Association of dietary fiber intake and gut microbiota in healthy adults.

This randomized, double-blind, controlled trial evaluated the effects of 4-week dietary fiber supplementation on gut microbiota, bowel-related quality of life, and secondary outcomes, including sleep and skin condition. A total of 105 healthy adults received either low-fiber foods (2.2 g/day total fiber, 1.2 g/day fermentable fiber) or high-fiber foods (8.2 g/day total fiber, including 6.4 g/day fermentable fiber). Gut microbiota was analyzed by 16S rRNA sequencing. Outcomes included stool diary, JPAC-QOL (Japanese version of the Patient Assessment of Constipation Quality of Life), OSA-MA (Oguri-Shirakawa-Azumi sleep inventory MA version), skin questionnaires, and fecal organic acids. The high-fiber group showed significant improvements in JPAC-QOL and increases in SCFA-associated genera such as Anaerostipes, Bifidobacterium, and Fusicatenibacter. These taxa positively correlated with other beneficial bacteria, including Faecalibacterium, suggesting ecological cooperation. The effects on sleep and skin were limited but correlated with beneficial bacteria, implying possible gut–brain and gut–skin axes involvement. This study demonstrated that short-term fiber supplementation meaningfully improved the bowel-related quality of life and beneficially modulated the gut microbiota in healthy adults. Although the systemic effects were modest, microbial shifts suggest that higher fiber intake may provide broader health benefits with longer interventions. This study was registered in the UMIN Clinical Trial Registry (UMIN000054712).

ContextPrior research has explored the effect of synbiotics, the combination of probiotics and prebiotics, on the gut microbiota in clinical populations. However, evidence related to the effect of synbiotics on the gut microbiota in healthy adults has not been reviewed to date.ObjectiveA systematic review and meta-analysis was conducted to comprehensively investigate the effect of synbiotics on the gut microbiota and inflammatory markers in populations of healthy adults.Data SourcesScopus, PubMed, Web of Science, ScienceDirect, MEDLINE, CINAHL, and The Cochrane Library were systematically searched to retrieve randomized controlled trials examining the primary outcome of gut microbiota or intestinal permeability changes after synbiotic consumption in healthy adults. Secondary outcomes of interest were short-chain fatty acids, inflammatory biomarkers, and gut microbiota diversity.Data ExtractionWeighted (WMD) or standardized mean difference (SMD) outcome data were pooled in restricted maximum likelihood models using random effects. Twenty-seven articles reporting on 26 studies met the eligibility criteria (n = 1319).Data AnalysisMeta-analyses of 16 studies showed synbiotics resulted in a significant increase in Lactobacillus cell count (SMD, 0.74; 95% confidence interval [CI], 0.15, 1.33; P = 0.01) and propionate concentration (SMD, 0.22; 95% CI, 0.02, 0.43; P = 0.03) compared with controls. A trend for an increase in Bifidobacterium relative abundance (WMD, 0.97; 95% CI, 0.42, 2.52; P = 0.10) and cell count (SMD, 0.82; 95% CI, 0.13, 1.88; P = 0.06) was seen. No significant differences in α-diversity, acetate, butyrate, zonulin, IL-6, CRP, or endotoxins were observed.ConclusionThis review demonstrates that synbiotics modulate the gut microbiota by increasing Lactobacillus and propionate across various healthy adult populations, and may result in increased Bifidobacterium. Significant variations in synbiotic type, dose, and duration should be considered as limitations when applying findings to clinical practice.Systematic Review RegistrationPROSPERO no. CRD42021284033.

Increasing evidence indicates that gut microbiota may influence colorectal cancer risk. Diet, particularly fibre intake, may modify gut microbiota composition, which may affect cancer risk. We investigated the relationship between dietary fibre intake and gut microbiota in adults. Using 16S rRNA gene sequencing, we assessed gut microbiota in faecal samples from 151 adults in two independent study populations: National Cancer Institute (NCI), n 75, and New York University (NYU), n 76. We calculated energy-adjusted fibre intake based on FFQ. For each study population with adjustment for age, sex, race, BMI and smoking, we evaluated the relationship between fibre intake and gut microbiota community composition and taxon abundance. Total fibre intake was significantly associated with overall microbial community composition in NYU (P=0·008) but not in NCI (P=0·81). In a meta-analysis of both study populations, higher fibre intake tended to be associated with genera of class Clostridia, including higher abundance of SMB53 (fold change (FC)=1·04, P=0·04), Lachnospira (FC=1·03, P=0·05) and Faecalibacterium (FC=1·03, P=0·06), and lower abundance of Actinomyces (FC=0·95, P=0·002), Odoribacter (FC=0·95, P=0·03) and Oscillospira (FC=0·96, P=0·06). A species-level meta-analysis showed that higher fibre intake was marginally associated with greater abundance of Faecalibacterium prausnitzii (FC=1·03, P=0·07) and lower abundance of Eubacterium dolichum (FC=0·96, P=0·04) and Bacteroides uniformis (FC=0·97, P=0·05). Thus, dietary fibre intake may impact gut microbiota composition, particularly class Clostridia, and may favour putatively beneficial bacteria such as F. prausnitzii. These findings warrant further understanding of diet-microbiota relationships for future development of colorectal cancer prevention strategies.

