Caloric Restriction, Friend or Foe: Effects on Metabolic Status in Association with the Intestinal Microbiome and Metabolome

The Obesity-Epigenetics-Microbiome Axis: Strategies for Therapeutic Intervention

Obesity (OB) has become a serious health issue owing to its ever-increasing prevalence over the past few decades due to its contribution to severe metabolic and inflammatory disorders such as cardiovascular disease, type 2 diabetes, and cancer. The unbalanced energy metabolism in OB is associated with substantial epigenetic changes mediated by the gut microbiome (GM) structure and composition alterations. Remarkably, experimental evidence also indicates that OB-induced epigenetic modifications in adipocytes can lead to cellular "memory" alterations, predisposing individuals to weight regain after caloric restriction and subsequently inducing inflammatory pathways in the liver. Various environmental factors, especially diet, play key roles in the progression or prevention of OB and OB-related disorders by modulating the GM structure and composition and affecting epigenetic mechanisms. Here, we will first focus on the key role of epigenetic aberrations in the development of OB. Then, we discuss the association between abnormal alterations in the composition of the microbiome and OB and the interplays between the microbiome and the epigenome in the development of OB. Finally, we review promising strategies, including prebiotics, probiotics, a methyl-rich diet, polyphenols, and herbal foods for the prevention and/or treatment of OB via modulating the GM and their metabolites influencing the epigenome.

Intermittent fasting applied in combination with astaxanthin alleviates D-galactose-induced aging in rats: Comparison in oxidative stress, immune response, and metabolomics

Effective anti-aging strategies involving dietary restriction and antioxidant supplementation are gaining increasing research attention, while the health effects of their combined intervention are rarely reported. In this study, for the first time, we investigated the anti-aging effects and underlying mechanisms of intermittent fasting (IF), astaxanthin (AX), and their combination in D-galactose-induced aging rats. Our results demonstrated that these three treatments effectively inhibited malondialdehyde levels and improved the activity of endogenous antioxidant enzymes in the brain, liver, and serum of aging rats. Simultaneously, the combination of IF and AX had a synergistic effect on the recovery of brain mitochondrial injury as evidenced by permeability transition pore openness, membrane potential, respiratory chain complex enzyme activity, and cortical and hippocampal lesions. Notably, the combination significantly increased the levels of Immunoglobulin M (55.66 ± 3.23%), immunoglobulin G (34.41 ± 2.65%), and IL-2 (23.49 ± 1.78%) compared with the model group. Moreover, AX reduced the accumulation of pro-inflammatory factor IL-6 (23.06 ± 2.02%), while the combination induced more remarkable reduction in the accumulation of IL-1β (35.92 ± 3.06%) in the serum. Considering the serum metabolomics analysis, we hypothesized that IF and AX played a positive role in the regulation of the nervous system, which was associated with the differential metabolites lysope 16:0, N-Acety-L-tyrosine, and L-Alanyl-L-Lysine. This research reveals that the combination therapy provided synergistic anti-aging efficacy by enhancing resistance to oxidative stress, ameliorating mitochondrial dysfunction, and restoring the immune system. These findings might have significant implications for further studies on the exploration of effective anti-aging therapy.

Cellulose-like chitosan microfibrils facilitate targeted release and enhance the prolonged residence time of quercetin-selenium nanoparticles for Alzheimer's disease treatment

