development of obesity and T2DMFurther studies are however needed toestablish the causality of this and as towhether increasing intestinal SCFAs in-cluding butyrate has the same meta-bolic influence as SCFA-producingbacteria on human metabolism includ-ing insulin sensitivity and inflammatorytone Thus in order to validate the hy-pothesis of butyrate-producing bacteriaas role players and their products as sig-naling molecules in human glucose andlipid metabolism double-blinded ran-domized controlled trials using eitherSCFA supplementation (given eitherorally or rectally) or FMT derived fromdifferent donors (eg on different diets)are needed Priorities for further studiesalso include therapeutic interventiontrials with specific types of single bacte-rial strains in order to elucidate particu-lar beneficial patterns in gut microbiotacompositionOther areas of therapeutic interest

in this respect are nondigestible butfermentable fibers such as inulin fructo-oligosaccharides galacto-oligosaccharidesand lactulose Food artificially enrichedwith these fibers has been termed aprebiotic when it is able to shift thecomposition of gut microbiota by stim-ulating the growth or activity of ben-eficial species (23) In this respectcarbohydrate-fermenting bacteria suchas Bifidobacteria and Lactobacilli in-crease upon prebiotic treatment in dif-ferent age-groups (62) The effectsof prebiotics have been ascribed to animmune-mediated mechanism As pre-viously mentioned high-fat dietaryfeeding is associated with endotoxemiawhich in turn is linked to a reducedabundance of Bifidobacteriawith a con-comitant increase in gram-negative(LPS-containing) bacteria In line whenprebiotic-containing oligofructose (OFS)were fed to mice on a high-fat diet thisrestored levels of their Bifidobacteriaand consequently reduced endotoxemiaand improved glucose tolerance (63)Another line of therapeutic approach

is probiotics which encompass food

supplements enriched with strains oflive bacteria including species of Bifido-bacteria and Lactobacilli that are ableto alter the gut microbiota beneficiallyfor the host (2864) In mice antidia-betic effects have been shown followingadministration of probiotics containingcertain Lactobacillus strains (65) with aconcomitant reduction in endotoxemia(66) Due to the placebo effect of theseproducts proper double-blinded ran-domized controlled trials with acceptedhard end points are needed in humansto address the potentially beneficialmetabolic effects of probiotic strains inrelation to the composition of the intes-tinal microbiota

Although public health has benefitedsubstantially from the discovery of anti-biotics its rapid increase in use is start-ing to raise health concerns Next to theobvious issue of antibiotic resistance itsworldwide use might potentially be as-sociated with the obesity epidemic (67)Although oral antibiotic treatment ef-fectively eradicates pathogenic bacte-ria the beneficial intestinal microbialcommunity is also affectedwith possibledire metabolic consequences Long-term intravenous vancomycin (aimedat gram-positive bacteria) in adult pa-tients was linked to an increased riskof developing obesity (68) whereasamoxicillin (aimed at gram-negativeand anaerobic bacteria) had only minoreffects In line short-term oral adminis-tration of vancomycin (but not amoxicil-lin) significantly impaired peripheralinsulin sensitivity via altered bile aciddehydroxylation in males with meta-bolic syndrome which was associatedwith a changed gut microbiota compo-sition (69) Moreover even short-termcourses of oral antibiotics were shownto have profound (irreversible) effectson intestinal microbial diversity andcomposition (70) The recent data link-ing use of antibiotics in early infancy todistinct long-term effects on intestinalmicrobiota diversity and the risk ofchildhood overweight (71) are evenmore alarming but not surprising Inthe last 50 years the use of subthera-peutic antibiotic therapy in farm animalshas become widely used as it increasesgrowth and therefore food productionIn mice treatment with subtherapeuticdoses of antibiotics alters the composi-tion of the intestinal microbiota andtherefore affects metabolic pathways

particularly concerning SCFA metabo-lism (72) These findings emphasize thecausal relationship between metabo-lism and the gut microbiome and amore cautionary use of antibioticsseems to be more justified than ever