This study aimed to detect dietary fiber intake and its association with nonfatal cardiovascular/cerebrovascular events (myocardial infarction and stroke) in adults in the United States. This cross-sectional study obtained data from the 2011–2018 National Health and Nutrition Examination Survey database. Using multivariate logistic regression, we compared dietary fiber intake across demographics and detected an association between dietary fiber intake and patient-reported nonfatal myocardial infarction and/or stroke events. We enrolled 8,872 participants (mean dietary fiber intake, 17.38 ± 0.22 g/day). The weighted prevalence of nonfatal cardiovascular/cerebrovascular events was 5.36%, which decreased with higher dietary fiber intake (nonfatal cardiovascular/cerebrovascular events: Tertile1, 6.50%; Tertile2, 5.45%; Tertile3, 4.25%). Higher fiber intake indicated a stable negative association with nonfatal cardiovascular/cerebrovascular events in the multivariate logistic regression analysis, weighted generalized additive model, and smooth curve fitting. Interaction tests showed no significant effect of demographic, socioeconomic, and disease status on the association between dietary fiber intake and nonfatal cardiovascular/cerebrovascular events. Dietary fiber intake was far below the recommended amount. Higher dietary fiber intake was associated with a lower prevalence of nonfatal cardiovascular/cerebrovascular events.

Introduction: Emerging evidence suggesting diabetes -protective effects of dietary fiber intake. However, the underlying mechanisms are not fully understood. Hypothesis: We hypothesize that higher dietary fiber intake can alter gut microbial composition /functional capacity and host circulating metabolomic profile, which may contribute to lower risk of diabetes. Methods: We evaluated the associations of dietary fiber intake with gut microbiome (measured by shotgun metagenomic sequencing, n=2959) and serum metabolome (639 metabolites measured by untargeted metabolomic approach, n=6198) in the HCHS/SOL cohort. We further examined prospective associations of baseline fiber/microbial-associated metabolites with incident diabetes over 6-years follow-up. Results: We identified 39 bacterial genera associated with fiber intake, after adjustment for sociodemographic, behavioral, and clinical factors. 12 of these fiber-associated genera were related with diabetes (e.g. the fiber-associated Roseburia was inversely associated with diabetes, Fig.1A ). We identified 83 fiber-associated metabolites which were clustered into 13 modules in network, 7 of which were significantly associated with risk of diabetes ( Fig.1B ). Some of these diabetes-associated metabolite modules were also associated with fiber/diabetes-associated bacterial taxa ( Fig.1C ). In particular, indolepropionate module, and another module comprised of the pro-vitamins such as beta-cryptoxanthin, were positively associated with fiber (all P<0.001) and inversely associated with diabetes risk (RR [95% CI] = 0.78[0.69, 0.89] and 0.83[0.72, 0.94] respectively), and both associated with the fiber-degradation genera Butyrivibrio (P<0.001). Conclusion: Among US Hispanics/Latinos, higher fiber intake was associated with favorable profiles of gut microbiota and circulating metabolites for diabetes, suggesting a potential role of gut microbiota and related metabolites in the link between dietary fiber intake and risk of diabetes.

Effect of chicory inulin-type fructan–containing snack bars on the human gut microbiota in low dietary fiber consumers in a randomized crossover trial

A low-fibre diet leads to gut microbiota imbalance, characterized by low diversity and reduced ability to produce beneficial metabolites, such as short-chain fatty acids (SCFAs). This imbalance is associated with poor gastrointestinal and metabolic health. We aimed to determine whether one dietary change, substitution of white bread with high-fibre bread, improves gut microbiota diversity and SCFA-producing capability. Twenty-two healthy adults completed a two-phase randomized, cross-over trial. The participants consumed three slices of a high-fibre bread (Prebiotic Cape Seed Loaf with BARLEYmax®) or control white bread as part of their usual diet for 2 weeks, with the treatment periods separated by a 4-week washout. High-fibre bread consumption increased total dietary fibre intake to 40 g/d, which was double the amount of fibre consumed at baseline or during the white bread intervention. Compared to white bread, the high-fibre bread intervention resulted in higher faecal alpha diversity (Shannon, p = 0.014) and relative abundance of the Lachnospiracae ND3007 group (p < 0.001, FDR = 0.019) and tended to increase the butyrate-producing capability (p = 0.062). In conclusion, substituting white bread with a high-fibre bread improved the diversity of gut microbiota and specific microbes involved in SCFA production and may enhance the butyrate-producing capability of gut microbiota in healthy adults. These findings suggest that a single dietary change involving high-fibre bread provides a practical way for adults to exceed recommended dietary fibre intake levels that improve gut microbiota composition and support gastrointestinal and metabolic health.