The effect of digestion on nanocarriers will affect the release and pharmacological effects of bioactive compounds in delivery systems. The digestion of cellulose is limited to gut microbiota, which offers a new research strategy for targeted delivery of bioactive compounds. Herein, positively charged cellulose-like chitosan/polyvinylpyrrolidone nanofiber was prepared to improve the residence time, colon target and gut microbiota regulation activity of quercetin decorated selenium nanoparticles (QUE@SeNPs/CS/PVPNFs). Selenium nanoparticles block the degradation of quercetin and QUE@SeNPs/CS/PVPNFs only decompose when caused by chitosanase secretion from gut microbiota. In vivo imaging showed that the residence time of QUE@SeNPs/CS/PVPNFs was longer than that of QUE@SeNPs. Thus, it significantly decreased the lipid concentrations in liver, which further inhibited insulin resistance in mice. Moreover, QUE@SeNPs/CS/PVPNFs treatment improves gut barrier integrity, increased the relative abundance of anti-obesity and anti-inflammation related bacterial including Akkermansia, Lactobacillus and Bacteroides. Consequently, the inflammatory factor (IL-β and TNF-α) levels in gut, liver and brain were also decreased. Nissl and PSD-95 staining indicated that QUE@SeNPs/CS/PVPNFs ameliorated synapse dysfunction in the brain. Therefore, QUE@SeNPs/CS/PVPNFs has a greater effect than QUE@SeNPs in improving cognitive ability in Morris water maze. Overall, QUE@SeNPs/CS/PVPNFs with prolonged residence time attenuates cognitive disorder via gut-liver-brain axis in AD.

Caloric Restriction Preserves BBB Integrity After Transient Focal Cerebral Ischemia Through Reducing Neutrophil Infiltration

AIMS

Caloric restriction is a health-promoting lifestyle that has been reported to protect both white and gray matter in cases of ischemic stroke. This study will explore the underlying mechanism of restricted feeding (RF) and provide a theoretical basis for precise clinical treatment of stroke.

METHODS

In this study, we pretreated C57BL/6J mice with 70% RF for a continuous 28-day period prior to 60 min of transient focal cerebral ischemia (tFCI). Histological staining, diffusion tensor imaging (DTI), and behavioral assessments were used to assess RF's neuroprotection following tFCI. Immunofluorescence staining, quantitative real-time PCR, and flow cytometry were conducted to evaluate brain inflammation post-tFCI. Western blot, immunofluorescence staining, tracers, and electric microscopy were used to assess the blood-brain barrier (BBB) integrity. Peripheral neutrophils were cleared by administrating an anti-Ly6G antibody.

RESULTS

Initially, DTI, NeuN staining, and a batch of behavioral tests verified that RF significantly mitigated both gray/white matter injury and neurological deficits in the short- and long-term following tFCI. RF mice showed more anti-inflammatory microglia in their brains, along with reduced inflammatory cytokines, and chemokines. Interestingly, RF significantly reduced the neutrophils and macrophage infiltration. Subsequently, we observed that RF mice exhibited better BBB integrity following tFCI, with reduced neutrophil infiltration and matrix metalloprotein-9 release. Furthermore, the clearance of neutrophils with anti-Ly6G antibody in ad libitum feeding mice (LF-Ly6G) elicited comparable neuroprotective effects to those observed in RF, including improvements in neurological deficits, reductions in infarct volume, and mitigation of BBB damage.

CONCLUSIONS

In summary, our findings suggest that RF maintains the BBB integrity following ischemic stroke at least partially by reducing neutrophil infiltration, thereby alleviating both neurological and histological impairments.