However the simplest solution to re-storing pathological disturbances in thecomposition of the gut microbiota maybe a change in dietary habits Diet hasbeen shown to strongly affect the com-position of the microbiome (73) Whenobese humans were put either on a fat-restricted or carbohydrate-restrictedlow-calorie diet an increase in the abun-dance of Bacteroidetes and a decreasein Firmicutes was reported (12) In an-other study diet-induced weight lossversus weight-stabilization interven-tions in obese humans increased intes-tinal microbial gene richness and wasassociated with a reduced systemicinflammation (74) These data corrobo-rate with another controlled diet inter-vention study in 98 human subjectsshowing that certain dominant gut mi-crobial communities or ldquoenterotypesrdquocorrelated with specific kinds of diets(73) For example Bacteroideswas asso-ciated with a protein-rich diet whereasPrevotella correlated with a fiber-richdiet moreover gut microbiota compo-sition could be altered within 24 hwhereas enterotype remained stableduring the 10 days of the study Basedon this rapid and dramatic plasticityof intestinal microbiota compositionthere is a specific need to determineintestinal microbiota compositionin a standardized way (eg sequencingseveral fecal samples per personover a specific time point while takingdietary intake and medication use intoaccount)

CONCLUSIONS

The determination of the intestinal mi-crobiome in obesity and T2DM has ledto an exponential increase of scientific re-search in this area In this review we triedto cover several topics in order to provideclinically relevant insight A multitude ofstudies has revealed various potentialmechanisms ranging from endocrineand metabolic pathways to mechanismson a cellular and genetic level Our un-derstanding of environmental factors af-fecting the microbiome such as our dietrepetitive infections and the use of anti-biotics is improving and will hopefully

carediabetesjournalsorg Hartstra and Associates 163

microbiota plays a role in the regulationof glucose and lipid metabolism Specif-ically there seems to be an associationbetween butyrate-producing bacteriaand beneficial effects on metabolism inboth mice and humans (2435) Further-more an alteration in the compositionof the gut microbiota may be involved inthe development of obesity and T2DMFurther studies are however needed toestablish the causality of this and as towhether increasing intestinal SCFAs in-cluding butyrate has the same meta-bolic influence as SCFA-producingbacteria on human metabolism includ-ing insulin sensitivity and inflammatorytone Thus in order to validate the hy-pothesis of butyrate-producing bacteriaas role players and their products as sig-naling molecules in human glucose andlipid metabolism double-blinded ran-domized controlled trials using eitherSCFA supplementation (given eitherorally or rectally) or FMT derived fromdifferent donors (eg on different diets)are needed Priorities for further studiesalso include therapeutic interventiontrials with specific types of single bacte-rial strains in order to elucidate particu-lar beneficial patterns in gut microbiotacompositionOther areas of therapeutic interest

in this respect are nondigestible butfermentable fibers such as inulin fructo-oligosaccharides galacto-oligosaccharidesand lactulose Food artificially enrichedwith these fibers has been termed aprebiotic when it is able to shift thecomposition of gut microbiota by stim-ulating the growth or activity of ben-eficial species (23) In this respectcarbohydrate-fermenting bacteria suchas Bifidobacteria and Lactobacilli in-crease upon prebiotic treatment in dif-ferent age-groups (62) The effectsof prebiotics have been ascribed to animmune-mediated mechanism As pre-viously mentioned high-fat dietaryfeeding is associated with endotoxemiawhich in turn is linked to a reducedabundance of Bifidobacteriawith a con-comitant increase in gram-negative(LPS-containing) bacteria In line whenprebiotic-containing oligofructose (OFS)were fed to mice on a high-fat diet thisrestored levels of their Bifidobacteriaand consequently reduced endotoxemiaand improved glucose tolerance (63)Another line of therapeutic approach

is probiotics which encompass food

supplements enriched with strains oflive bacteria including species of Bifido-bacteria and Lactobacilli that are ableto alter the gut microbiota beneficiallyfor the host (2864) In mice antidia-betic effects have been shown followingadministration of probiotics containingcertain Lactobacillus strains (65) with aconcomitant reduction in endotoxemia(66) Due to the placebo effect of theseproducts proper double-blinded ran-domized controlled trials with acceptedhard end points are needed in humansto address the potentially beneficialmetabolic effects of probiotic strains inrelation to the composition of the intes-tinal microbiota