High-fiber diet and rope-skipping benefit cardiometabolic health and modulate gut microbiota in young adults: A randomized controlled trial

The intestinal microbiota is a crucial regulator of human health and disease because of its interactions with the immune system. Tobacco smoke also influences the human ecosystem with implications for disease development. This systematic review aims to analyze the available evidence, until June 2021, on the relationship between traditional and/or electronic cigarette smoking and intestinal microbiota in healthy human adults. Of the 2645 articles published in PubMed, Scopus, and Web of Science, 13 were included in the review. Despite differences in design, quality, and participants’ characteristics, most of the studies reported a reduction in bacterial species diversity, and decreased variability indices in smokers’ fecal samples. At the phylum or genus level, the results are very mixed on bacterial abundance both in smokers and non-smokers with two exceptions. Prevotella spp. appears significantly increased in smokers and former smokers but not in electronic cigarette users, while Proteobacteria showed a progressive increase in Desulfovibrio with the number of pack-years of cigarette (p = 0.001) and an increase in Alphaproteobacteria (p = 0.04) in current versus never smokers. This attempt to systematically characterize the effects of tobacco smoking on the composition of gut microbiota gives new perspectives on future research in smoking cessation and on a new possible use of probiotics to contrast smoke-related dysbiosis.

Prostate cancer is one of the most common cancers in the United States. Dietary fiber intake may play a role in reducing cancer risk and mortality. However, the relationship between dietary fiber intake and both prostate cancer risk and prostate cancer-specific mortality remains uncertain. The aim of the study was to examine the association between dietary fiber intake and prostate cancer risk, prostate cancer-specific mortality, and all-cause mortality. This study was a secondary analysis of the Prostate, Lung, Colorectal, and Ovarian Cancer Screening Study, a multicenter randomized trial conducted in the United States that included 2 arms: one undergoing annual screening and the other receiving usual care. A total of 49 476 participants (annual screening arm: 25 669 men; usual care arm: 23 807 men) aged 55 to 74 years were enrolled from the Prostate, Lung, Colorectal, and Ovarian Cancer Screening Study between the years 1993 and 2001. Prostate cancer risk, prostate cancer-specific mortality, and all-cause mortality were considered as main outcomes. Cox proportional hazard and competing risk regressions were used within each arm to examine the associations of dietary fiber intake with prostate cancer risk, all-cause mortality, and prostate cancer-specific mortality. Compared with the low tertile total fiber intake, high tertile total fiber intake in the annual screening arm was linked to reduced prostate cancer risk (adjusted hazard ratio 0.87; 95% CI, 0.76 to 0.99), and high-soluble fiber intake in the usual care arm had a similar association (adjusted hazard ratio 0.86; 95% CI, 0.75 to 0.98) after adjusting for confounders. There were statistically significant inverse associations between dietary fiber intake (total, insoluble, and soluble) and all-cause mortality among participants in both arms (P < .01). Significant associations of dietary fiber intake (total, soluble, and insoluble) with advanced prostate cancer risk and prostate cancer-specific mortality in both arms were not observed (P > .05). High dietary fiber intake (total, soluble, and insoluble) was found to be associated with decreased all-cause mortality, which may suggest a protective effect of dietary fiber intake. Further prospective studies are needed to build on these findings.

BackgroundLow dietary fiber intake is common in the US, despite its health benefits. Individuals with metabolic syndrome (MetS), at high cardiovascular risk, may benefit significantly from higher fiber, but its link to mortality in this group is unclear.MethodsWe analyzed prospective data from 10,962 U.S. adults with MetS (NHANES 1999–2018, mean age 58.1). Baseline fiber intake (g/day) was assessed via 24-h recalls. MetS was defined by ATP III criteria. Mortality (all-cause, CVD-specific) was tracked via the National Death Index (median follow-up 102 months). Cox models estimated hazard ratios (HRs) for mortality associated with fiber intake, adjusted for demographics, socioeconomic status, lifestyle, and comorbidities.ResultsOver follow-up, 2,617 deaths occurred (887 CVD-specific). Higher fiber intake was associated with significantly lower mortality. Our analysis suggested a potential threshold effect near 21.7 g/day of fiber intake. Below this, each additional 5 g fiber reduced all-cause mortality risk by 7% (HR = 0.93, 95% CI: 0.91–0.96, p < 0.0001). Comparing highest to lowest tertile intake, adjusted HRs were 0.80 (95% CI 0.72–0.89, p < 0.0001) for all-cause and 0.61 (0.51–0.73, p < 0.0001) for CVD mortality. Results were robust in sensitivity analyses.ConclusionIn U.S. adults with MetS, higher dietary fiber intake was associated with significantly lower all-cause and CVD mortality. Benefits were most pronounced at lower intakes, plateauing around 22 g/day, suggesting achieving moderate fiber intake near recommendations offers substantial survival benefits in this high-risk group.