Feed restriction as a model for small intestinal permeability in nursery pigs

Reduced feed intake is a hallmark of many animal diseases and environmental conditions and has been shown to cause intestinal barrier dysfunction. As there are several markers and assays to evaluate intestinal barrier function, feed restriction may present a potential model to validate and compare multiple in vivo, ex vivo, and tissue markers of intestinal integrity. Forty-eight barrows (9.7 kg initial body weight) were fed for 7 d at feed intakes of 100%, 75%, 50%, or 25% of expected ad libitum feed intake. After which urine, and blood were taken for in vivo lactulose:mannitol analysis. Additional ileum samples were taken for examination of intestinal function including ex vivo tissue transepithelial electrical resistance (TEER), tissue fluorescein isothiocyanate-dextran (FD4) transport, as well as small intestinal villus height and crypt depth, and gene expression. Data were analyzed as an ANOVA as well as a contrast where 25% and 50% were combined, as were 75% and 100%. As expected, observed feed intake followed a linear pattern, as did body weight changes. Pigs fed ad libitum (100%) gained 3.8 kg whereas pigs fed at 75% restriction gained 2.5 kg, pigs fed at 50% restriction gained 1.2 kg and pigs fed at 25% lost 0.37 kg (P < 0.05). Results showed tissue changes in morphology in duodenum, jejunum and ileum at 25% and 50% feed restriction (P < 0.05). Specifically, pigs fed at 75% and 100% feed levels had on average a 26% greater villus height compared to pigs fed at 50% and 25% (P < 0.01). There were no significant differences in TEER, however there was also a tendency for a contrast difference for FD4 as well as for a significant increase in urinary lactulose:mannitol at 25% compared to 75% and 100% (P < 0.10). Similarly, pro-inflammatory gene marker, IL17A was increased at 25% feeding level compared to 75% and 100% (P < 0.05). Taken together, these data show that feed restriction may be a good model to compare validation methods for intestinal permeability and function, but that length of feed restriction may have reduced larger impacts on intestinal function observed in other studies.

Development of a malnutrition model in mice: Comparative evaluation of food restriction percentage and different diets

Malnutrition is a complicated illness that affects people worldwide and is linked to higher death rates, a heightened vulnerability to infections, and delayed cognitive development. Experimental models have been constructed to comprehend the mechanisms associated with hunger. In this regard, the current study used two different types of food aiming to validate a murine model of malnutrition based on dietary restriction. The study was conducted with fifty-six Swiss male mice (eight-week-old) divided into eight groups (n=7 each) and fed the following experimental diets (10 weeks): Standard Diet (ST) ad libitum; ST 20% dietary restriction; ST 40% dietary restriction; ST 60% dietary restriction; AIN93-M diet ad libitum; AIN93-M 20% dietary restriction; AIN93-M 40% dietary restriction; AIN93-M 60% dietary restriction. Body, biochemical, and histological parameters were measured, and the restriction effects on genes related to oxidative stress (GPX1 and GPX4) in epididymal adipose tissue were evaluated. The results obtained showed that 20%, 40%, and 60% of dietary restrictions were able to reduce body weight when compared to controls, highlighting the accentuated weight loss in animals with 60% restrictions, especially those fed with AIN-93 M, which showed physical changes such as whitish skin and dull coat, voracious eating, and hunched posture. The present animal model also showed biochemical changes with hypoalbuminemia, as well as histological epididymal adipose tissue modulation. The presence of increased oxidative stress was observed when evaluating the GPX4 gene. Given the results, 60% food restriction using the AIN93-M diet was the best protocol for inducing malnutrition.

The role of intestinal microbiota in physiologic and body compositional changes that accompany CLA-mediated weight loss in obese mice

OBJECTIVE

Obesity continues to be a major problem, despite known treatment strategies such as lifestyle modifications, pharmaceuticals, and surgical options, necessitating the development of novel weight loss approaches. The naturally occurring fatty acid, 10,12 conjugated linoleic acid (10,12 CLA), promotes weight loss by increasing fat oxidation and browning of white adipose tissue, leading to increased energy expenditure in obese mice. Coincident with weight loss, 10,12 CLA also alters the murine gut microbiota by enriching for microbes that produce short chain fatty acids (SCFAs), with concurrent elevations in fecal butyrate and plasma acetate.

METHODS

To determine if the observed microbiota changes are required for 10,12 CLA-mediated weight loss, adult male mice with diet-induced obesity were given broad-spectrum antibiotics (ABX) to perturb the microbiota prior to and during 10,12 CLA-mediated weight loss. Conversely, to determine whether gut microbes were sufficient to induce weight loss, conventionally-raised and germ-free mice were transplanted with cecal contents from mice that had undergone weight loss by 10,12 CLA supplementation.

RESULTS

While body weight was minimally modulated by ABX-mediated perturbation of gut bacterial populations, adult male mice given ABX were more resistant to the increased energy expenditure and fat loss that are induced by 10,12 CLA supplementation. Transplanting cecal contents from donor mice losing weight due to oral 10,12 CLA consumption into conventional or germ-free mice led to improved glucose metabolism with increased butyrate production.