Although public health has benefitedsubstantially from the discovery of anti-biotics its rapid increase in use is start-ing to raise health concerns Next to theobvious issue of antibiotic resistance itsworldwide use might potentially be as-sociated with the obesity epidemic (67)Although oral antibiotic treatment ef-fectively eradicates pathogenic bacte-ria the beneficial intestinal microbialcommunity is also affectedwith possibledire metabolic consequences Long-term intravenous vancomycin (aimedat gram-positive bacteria) in adult pa-tients was linked to an increased riskof developing obesity (68) whereasamoxicillin (aimed at gram-negativeand anaerobic bacteria) had only minoreffects In line short-term oral adminis-tration of vancomycin (but not amoxicil-lin) significantly impaired peripheralinsulin sensitivity via altered bile aciddehydroxylation in males with meta-bolic syndrome which was associatedwith a changed gut microbiota compo-sition (69) Moreover even short-termcourses of oral antibiotics were shownto have profound (irreversible) effectson intestinal microbial diversity andcomposition (70) The recent data link-ing use of antibiotics in early infancy todistinct long-term effects on intestinalmicrobiota diversity and the risk ofchildhood overweight (71) are evenmore alarming but not surprising Inthe last 50 years the use of subthera-peutic antibiotic therapy in farm animalshas become widely used as it increasesgrowth and therefore food productionIn mice treatment with subtherapeuticdoses of antibiotics alters the composi-tion of the intestinal microbiota andtherefore affects metabolic pathways

particularly concerning SCFA metabo-lism (72) These findings emphasize thecausal relationship between metabo-lism and the gut microbiome and amore cautionary use of antibioticsseems to be more justified than ever

However the simplest solution to re-storing pathological disturbances in thecomposition of the gut microbiota maybe a change in dietary habits Diet hasbeen shown to strongly affect the com-position of the microbiome (73) Whenobese humans were put either on a fat-restricted or carbohydrate-restrictedlow-calorie diet an increase in the abun-dance of Bacteroidetes and a decreasein Firmicutes was reported (12) In an-other study diet-induced weight lossversus weight-stabilization interven-tions in obese humans increased intes-tinal microbial gene richness and wasassociated with a reduced systemicinflammation (74) These data corrobo-rate with another controlled diet inter-vention study in 98 human subjectsshowing that certain dominant gut mi-crobial communities or ldquoenterotypesrdquocorrelated with specific kinds of diets(73) For example Bacteroideswas asso-ciated with a protein-rich diet whereasPrevotella correlated with a fiber-richdiet moreover gut microbiota compo-sition could be altered within 24 hwhereas enterotype remained stableduring the 10 days of the study Basedon this rapid and dramatic plasticityof intestinal microbiota compositionthere is a specific need to determineintestinal microbiota compositionin a standardized way (eg sequencingseveral fecal samples per personover a specific time point while takingdietary intake and medication use intoaccount)

CONCLUSIONS

The determination of the intestinal mi-crobiome in obesity and T2DM has ledto an exponential increase of scientific re-search in this area In this review we triedto cover several topics in order to provideclinically relevant insight A multitude ofstudies has revealed various potentialmechanisms ranging from endocrineand metabolic pathways to mechanismson a cellular and genetic level Our un-derstanding of environmental factors af-fecting the microbiome such as our dietrepetitive infections and the use of anti-biotics is improving and will hopefully