High dietary fiber intake is associated with decreased inflammation and all-cause mortality in patients with chronic kidney disease

Simple SummaryHigh dietary fiber intake has been linked to a lower risk of Colorectal cancer (CRC), but the role of dietary fiber in CRC survival is understudied. We examined dietary fiber intake for its relevance to CRC survival in a cohort of 504 CRC patients and a meta-analysis including results from four prospective cohort studies. We found that high dietary fiber intake was negatively correlated with all-cause mortality and CRC-specific mortality among CRC survivors. These new findings support the protective effect of dietary fiber on CRC survival. By enhancing fiber intake, this research may contribute to the development of novel therapies that add to our armamentarium for CRC.We examined dietary fiber intake for its relevance to Colorectal cancer (CRC) survival in a cohort of CRC patients and a meta-analysis including results from four prospective cohort studies. We analyzed 504 CRC patients enrolled in the Newfoundland Familial Colorectal Cancer Study (NFCCS) who were newly diagnosed with CRC between 1999 and 2003. Follow-up for deaths was through April 2010. All participants completed a self-administered food frequency questionnaire to evaluate their dietary intakes one year before diagnosis. Multivariable Cox proportional hazard models were used to explore the associations of dietary fiber intake with all-cause mortality and CRC-specific mortality. In the meta-analysis, we identified prospective cohort studies published between January 1991 and December 2021 by searching PubMed, EMBASE, and Cochrane Library. Fixed-effects or random-effects models were used to combine the study-specific hazard ratio (HR) from our original analysis and three other cohorts. In the NFCCS, we found that CRC patients with the second quartile of dietary fiber intake had a 42% lower risk of all-cause mortality (HR: 0.58, 95% CI: 0.35–0.98) and 58% lower risk of CRC-specific mortality (HR: 0.42, 95% CI: 0.21–0.87) compared with those with the lowest quartile. In the meta-analysis, a similar inverse association between dietary fiber and total mortality was detected among CRC patients; each 10 g/day increase in dietary fiber intake was associated with a 16% decreased risk of total mortality. The dose–response meta-analysis showed a linear relationship between dietary fiber intake and all-cause mortality, with no sign of a plateau. For CRC-specific mortality, intriguingly, the benefit associated with increasing dietary fiber intake achieved its maximum at approximately 22 g/day, and no further reduction in CRC-specific mortality was observed beyond this intake level. Our results suggest that high dietary fiber intake may be associated with prolonged survival among CRC patients. Our findings add to the sparse literature on the role of dietary fiber in CRC survival.

A prospective analysis of dietary fiber intake and mental health quality of life in the Iowa Women’s Health Study

Background Findings of previous studies on relationship between dietary fiber intake and depression were inconsistent. We performed a meta-analysis on the association of dietary fiber intake with depression and anxiety in epidemiologic studies. Methods We conducted a systematic search of electronic databases, up to May 2021. Data from 18 publications (12 cross-sectional, five cohort and one case–control studies) on dietary fiber consumption in relation to depression or anxiety were included. For depression, fifteen studies were conducted on adults and three others on adolescents. Anxiety was not included in the analysis, due to insufficient eligible studies. Results Total dietary fiber intake was associated with a 10% lower odds of depression (OR = 0.90; 95% confidence interval [CI]: 0.86, 0.95) in adults and a 57% lower odds (OR = 0.43, 95% CI: 0.32, 0.59) in adolescents. Dose–response meta-analysis revealed an inverse linear association between total dietary fiber intake and odd of depression in adults; such that each 5-g increase in total dietary fiber intake was associated with a 5% reduction in risk of depression (OR = 0.95; 95% CI: 0.94, 0.97). An inverse significant association was observed between intake of fiber from vegetables (OR = 0.73; 95% CI: 0.66, 0.82) and soluble fiber (OR = 0.80, 95% CI: 0.71, 0.91) and odds of depression. However, cereal fiber, fiber from fruits and insoluble fiber were marginally associated with a reduction in having depression. Conclusions High intake of dietary fiber was protectively associated with depression in adults, in a dose–response fashion.