CONCLUSIONS

These data suggest a critical role for the microbiota in diet-modulated changes in energy balance and glucose metabolism, and distinguish the metabolic effects of orally delivered 10,12 CLA from cecal transplantation of the resulting microbiota.

Unveiling the causal effects of gut microbiome on trimethylamine N-oxide: evidence from Mendelian randomization

Objective

The relationship between gut microbiome and trimethylamine oxide (TMAO) has not been fully elucidated. We aimed to assess the causal effects of different gut microbes on TMAO using Mendelian randomization (MR).

Methods

Gut microbiome and TMAO datasets were acquired from genome-wide association studies and screened for single nucleotide polymorphisms according to the basic assumptions of MR. Inverse variance weighted was used as the main method in MR analysis to assess the causal relationship between the gut microbiome and TMAO. Finally, the MR-Egger intercept, Cochran's Q test, and leave-one-out sensitivity analysis were used to assess the horizontal pleiotropy, heterogeneity, and robustness of the results, respectively.

Results

MR analysis revealed that the species Bacteroides finegoldii (odds ratio [OR] 1.064, 95% confidence interval [CI] 1.003 to 1.128, p = 0.039), family Sutterellaceae (OR 1.188, 95% CI 1.003 to 1.407, p = 0.047), and phylum Pseudomonadota (OR 1.205, 95% CI 1.036 to 1.401, p = 0.016), as well as the species Bacteroides uniformis (OR 1.263, 95% CI 1.039 to 1.535, p = 0.019), were positively associated with increased genetic susceptibility to TMAO. In contrast, the species Bacteroides thetaiotaomicron (OR 0.813, 95% CI 0.696 to 0.950, p = 0.009) and Bilophila wadsworthia (OR 0.828, 95% CI 0.690 to 0.995, p = 0.044) were associated with reduced genetic susceptibility to TMAO. Additionally, the MR-Egger intercept indicated no horizontal pleiotropy (p ≥ 0.05), and Cochran's Q test and sensitivity analysis demonstrated that the results were not heterogeneous (p ≥ 0.05) and were robust.

Conclusion

Our findings revealed the role of the phylum Pseudomonadota, family Sutterellaceae, species Bacteroides finegoldii, and Bacteroides uniformis in increasing TMAO, as well as the species Bacteroides thetaiotaomicron and Bilophila wadsworthia in decreasing TMAO. This study provides new insights into the relationship between the gut microbiome and TMAO levels.

The Effects of Caloric Restriction and Clinical Psychological Intervention on the Interplay of Gut Microbial Composition and Stress in Women

Both mental and metabolic disorders are steadily becoming more prevalent, increasing interest in non-pharmacological lifestyle interventions targeting both types of disorders. However, the combined effect of diet and psychological interventions on the gut microbiome and mental health outcomes remains underexplored. Thus, in this study, we randomized 41 women into two caloric restriction (CR) dietary groups, namely very-low-calorie diet (VLCD) and F.X. Mayr diet (FXM). The patients were then further randomized to either receive clinical psychological intervention (CPI) or no CPI. Blood and fecal samples were collected before and after two weeks of CR. Psychometric outcomes were assessed using the Perceived Stress Scale (PSS), Brief Symptom Index (BSI), and Burnout Dimension Inventory (BODI). Stool samples underwent 16S-rRNA sequencing. Upon two weeks of CR, α-diversity decreased overall and longitudinal PERMANOVA models revealed significant shifts in β-diversity according to diet, CPI, age, and body-mass-index. Furthermore, Agathobacter, Fusicatenibacter, and Subdoligranulum decreased in abundance. However, the Oscillibacter genus was enriched solely in FXM. CPI had a negligible effect on the microbiome. Dimension reduction models revealed clusters of taxa which distinctly associated with psychometric outcomes. Members of the Oscillospiraceae family were linked to favorable psychometric outcomes after two weeks of CR. Despite α-diversity reductions after CR, enrichment of Oscillospiraceae spp., solely seen in FXM, correlated with improved psychometric outcomes. This study suggests a promising direction for future interventions targeting mental health through gut microbial modulation.