carediabetesjournalsorg Hartstra and Associates 163

contribute to finding a solution for theglobal obesity epidemic

Funding AVH is supported by an FP7-EUconsortium grant (MyNewGut) FB is sup-ported by the Swedish Research Council Swed-ish Diabetes Foundation Swedish Heart LungFoundation Swedish Foundation for StrategicResearch Knut and Alice Wallenberg Founda-tion Goran Gustafsson Foundation Ingabritt andArne Lundbergrsquos Foundation Swedish Heart-LungFoundation Torsten Soderbergrsquos FoundationRagnar Soderbergrsquos Foundation Novo NordiskFoundation AFA Insurances and LUA-ALF grantsfrom Vastra Gotalandsregionen and StockholmCounty Council FB is a recipient of a EuropeanResearch Council consolidator grant (615362-METABASE) MN is supported by a VIDI grant2013 (016146327) aswell as a CVON2012 grant(IN-CONTROL)Duality of Interest FB is a founder of andowns equity in MetaboGen AB MN is afounder of and owns equity in Caelus Pharma-ceuticals and he is member of the SAB of SeresHealth Inc No other potential conflicts ofinterest relevant to this article were reportedAuthor Contributions AVH and KECBperformed research and drafted the manuscriptFB and MN supervised the writing of themanuscript

References1 Danaei G Finucane MM Lu Y et al GlobalBurden ofMetabolic Risk Factors of Chronic Dis-eases Collaborating Group (Blood Glucose) Na-tional regional and global trends in fastingplasma glucose and diabetes prevalence since1980 systematic analysis of health examinationsurveys and epidemiological studies with 370country-years and 2z7 million participants Lan-cet 201137831ndash402 Palermo A Maggi D Maurizi AR Pozzilli PBuzzetti R Prevention of type 2 diabetes melli-tus is it feasible Diabetes Metab Res Rev 201430(Suppl 1)4ndash123 Tilg H Kaser A Gut microbiome obesity andmetabolic dysfunction J Clin Invest 20111212126ndash21324 Friedman JM Modern science versus thestigma of obesity Nat Med 200410563ndash5695 Zhu B Wang X Li L Human gut microbiomethe second genome of human body Protein Cell20101718ndash7256 Simren M Barbara G Flint HJ et al RomeFoundation Committee Intestinal microbiota infunctional bowel disorders a Rome foundationreport Gut 201362159ndash1767 Claesson MJ OrsquoToole PW Evaluating the lat-est high-throughput molecular techniques forthe exploration of microbial gut communitiesGut Microbes 20101277ndash2788 Lee YK Mazmanian SK Has the microbiotaplayed a critical role in the evolution of theadaptive immune system Science 20103301768ndash17739 Flint HJ Bayer EA Rincon MT Lamed RWhite BA Polysaccharide utilization by gut bac-teria potential for new insights from genomicanalysis Nat Rev Microbiol 20086121ndash131

10 Ley RE Backhed F Turnbaugh P LozuponeCA Knight RD Gordon JI Obesity alters gut mi-crobial ecology Proc Natl Acad Sci U S A 200510211070ndash1107511 Turnbaugh PJ Ley RE Mahowald MAMagrini V Mardis ER Gordon JI An obesity-associated gut microbiome with increased ca-pacity for energy harvest Nature 20064441027ndash103112 Ley RE Turnbaugh PJ Klein S Gordon JIMicrobial ecology human gut microbes associ-ated with obesity Nature 20064441022ndash102313 Turnbaugh PJ Backhed F Fulton L GordonJI Diet-induced obesity is linked to marked butreversible alterations in the mouse distal gutmicrobiome Cell Host Microbe 20083213ndash22314 Turnbaugh PJ Ridaura VK Faith JJ Rey FEKnight R Gordon JI The effect of diet on thehuman gut microbiome a metagenomic analy-sis in humanized gnotobiotic mice Sci TranslMed 200916ra1415 Fleissner CK Huebel N Abd El-Bary MMLoh G Klaus S Blaut M Absence of intestinalmicrobiota does not protect mice from diet-induced obesity Br J Nutr 2010104919ndash92916 Hildebrandt MA Hoffmann C Sherrill-MixSA et al High-fat diet determines the composi-tion of the murine gut microbiome indepen-dently of obesity Gastroenterology 20091371716ndash1724e1ndash217 Schwiertz A Taras D Schafer K et al Micro-biota and SCFA in lean and overweight healthysubjects Obesity (Silver Spring) 201018190ndash19518 Arumugam M Raes J Pelletier E et alMetaHIT Consortium Enterotypes of the humangut microbiome Nature 2011473174ndash18019 Duncan SH Belenguer A Holtrop GJohnstone AM Flint HJ Lobley GE Reduced di-etary intake of carbohydrates by obese subjectsresults in decreased concentrations of butyrateand butyrate-producing bacteria in feces ApplEnviron Microbiol 2007731073ndash107820 Backhed F Ding H Wang T et al The gutmicrobiota as an environmental factor that reg-ulates fat storage Proc Natl Acad Sci U S A 200410115718ndash1572321 Smits LP Bouter KEC de Vos WM BorodyTJ Nieuwdorp M Therapeutic potential of fecalmicrobiota transplantation Gastroenterology2013145946ndash95322 van Nood E Vrieze A Nieuwdorp M et alDuodenal infusion of donor feces for recurrentClostridium difficile N Engl J Med 2013368407ndash41523 Kootte RS Vrieze A Holleman F et al Thetherapeutic potential of manipulating gut mi-crobiota in obesity and type 2 diabetes mellitusDiabetes Obes Metab 201214112ndash12024 Vrieze A Van Nood E Holleman F et alTransfer of intestinal microbiota from lean do-nors increases insulin sensitivity in individualswith metabolic syndrome Gastroenterology2012143913ndash916e725 Karlsson FH Tremaroli V Nookaew I et alGut metagenome in European women with nor-mal impaired and diabetic glucose control Na-ture 201349899ndash10326 Qin J Li Y Cai Z et al A metagenome-wideassociation study of gut microbiota in type 2diabetes Nature 201249055ndash6027 de VosWMNieuwdorpM Genomics A gutprediction Nature 201349848ndash49

