A Scoping Review of the Relationship between Intermittent Fasting and the Human Gut Microbiota: Current Knowledge and Future Directions

Time Restricted Eating: A Valuable Alternative to Calorie Restriction for Addressing Obesity?

PURPOSE OF REVIEW

In this review, we summarize the molecular effects of time-restricted eating (TRE) and its possible role in appetite regulation. We also discuss the potential clinical benefits of TRE in obesity.

RECENT FINDINGS

TRE is an emerging dietary approach consisting in limiting food intake to a specific window of time each day. The rationale behind this strategy is to restore the circadian misalignment, commonly seen in obesity. Preclinical studies have shown that restricting food intake only during the active phase of the day can positively influence several cellular functions including senescence, mitochondrial activity, inflammation, autophagy and nutrients' sensing pathways. Furthermore, TRE may play a role by modulating appetite and satiety hormones, though further research is needed to clarify its exact mechanisms. Clinical trials involving patients with obesity or type 2 diabetes suggest that TRE can be effective for weight loss, but its broader effects on improving other clinical outcomes, such as cardiovascular risk factors, remain less certain. The epidemic proportions of obesity cause urgency to find dietary, pharmacological and surgical interventions that can be effective in the medium and long term. According to its molecular effects, TRE can be an interesting alternative to caloric restriction in the treatment of obesity, but the considerable variability across clinical trials regarding population, intervention, and follow-up duration makes it difficult to reach definitive conclusions.

Intermittent fasting as a treatment for obesity in young people: a scoping review

Intermittent fasting focuses on the timing of eating rather than diet quality or energy intake, with evidence supporting its effects on weight loss and improvements in cardiometabolic outcomes in adults with obesity. However, there is limited evidence for its feasibility and efficacy in young people. To address this, a scoping review was conducted to examine intermittent fasting regimens in individuals aged 10 to 25 for the treatment of obesity focusing on methodology, intervention parameters, outcomes, adherence, feasibility, and efficacy. Due to the paucity of evidence in this age group, to adequately assess feasibility and adherence, all published studies of intermittent fasting in this age category, regardless of weight status and treatment intention, were included in the review. The review included 34 studies (28 interventional studies and 6 observational studies) with 893 participants aged 12 to 25. Interventions varied with 9 studies in cohorts with obesity utilizing intermittent fasting as an obesity treatment. Thirteen studies utilized 8-h time-restricted eating. Primary outcomes included cardiometabolic risk factors (7/28), anthropometric measurements (7/28), body composition (5/28), muscular performance (4/28), feasibility (1/28), and others (4/28). All 9 studies conducted in young people with obesity reported some degree of weight loss, although the comparator groups varied significantly. This review underscores the various utilizations of intermittent fasting in this age group and highlights its potential in treating obesity. However, the findings emphasize the need for rigorous studies with standardized frameworks for feasibility to ensure comparability and determine intermittent fasting's practicality in this age group depending on the treatment outcome of interest.

Effects of Long-Term Fasting on Gut Microbiota, Serum Metabolome, and Their Association in Male Adults

BACKGROUND

Long-term fasting demonstrates greater therapeutic potential and broader application prospects in extreme environments than intermittent fasting.

METHOD

This pilot study of 10-day complete fasting (CF), with a small sample size of 13 volunteers, aimed to investigate the time-series impacts on gut microbiome, serum metabolome, and their interrelationships with biochemical indices.

RESULTS

The results show CF significantly affected gut microbiota diversity, composition, and interspecies interactions, characterized by an expansion of the Proteobacteria phylum (about six-fold) and a decrease in Bacteroidetes (about 50%) and Firmicutes (about 34%) populations. Notably, certain bacteria taxa exhibited complex interactions and strong correlations with serum metabolites implicated in energy and amino acid metabolism, with a particular focus on fatty acylcarnitines and tryptophan derivatives. A key focus of our study was the effect of Ruthenibacterium lactatiformans, which was highly increased during CF and exhibited a strong correlation with fat metabolic indicators. This bacterium was found to mitigate high-fat diet-induced obesity, glucose intolerance, dyslipidemia, and intestinal barrier dysfunction in animal experiments. These effects suggest its potential as a probiotic candidate for the amelioration of dyslipidemia and for mediating the benefits of fasting on fat metabolism.

CONCLUSIONS

Our pilot study suggests that alterations in gut microbiota during CF contribute to the shift of energy metabolic substrate and the establishment of a novel homeostatic state during prolonged fasting.

Intermittent fasting induced cerebral ischemic tolerance altered gut microbiome and increased levels of short-chain fatty acids to a beneficial phenotype

Preconditioning-induced cerebral ischemic tolerance is known to be a beneficial adaptation to protect the brain in an unavoidable event of stroke. We currently demonstrate that a short bout (6 weeks) of intermittent fasting (IF; 15 h fast/day) induces similar ischemic tolerance to that of a longer bout (12 weeks) in adult C57BL/6 male mice subjected to transient middle cerebral artery occlusion (MCAO). In addition, the 6 weeks IF regimen induced ischemic tolerance irrespective of age (3 months or 24 months) and sex. Mice subjected to transient MCAO following IF showed improved motor function recovery (rotarod and beam walk tests) between days 1 and 14 of reperfusion and smaller infarcts (T2-MRI) on day 1 of reperfusion compared with age/sex matched ad libitum (AL) controls. Diet influences the gut microbiome composition and stroke is known to promote gut bacterial dysbiosis. We presently show that IF promotes a beneficial phenotype of gut microbiome following transient MCAO compared with AL cohort. Furthermore, post-stroke levels of short-chain fatty acids (SCFAs), which are known to be neuroprotective, are higher in the fecal samples of the IF cohort compared with the AL cohort. Thus, our studies indicate the efficacy of IF in protecting the brain after stroke, irrespective of age and sex, probably by altering gut microbiome and SCFA production.