Intermittent fasting, exercise, and dietary modification induce unique transcriptomic signatures of multiple tissues governing metabolic homeostasis during weight loss and rebound weight gain

Obesity and its related metabolic diseases bring great challenges to public health. In-depth understanding on the efficacy of weight-loss interventions is critical for long-term weight control. Our study demonstrated the comparable efficacy of exercise (EX), intermittent fasting (IF), or the change of daily diet from an unhealthy to a normal chow (DR) for weight reduction, but largely divergently affected metabolic status and transcriptome of subcutaneous fat, scapular brown fat, skeletal muscles and liver in high-fat-high-fructose diet (HFHF) induced obese mice. EX and IF reduced systematic inflammation, improved glucose and lipid metabolism in liver and muscle, and amino acid metabolism and thermogenesis in adipose tissues. EX exhibited broad regulatory effects on TCA cycle, carbon metabolism, thermogenesis, propanoate-, fatty acid and amino acid metabolism across multiple tissues. IF prominently affected genes involved in mitophagy and autophagy in adipose tissues and core genes involved in butanoate metabolism in liver. DR, however, failed to improve metabolic homeostasis and biological dysfunctions in obese mice. Notably, by exploring potential inter-organ communication, we identified an obesity-resistant-like gene profile that were strongly correlated with HFHF induced metabolic derangements and could predict the degree of weight regain induced by the follow-up HFHF diet. Among them, 12 genes (e.g., Gdf15, Tfrc, Cdv3, Map2k4, and Nqo1) were causally associated with human metabolic traits, i.e., BMI, body fat mass, HbA1C, fasting glucose, and cholesterol. Our findings provide critical groundwork for improved understanding of the impacts of weight-loss interventions on host metabolism. The identified genes predicting weight regain may be considered regulatory targets for improving long-term weight control.

Early-life stress and the gut microbiome: A comprehensive population-based investigation

Early-life stress (ELS) has been robustly associated with a range of poor mental and physical health outcomes. Recent studies implicate the gut microbiome in stress-related mental, cardio-metabolic and immune health problems, but research on humans is scarce and thus far often based on small, selected samples, often using retrospective reports of ELS. We examined associations between ELS and the human gut microbiome in a large, population-based study of children. ELS was measured prospectively from birth to 10 years of age in 2,004 children from the Generation R Study. We studied overall ELS, as well as unique effects of five different ELS domains, including life events, contextual risk, parental risk, interpersonal risk, and direct victimization. Stool microbiome was assessed using 16S rRNA sequencing at age 10 years and data were analyzed at multiple levels (i.e. α- and β-diversity indices, individual genera and predicted functional pathways). In addition, we explored potential mediators of ELS-microbiome associations, including diet at age 8 and body mass index at 10 years. While no associations were observed between overall ELS (composite score of five domains) and the microbiome after multiple testing correction, contextual risk - a specific ELS domain related to socio-economic stress, including risk factors such as financial difficulties and low maternal education - was significantly associated with microbiome variability. This ELS domain was associated with lower α-diversity, with β-diversity, and with predicted functional pathways involved, amongst others, in tryptophan biosynthesis. These associations were in part mediated by overall diet quality, a pro-inflammatory diet, fiber intake, and body mass index (BMI). These results suggest that stress related to socio-economic adversity - but not overall early life stress - is associated with a less diverse microbiome in the general population, and that this association may in part be explained by poorer diet and higher BMI. Future research is needed to test causality and to establish whether modifiable factors such as diet could be used to mitigate the negative effects of socio-economic adversity on the microbiome and related health consequences.