28 Olle B Medicines from microbiota Nat Bio-technol 201331309ndash31529 Cummings JH Short chain fatty acids in thehuman colon Gut 198122763ndash77930 Scheppach W Effects of short chain fattyacids on gut morphology and function Gut199435(Suppl)S35ndashS3831 Vernia P Gnaedinger A Hauck W Breuer RIOrganic anions and the diarrhea of inflammatorybowel disease Dig Dis Sci 1988331353ndash135832 Scheppach W Sommer H Kirchner T et alEffect of butyrate enemas on the colonic mu-cosa in distal ulcerative colitis Gastroenterol-ogy 199210351ndash5633 Vernia P Monteleone G Grandinetti Get al Combined oral sodium butyrate andmesalazine treatment compared to oralmesalazine alone in ulcerative colitis random-ized double-blind placebo-controlled pilotstudy Dig Dis Sci 200045976ndash98134 Di Sabatino A Morera R Ciccocioppo Ret al Oral butyrate for mildly to moderatelyactive Crohnrsquos disease Aliment PharmacolTher 200522789ndash79435 Gao Z Yin J Zhang J et al Butyrate improvesinsulin sensitivity and increases energy expendi-ture in mice Diabetes 2009581509ndash151736 Davie JR Inhibition of histone deacetylaseactivity by butyrate J Nutr 2003133(Suppl)2485Sndash2493S37 Donohoe DR Garge N Zhang X et al Themicrobiome and butyrate regulate energy me-tabolism and autophagy in the mammalian co-lon Cell Metab 201113517ndash52638 Tazoe H Otomo Y Kaji I Tanaka R Karaki S-IKuwahara A Roles of short-chain fatty acids re-ceptors GPR41 and GPR43 on colonic functionsJ Physiol Pharmacol 200859(Suppl 2)251ndash26239 Samuel BS Shaito A Motoike T et al Ef-fects of the gut microbiota on host adiposity aremodulated by the short-chain fatty-acid bindingG protein-coupled receptor Gpr41 Proc NatlAcad Sci U S A 200810516767ndash1677240 Wellen KE Hotamisligil GS Inflammationstress and diabetes J Clin Invest 20051151111ndash111941 Tremaroli V Backhed F Functional interac-tions between the gut microbiota and host me-tabolism Nature 2012489242ndash24942 Cani PD Amar J Iglesias MA et al Meta-bolic endotoxemia initiates obesity and insulinresistance Diabetes 2007561761ndash177243 Delaere F Duchampt AMounien L et al Therole of sodium-coupled glucose co-transporter 3in the satiety effect of portal glucose sensingMolMetab 2012247ndash5344 De Vadder F Kovatcheva-Datchary PGoncalves D et al Microbiota-generated me-tabolites promote metabolic benefits via gut-brain neural circuits Cell 201415684ndash9645 Gill RK Kumar A Malhotra P et al Regula-tion of intestinal serotonin transporter expres-sion via epigenetic mechanisms role of HDAC2Am J Physiol Cell Physiol 2013304C334ndashC34146 Zhu H Huang Q Xu H Niu L Zhou J-NAntidepressant-like effects of sodium butyratein combination with estrogen in rat forcedswimming test involvement of 5-HT(1A) recep-tors Behav Brain Res 2009196200ndash20647 Won Y-J Lu VB Puhl HL 3rd Ikeda SRb-Hydroxybutyrate modulates N-type calciumchannels in rat sympathetic neurons by acting