Regulation of metabolism by circadian rhythms: Support from time-restricted eating, intestinal microbiota & omics analysis

Circadian oscillatory system plays a key role in coordinating the metabolism of most organisms. Perturbation of genetic effects and misalignment of circadian rhythms result in circadian dysfunction and signs of metabolic disorders. The eating-fasting cycle can act on the peripheral circadian clocks, bypassing the photoperiod. Therefore, time-restricted eating (TRE) can improve metabolic health by adjusting eating rhythms, a process achieved through reprogramming of circadian genomes and metabolic programs at different tissue levels or remodeling of the intestinal microbiota, with omics technology allowing visualization of the regulatory processes. Here, we review recent advances in circadian regulation of metabolism, focus on the potential application of TRE for rescuing circadian dysfunction and metabolic disorders with the contribution of intestinal microbiota in between, and summarize the significance of omics technology.

Ketogenic Interventions in Autosomal Dominant Polycystic Kidney Disease: A Comprehensive Review of Current Evidence

Autosomal Dominant Polycystic Kidney Disease (ADPKD) is a genetic disorder characterized by the development and enlargement of multiple kidney cysts, leading to progressive kidney function decline. To date, Tolvaptan, the only approved treatment for this condition, is able to slow down the loss of annual kidney function without stopping the progression of the disease. Furthermore, this therapy is approved only for patients with rapid disease progression and its compliance is problematic because of the drug's impact on quality of life. The recent literature suggests that cystic cells are subject to several metabolic dysregulations, particularly in the glucose pathway, and mitochondrial abnormalities, leading to decreased oxidative phosphorylation and impaired fatty acid oxidation. This finding paved the way for new lines of research targeting potential therapeutic interventions for ADPKD. In particular, this review highlights the latest studies on the use of ketosis, through ketogenic dietary interventions (daily calorie restriction, intermittent fasting, time-restricted feeding, ketogenic diets, and exogenous ketosis), as a potential strategy for patients with ADPKD, and the possible involvement of microbiota in the ketogenic interventions' effect.

Intermittent Fasting in Youth: A Scoping Review

Intermittent fasting (IF) focuses on the timing of eating rather than diet quality or energy intake, with evidence supporting its effects on weight loss and cardiometabolic outcomes in adults. However, there is limited evidence for its efficacy in adolescents and emerging adults. To address this, a scoping review examined IF regimens in individuals aged 10 to 25, focusing on methodology, intervention parameters, outcomes, adherence, feasibility, and efficacy. The review included 39 studies with 731 participants aged 15 to 25. Methodologies varied, with 18 studies on time-restricted eating and others requiring caloric restriction. Primary outcomes included cardiometabolic risk factors (11/29), body composition (9/29), anthropometric measurements (8/29), and feasibility (2/29). Most studies reported significant weight loss. This review underscores IF's potential in treating obesity in this age group but highlights the need for rigorous studies with standardized frameworks for feasibility to ensure comparability and determine IF's practicality in this age group.

Causal roles of gut microbiota in cholangiocarcinoma etiology suggested by genetic study

BACKGROUND

Cholangiocarcinoma (CCA) is a highly malignant biliary tract cancer with poor prognosis. Previous studies have implicated the gut microbiota in CCA, but evidence for causal mechanisms is lacking.

AIM

To investigate the causal relationship between gut microbiota and CCA risk.

METHODS

We performed a two-sample mendelian randomization study to evaluate potential causal associations between gut microbiota and CCA risk using genome-wide association study summary statistics for 196 gut microbial taxa and CCA. Genetic variants were used as instrumental variables. Multiple sensitivity analyses assessed result robustness.

RESULTS

Fifteen gut microbial taxa showed significant causal associations with CCA risk. Higher genetically predicted abundance of genus Eubacteriumnodatum group, genus Ruminococcustorques group, genus Coprococcus, genus Dorea, and phylum Actinobacteria were associated with reduced risk of gallbladder cancer and extrahepatic CCA. Increased intrahepatic CCA risk was associated with higher abundance of family Veillonellaceae, genus Alistipes, order Enterobacteriales, and phylum Firmicutes. Protective effects against CCA were suggested for genus Collinsella, genus Eisenbergiella, genus Anaerostipes, genus Paraprevotella, genus Parasutterella, and phylum Verrucomicrobia. Sensitivity analyses indicated these findings were reliable without pleiotropy.

CONCLUSION

This pioneering study provides novel evidence that specific gut microbiota may play causal roles in CCA risk. Further experimental validation of these candidate microbes is warranted to consolidate causality and mechanisms.

Targeting systemic inflammation in metabolic disorders. A therapeutic candidate for the prevention of cardiovascular diseases?

Cardiovascular disease (CVD) remains the leading cause of death and disability worldwide. While many factors can contribute to CVD, atherosclerosis is the cardinal underlying pathology, and its development is associated with several metabolic risk factors including dyslipidemia and obesity. Recent studies have definitively demonstrated a link between low-grade systemic inflammation and two relevant metabolic abnormalities: hypercholesterolemia and obesity. Interestingly, both metabolic disorders are also associated with endothelial dysfunction/activation, a proinflammatory and prothrombotic phenotype of the endothelium that involves leukocyte infiltration into the arterial wall, one of the earliest stages of atherogenesis. This article reviews the current literature on the intricate relationship between hypercholesterolemia and obesity and the associated systemic inflammation and endothelial dysfunction, and discusses the effectiveness of present, emerging and in-development pharmacological therapies used to treat these metabolic disorders with a focus on their effects on the associated systemic inflammatory state and cardiovascular risk.