Oat-based postbiotics ameliorate high-sucrose induced liver injury and colitis susceptibility by modulating fatty acids metabolism and gut microbiota

High-sucrose (HS) consumption leads to metabolic disorders and increases susceptibility to colitis. Postbiotics hold great potentials in combating metabolic diseases and offer advantages in safety and processability, compared with living probiotics. We developed innovative oat-based postbiotics and extensively explored how they could benefit in rats with long-term high-sucrose consumption. The postbiotics fermented with Lactiplantibacillus plantarum (OF-1) and OF-5, the one fermented with the optimal selection of five probiotics (i.e., L. plantarum, Limosilactobacillus reuteri, Lacticaseibacillus rhamnosus, Lactobacillus acidophilus, and Bifidobacterium lactis) alleviated HS induced liver injury, impaired fatty acid metabolism and inflammation through activating AMPK/SREBP-1c pathways. Moreover, oat-based postbiotics restored detrimental effects of HS on fatty acid profiles in liver, as evidenced by the increases in polyunsaturated fatty acids and decreases in saturated fatty acids, with OF-5 showing most pronounced effects. Furthermore, oat-based postbiotics prevented HS exacerbated susceptibility to dextran sodium sulfate caused colitis and reconstructed epithelial tight junction proteins in colons. Oat-based postbiotics, in particular OF-5 notably remodeled gut microbiota composition, e.g., enriching the relative abundances of Akkermansia, Bifidobacterium, Alloprevotella and Prevotella, which may play an important role in the liver-colon axis responsible for improvements of liver functions and reduction of colitis susceptibility. The heat-inactivated probiotics protected against HS-induced liver and colon damage, but such effects were less pronounced compared with oat-based postbiotics. Our findings emphasize the great value of oat-based postbiotics as nutritional therapeutics to combat unhealthy diet induced metabolic dysfunctions.

A Novel Plant-Based Nutraceutical Combined with Exercise Can Revert Oxidative Status in Plasma and Liver in a Diet-Induced-Obesity Animal Model

The prevalence of obesity increases alarmingly every year mostly due to external factors such as high-fat and high-refined sugar intake associated with a sedentary lifestyle. It triggers metabolic disorders such as insulin resistance, hyperlipemia, non-alcoholic fatty liver disease, chronic inflammation, oxidative stress, and gut microbiota dysbiosis. The aim of this study was to evaluate the beneficial effects of a combined intervention with caloric restriction, nutraceutical intake, and a mixed training protocol on oxidative stress, inflammation, and gut dysbiosis derived from the development of obesity in a C57BL6/J mouse experimental model of diet-induced obesity (4.6 Kcal/g diet, 45% Kcal as fat, and 20% fructose in the drinking fluid). The nutraceutical was formulated with ethanolic extracts of Argania spinosa pulp (10%) and Camelina sativa seeds (10%) and with protein hydrolysates from Psoralea corylifolia seeds (40%) and Spirodela polyrhiza whole plants (40%). The combination of nutraceutical and exercise decreased the animals' body weights and inflammatory markers (TNFα, IL-6, and resistin) in plasma, while increasing gene expression of cat, sod2, gsta2, and nqo1 in the liver. Obese animals showed lower β-diversity of microbiota and a higher Firmicutes/Bacteroidetes ratio vs. normocaloric controls that were reversed by all interventions implemented. Dietary inclusion of a nutraceutical with high antioxidant potential combined with an exercise protocol can be beneficial for bodyweight control and improvement of metabolic status in patients undergoing obesity treatment.

Remodelling of the intestinal ecosystem during caloric restriction and fasting

Benefits of fasting and caloric restriction on host metabolic health are well established, but less is known about the effects on the gut microbiome and how this impacts renewal of the intestinal mucosa. What has been repeatedly shown during fasting, however, is that bacteria utilising host-derived substrates proliferate at the expense of those relying on dietary substrates. Considering the increased recognition of the gut microbiome's role in maintaining host (metabolic) health, disentangling host-microbe interactions and establishing their physiological relevance in the context of fasting and caloric restriction is crucial. Such insights could aid in moving away from associations of gut bacterial signatures with metabolic diseases consistently reported in observational studies to potentially establishing causality. Therefore, this review aims to summarise what is currently known or still controversial about the interplay between fasting and caloric restriction, the gut microbiome and intestinal tissue physiology.