164 Role of Microbiome in Obesity and T2DM Diabetes Care Volume 38 January 2015

as an agonist for the G-protein-coupled recep-tor FFA3 J Neurosci 20133319314ndash1932548 Basterfield L Mathers JC Intestinal tu-mours colonic butyrate and sleep in exercisedMin mice Br J Nutr 2010104355ndash36349 Yamada T Inui A Hayashi N Fujimura MFujimiya M Serotonin stimulates endotoxintranslocation via 5-HT3 receptors in the rat il-eum Am J Physiol Gastrointest Liver Physiol2003284G782ndashG78850 Simansky KJ Serotonergic control of theorganization of feeding and satiety Behav BrainRes 19967337ndash4251 Ratner C Ettrup A Bueter M et al Cerebralmarkers of the serotonergic system in rat modelsof obesity and after Roux-en-Y gastric bypassObesity (Silver Spring) 2012202133ndash214152 Koopman KE Booij J Fliers E Serlie MJ laFleur SE Diet-induced changes in the leanbrain hypercaloric high-fat-high-sugar snack-ing decreases serotonin transporters in thehuman hypothalamic region Mol Metab20132417ndash42253 Haub S Kanuri G Volynets V Brune TBischoff SC Bergheim I Serotonin reuptaketransporter (SERT) plays a critical role in theonset of fructose-induced hepatic steatosis inmice Am J Physiol Gastrointest Liver Physiol2010298G335ndashG34454 Wikoff WR Anfora AT Liu J et al Metabo-lomics analysis reveals large effects of gut mi-croflora on mammalian blood metabolites ProcNatl Acad Sci U S A 20091063698ndash370355 Romanova IV Ramos EJB Xu Y et al Neuro-biologic changes in the hypothalamus associ-ated with weight loss after gastric bypass JAm Coll Surg 2004199887ndash89556 DefrancescoM Liebaert J Kemmler G et alPsychosocial state after bariatric surgery is as-sociated with the serotonin-transporter

promoter polymorphism Eat Weight Disord201318311ndash31657 Sjostrom L Narbro K Sjostrom CD et alSwedish Obese Subjects Study Effects of bar-iatric surgery on mortality in Swedish obese sub-jects N Engl J Med 2007357741ndash75258 Sjostrom L Lindroos A-K PeltonenM et alSwedish Obese Subjects Study Scientific GroupLifestyle diabetes and cardiovascular risk fac-tors 10 years after bariatric surgery N Engl JMed 20043512683ndash269359 Liou AP Paziuk M Luevano J-M MachineniS Turnbaugh PJ Kaplan LM Conserved shifts inthe gut microbiota due to gastric bypass reducehost weight and adiposity Sci Transl Med 20135178ra4160 Furet J-P Kong L-C Tap J et al Differentialadaptation of human gut microbiota to bariatricsurgery-induced weight loss links with meta-bolic and low-grade inflammation markers Di-abetes 2010593049ndash305761 Zhang H DiBaise JK Zuccolo A et al Humangut microbiota in obesity and after gastric by-pass Proc Natl Acad Sci U S A 20091062365ndash237062 Meyer D Stasse-Wolthuis M The bifido-genic effect of inulin and oligofructose and itsconsequences for gut health Eur J Clin Nutr2009631277ndash128963 Cani PD Neyrinck AM Fava F et al Selec-tive increases of bifidobacteria in gut microfloraimprove high-fat-diet-induced diabetes in micethrough a mechanism associated with endotox-aemia Diabetologia 2007502374ndash238364 Rastall RA Gibson GR Gill HS et al Modu-lation of the microbial ecology of the humancolon by probiotics prebiotics and synbioticsto enhance human health an overview of en-abling science and potential applications FEMSMicrobiol Ecol 200552145ndash152

