The study, known as LEANER, enrolled 38 healthy adults who completed a five-day fasting protocol and were followed for twelve weeks afterward in a randomized, waitlist-controlled design. Fasting interventions have surged in popularity over the past decade, yet high-quality controlled data in healthy adults, with longer follow-up and multi-omics profiling, have remained scarce. This trial was designed to close that gap. Researchers tracked body mass index and body composition, sequenced gut microbiome composition, and measured both plasma and fecal metabolites before the fast, at its conclusion, and throughout the three-month follow-up period. Changes over time and between fasting and waitlist groups were evaluated with regression-based models and paired non-parametric tests, while permutation-based multivariate testing was applied to microbiome and metabolome data to detect coordinated shifts across hundreds of microbial species and metabolites simultaneously.

The acute results confirmed what smaller studies had hinted at: fasting rapidly lowered body mass index, and the reduction was driven predominantly by the loss of fat mass rather than lean tissue. Crucially, some of that improvement persisted at twelve weeks, even after participants returned to their ordinary eating habits. Alongside the changes on the scale, the fast produced marked remodeling of the gut microbiome and of metabolite profiles in both blood and stool. The researchers observed that post-fasting and longer-term changes in microbial diversity were associated with each participant’s baseline microbiome diversity, an observation with potentially significant implications. If the state of the gut ecosystem before fasting shapes how it responds and rebounds afterward, then the microbiome is not merely a passive bystander in the fasting response but a determining factor in its durability.

The heart of the study, however, lay in its predictive modeling. Rather than simply cataloguing what changed, the team asked whether pre-intervention data alone could forecast who would respond best. They built a data-driven machine learning model combining baseline microbiome features with clinical variables to predict individual body mass index response at twelve weeks, training and testing it with rigorous cross-validation inside the trial. The approach is technically demanding: with hundreds of candidate microbial species and dozens of clinical covariates measured in a modestly sized cohort, the risk of overfitting is substantial. Cross-validation, in which the model repeatedly trains on most participants and is tested on held-out individuals, provides a safeguard, ensuring that reported predictive performance reflects genuine signal rather than memorized noise.

Among the most prominent predictors identified were two specific gut bacteria: an unclassified species of Faecalibacterium, a genus widely associated with anti-inflammatory activity and the production of short-chain fatty acids, and Oscillibacter sp. 50_27. Clinical variables also carried weight, with baseline low-density lipoprotein cholesterol and systolic blood pressure emerging as key predictors alongside the microbial features. The inclusion of both domains is what distinguishes the model from earlier attempts at personalized nutrition forecasting. Microbial taxa capture the ecology of the gut ecosystem, while lipoprotein levels and blood pressure reflect systemic cardiometabolic status, and the model’s reliance on both suggests that sustained weight-loss response after fasting is a whole-body phenomenon rather than a purely intestinal one.

The most convincing evidence for the model came from its performance beyond the original trial. The team validated the model externally in three independent cohorts of people undergoing prolonged fasting protocols: individuals with metabolic syndrome, patients with multiple sclerosis who had been exposed to repeated fasting, and healthy volunteers fasting for six to twelve days. These cohorts differed in health status, fasting duration, and study context, yet the model retained its ability to stratify expected responses. External validation of this kind is rare in microbiome-prediction research, where many published models collapse when applied outside their discovery dataset. The authors note that their study was prospectively registered at ClinicalTrials.gov under identifier NCT04452916, and that the analysis pipeline and feature lists were made available, supporting reproducibility.

The mechanistic implications are already intriguing researchers. Faecalibacterium and Oscillibacter are both fermenters that produce metabolites capable of influencing host energy balance, inflammation, and even blood pressure regulation. The team supplemented their modeling with correlation analyses linking these species to fecal metabolites, hinting at concrete biochemical routes through which the gut ecosystem might modulate how the body stores and sheds fat. One plausible reading is that a microbiome already enriched in certain butyrate-producing organisms sets the metabolic stage for a more durable response to caloric deprivation, while a different starting community biases the body toward rebound weight gain. The new study does not prove causation, and the authors are appropriately cautious on this point, but it establishes a clear testable framework for intervention studies that manipulate the microbiome before fasting.

The clinical stakes are considerable. Obesity and metabolic syndrome affect hundreds of millions of people worldwide, and prolonged fasting has moved from fringe practice to mainstream interest, with medically supervised programs in Germany and elsewhere offering fasts lasting from five days to several weeks. Yet response is notoriously variable, and no simple biomarker currently tells a clinician whether a given patient will benefit. A validated predictive panel combining a microbiome profile with standard clinical labs such as LDL cholesterol and blood pressure could, in principle, allow physicians to identify likely responders before recommending an intensive intervention, and to direct those predicted to respond poorly toward alternative strategies. It would also help researchers design better trials, stratifying participants by predicted response and reducing the noise that has historically obscured modest but real effects in nutrition studies.