Bifidobacterium as a Potential Biomarker of Sarcopenia in Elderly Women

Gut microbial dysbiosis influences the development of sarcopenia. This case-control study explored the gut microbiota composition in elderly Chinese women with sarcopenia. The information from 50 cases and 50 controls was collected. Grip strength, body weight, body mass index, skeletal muscle mass, energy intake, and total and high-quality protein intake were lower in cases than in controls (p < 0.05). Gut microbiota metagenomic sequencing showed that phylum Bacteroides was significantly reduced in the case group, whereas genus Prevotella was more abundant (p < 0.05). Linear discriminant analysis (LDA) effect size showed that 9 and 13 distinct microbial taxa were enriched in the case and control groups, respectively (LDA > 2, p < 0.05), among which Prevotella copri and Bifidobacterium longum were significantly different (LDA > 4, p < 0.05). The AUC of Bifidobacterium longum was 0.674 (95% CI: 0.539-0.756). Elderly women with sarcopenia exhibited significantly different gut microbiota compositions than healthy controls.

Impact of caloric restriction on the gut microbiota

Caloric restriction (CR) and related time-restricted diets have been popularized as means of preventing metabolic disease while improving general well-being. However, evidence as to their long-term efficacy, adverse effects, and mechanisms of activity remains incompletely understood. The gut microbiota is modulated by such dietary approaches, yet causal evidence to its possible downstream impacts on host metabolism remains elusive. Herein, we discuss the positive and adverse influences of restrictive dietary interventions on gut microbiota composition and function, and their collective impacts on host health and disease risk. We highlight known mechanisms of microbiota influences on the host, such as modulation of bioactive metabolites, while discussing challenges in achieving mechanistic dietary-microbiota insights, including interindividual variability in dietary responses as well as other methodological and conceptual challenges. In all, causally understanding the impact of CR approaches on the gut microbiota may enable to better decode their overall influences on human physiology and disease.

Fasting and refeeding triggers specific changes in bile acid profiles and gut microbiota

BACKGROUND

Bile acids (BAs) are closely related to nutrient supply and modified by gut microbiota. Gut microbiota perturbations shape BA composition, which further affects host metabolism.

METHODS

We investigated BA profiles in plasma, feces, and liver of mice fed ad libitum, fasted for 24 h, fasted for 24 h and then refed for 24 h using ultraperformance liquid chromatography coupled to tandem mass spectrometry. Gut microbiota was measured by 16S rRNA gene sequencing. Expressions of BA biosynthesis-related genes in the liver and BA reabsorption-related genes in the ileum were analyzed.

FINDINGS

Compared with the controls, unconjugated primary BAs (PBAs) and unconjugated secondary BAs (SBAs) in plasma were decreased whereas conjugated SBAs in plasma, unconjugated PBAs, unconjugated SBAs and conjugated SBAs in feces, and unconjugated SBAs in liver were increased in the fasting mice. The expression of BA biosynthesis-related genes in the liver and BA reabsorption-related genes in the ileum were decreased in the fasting mice compared with the controls. Compared with the controls, Akkermansia, Parabacteroides, Muribaculum, Eubacterium_coprostanoligenes and Muribaculaceae were increased in the fasting mice whereas Lactobacillus and Bifidobacterium were decreased. All these changes in BAs and gut microbiota were recovered under refeeding. Akkermansia was negatively correlated with plasma levels of unconjugated PBAs, unconjugated SBAs and glucose, whereas it was positively correlated with plasma conjugated SBAs, fecal unconjugated PBAs, and fecal unconjugated SBAs.

CONCLUSIONS

We characterized the BA profiles, gut microbiota, and gene expression responsible for BA biosynthesis and intestinal reabsorption to explore their rapid changes in response to food availability. Our study highlighted the rapid effect of nutrient supply on BAs and gut microbiota.