65 YadavH Jain S SinhaPR Antidiabetic effect ofprobiotic dahi containing Lactobacillus acidophilusand Lactobacillus casei in high fructose fed ratsNutrition 20072362ndash6866 Naito E Yoshida Y Makino K et al Benefi-cial effect of oral administration of Lactobacilluscasei strain Shirota on insulin resistance in diet-induced obesity mice J Appl Microbiol 2011110650ndash65767 Blaser M Antibiotic overuse stop the killingof beneficial bacteria Nature 2011476393ndash39468 Thuny F Richet H Casalta J-P Angelakis EHabib G Raoult D Vancomycin treatment ofinfective endocarditis is linked with recently ac-quired obesity PLoS ONE 20105e907469 Vrieze A Out C Fuentes S et al Impact oforal vancomycin on gut microbiota bile acidmetabolism and insulin sensitivity J Hepatol201460824ndash83170 Dethlefsen L Relman DA Incomplete re-covery and individualized responses of the hu-man distal gut microbiota to repeated antibioticperturbation Proc Natl Acad Sci U S A 2011108(Suppl 1)4554ndash456171 Ajslev TA Andersen CS Gamborg MSoslashrensen TIA Jess T Childhood overweight af-ter establishment of the gutmicrobiota the roleof delivery mode pre-pregnancy weight andearly administration of antibiotics Int J Obes(Lond) 201135522ndash52972 Cho I Yamanishi S Cox L et al Antibiotics inearly life alter the murine colonic microbiomeand adiposity Nature 2012488621ndash62673 Wu GD Chen J Hoffmann C et al Linkinglong-term dietary patterns with gut microbialenterotypes Science 2011334105ndash10874 Cotillard A Kennedy SP Kong LC et al ANRMicroObes consortium Dietary interventionimpact on gut microbial gene richness Nature2013500585ndash588

carediabetesjournalsorg Hartstra and Associates 165

as an agonist for the G-protein-coupled recep-tor FFA3 J Neurosci 20133319314ndash1932548 Basterfield L Mathers JC Intestinal tu-mours colonic butyrate and sleep in exercisedMin mice Br J Nutr 2010104355ndash36349 Yamada T Inui A Hayashi N Fujimura MFujimiya M Serotonin stimulates endotoxintranslocation via 5-HT3 receptors in the rat il-eum Am J Physiol Gastrointest Liver Physiol2003284G782ndashG78850 Simansky KJ Serotonergic control of theorganization of feeding and satiety Behav BrainRes 19967337ndash4251 Ratner C Ettrup A Bueter M et al Cerebralmarkers of the serotonergic system in rat modelsof obesity and after Roux-en-Y gastric bypassObesity (Silver Spring) 2012202133ndash214152 Koopman KE Booij J Fliers E Serlie MJ laFleur SE Diet-induced changes in the leanbrain hypercaloric high-fat-high-sugar snack-ing decreases serotonin transporters in thehuman hypothalamic region Mol Metab20132417ndash42253 Haub S Kanuri G Volynets V Brune TBischoff SC Bergheim I Serotonin reuptaketransporter (SERT) plays a critical role in theonset of fructose-induced hepatic steatosis inmice Am J Physiol Gastrointest Liver Physiol2010298G335ndashG34454 Wikoff WR Anfora AT Liu J et al Metabo-lomics analysis reveals large effects of gut mi-croflora on mammalian blood metabolites ProcNatl Acad Sci U S A 20091063698ndash370355 Romanova IV Ramos EJB Xu Y et al Neuro-biologic changes in the hypothalamus associ-ated with weight loss after gastric bypass JAm Coll Surg 2004199887ndash89556 DefrancescoM Liebaert J Kemmler G et alPsychosocial state after bariatric surgery is as-sociated with the serotonin-transporter

promoter polymorphism Eat Weight Disord201318311ndash31657 Sjostrom L Narbro K Sjostrom CD et alSwedish Obese Subjects Study Effects of bar-iatric surgery on mortality in Swedish obese sub-jects N Engl J Med 2007357741ndash75258 Sjostrom L Lindroos A-K PeltonenM et alSwedish Obese Subjects Study Scientific GroupLifestyle diabetes and cardiovascular risk fac-tors 10 years after bariatric surgery N Engl JMed 20043512683ndash269359 Liou AP Paziuk M Luevano J-M MachineniS Turnbaugh PJ Kaplan LM Conserved shifts inthe gut microbiota due to gastric bypass reducehost weight and adiposity Sci Transl Med 20135178ra4160 Furet J-P Kong L-C Tap J et al Differentialadaptation of human gut microbiota to bariatricsurgery-induced weight loss links with meta-bolic and low-grade inflammation markers Di-abetes 2010593049ndash305761 Zhang H DiBaise JK Zuccolo A et al Humangut microbiota in obesity and after gastric by-pass Proc Natl Acad Sci U S A 20091062365ndash237062 Meyer D Stasse-Wolthuis M The bifido-genic effect of inulin and oligofructose and itsconsequences for gut health Eur J Clin Nutr2009631277ndash128963 Cani PD Neyrinck AM Fava F et al Selec-tive increases of bifidobacteria in gut microfloraimprove high-fat-diet-induced diabetes in micethrough a mechanism associated with endotox-aemia Diabetologia 2007502374ndash238364 Rastall RA Gibson GR Gill HS et al Modu-lation of the microbial ecology of the humancolon by probiotics prebiotics and synbioticsto enhance human health an overview of en-abling science and potential applications FEMSMicrobiol Ecol 200552145ndash152

65 YadavH Jain S SinhaPR Antidiabetic effect ofprobiotic dahi containing Lactobacillus acidophilusand Lactobacillus casei in high fructose fed ratsNutrition 20072362ndash6866 Naito E Yoshida Y Makino K et al Benefi-cial effect of oral administration of Lactobacilluscasei strain Shirota on insulin resistance in diet-induced obesity mice J Appl Microbiol 2011110650ndash65767 Blaser M Antibiotic overuse stop the killingof beneficial bacteria Nature 2011476393ndash39468 Thuny F Richet H Casalta J-P Angelakis EHabib G Raoult D Vancomycin treatment ofinfective endocarditis is linked with recently ac-quired obesity PLoS ONE 20105e907469 Vrieze A Out C Fuentes S et al Impact oforal vancomycin on gut microbiota bile acidmetabolism and insulin sensitivity J Hepatol201460824ndash83170 Dethlefsen L Relman DA Incomplete re-covery and individualized responses of the hu-man distal gut microbiota to repeated antibioticperturbation Proc Natl Acad Sci U S A 2011108(Suppl 1)4554ndash456171 Ajslev TA Andersen CS Gamborg MSoslashrensen TIA Jess T Childhood overweight af-ter establishment of the gutmicrobiota the roleof delivery mode pre-pregnancy weight andearly administration of antibiotics Int J Obes(Lond) 201135522ndash52972 Cho I Yamanishi S Cox L et al Antibiotics inearly life alter the murine colonic microbiomeand adiposity Nature 2012488621ndash62673 Wu GD Chen J Hoffmann C et al Linkinglong-term dietary patterns with gut microbialenterotypes Science 2011334105ndash10874 Cotillard A Kennedy SP Kong LC et al ANRMicroObes consortium Dietary interventionimpact on gut microbial gene richness Nature2013500585ndash588

carediabetesjournalsorg Hartstra and Associates 165