Limitations remain. The discovery cohort comprised 38 healthy adults, a sample small by machine learning standards even if the external validation cohorts bolster confidence in generalizability. The fasting protocol was short and the follow-up limited to twelve weeks, so predictions of response over one year or longer remain untested. Microbiome sequencing and metabolomics also vary across platforms and laboratories, meaning the specific model would need retraining or calibration before deployment in new settings. Still, the study represents one of the most rigorous demonstrations to date that routine pre-intervention biology can forecast the long-term outcome of a dietary intervention. As the authors conclude, baseline microbiome and clinical characteristics can help stratify expected longer-term responses, supporting the development of individualized, fasting-based interventions. In a field crowded with hype and one-size-fits-all promises, that measured claim, backed by cross-validation and replication across three independent populations, may prove to be the study’s most durable contribution.

Subject of Research: Machine learning prediction of sustained weight loss after prolonged fasting using baseline gut microbiome and clinical data

Article Title: Machine learning identifies microbiome and clinical predictors of sustained weight loss following prolonged fasting

Article References: Machine learning identifies microbiome and clinical predictors of sustained weight loss following prolonged fasting. (n.d.). https://doi.org/10.1186/s13073-026-01765-0

Image Credits: AI Generated

DOI: 10.1186/s13073-026-01765-0

Keywords: prolonged fasting, gut microbiome, machine learning, weight loss, metabolic health, Faecalibacterium, Oscillibacter, multi-omics, personalized nutrition, precision medicine, body mass index, Genome Medicine

Obesity currently affects more than one billion people worldwide and is classified by the World Health Organization as a chronic, multifactorial disease defined by the excessive accumulation of adipose tissue. Its consequences reach far beyond body weight, extending into type 2 diabetes, cardiovascular disease, non-alcoholic fatty liver disease and several cancers. The global economic burden is projected to reach trillions of US dollars annually by 2035. Yet existing treatments remain imperfect. Lifestyle interventions suffer from poor long-term adherence and frequent weight regain; pharmacological options such as GLP-1 receptor agonists and orlistat carry side effects ranging from gastrointestinal distress to cardiovascular risks, along with substantial costs; and bariatric surgery, while effective, is invasive and accessible to only a small fraction of those who need it. This treatment gap has driven growing scientific interest in food-derived bioactives as safer, more accessible complements or alternatives.

Rhizomes—the underground stems of plants such as turmeric (Curcuma longa), ginger (Zingiber officinale) and kencur (Kaempferia galanga)—are dense repositories of polyphenols, flavonoids and essential oils. However, many of their most celebrated compounds, including curcumin, suffer from notoriously poor water solubility, rapid systemic clearance and low oral bioavailability, which sharply constrain their therapeutic efficacy in conventional preparations. Fermentation offers a bioprocessing solution. When microorganisms such as lactic acid bacteria or filamentous fungi colonize the starch- and fibre-rich rhizome matrix, their enzymes cleave glycosidic and ester linkages, deconjugate polyphenols and generate structurally novel metabolites that simply do not exist in the raw plant. In one striking example documented in the review, fermentation of wild turmeric (Curcuma aromatica) with the fungus Rhizopus oligosporus produced l-carnitine de novo—a compound essential for transporting fatty acids into mitochondria for fat burning—reaching concentrations of up to 242 micrograms per gram, despite being absent from the unfermented substrate.

The metabolic by-products of this microbial transformation fall under the heading of postbiotics, a term defined by the International Scientific Association for Probiotics and Prebiotics as preparations of inanimate microorganisms and their components that confer a health benefit. Unlike probiotics, postbiotics do not require viable microorganisms, offering advantages in shelf stability, safety and standardization. Key postbiotic constituents generated during rhizome fermentation include short-chain fatty acids, bacteriocins, exopolysaccharides, bioactive peptides and biotransformed polyphenolic metabolites. The review’s authors are careful to note a nomenclature issue: because most included studies did not confirm microbial inactivation before administering their preparations, the team distinguishes throughout between “fermented rhizome products” as whole matrices and postbiotics in the strict sense, reserving the latter term for the specific bioactive metabolites hypothesized to mediate the observed effects.

To build this mechanistic framework, the researchers conducted the review under PRISMA guidelines, prospectively registering the protocol in PROSPERO. They searched four major databases—PubMed, Scopus, Web of Science and Embase—covering all records through April 2026, and screened 1307 initial records down to ten studies that met rigorous inclusion criteria. These comprised eight in vivo animal studies and two in vitro cell-culture studies spanning five rhizome species, with turmeric the most frequently investigated. Fermentation organisms were dominated by lactic acid bacteria, particularly Lactobacillus plantarum and L. paracasei, alongside filamentous fungi including Aspergillus oryzae, Eurotium cristatum and Rhizopus oligosporus. Animal models ranged from high-fat-diet-induced obesity in C57BL/6 mice and Sprague-Dawley rats to genetic obesity in ob/ob mice and spontaneous obesity in OLETF rats. Risk of bias was assessed using SYRCLE’s tool for animal studies and the ToxRTool for in vitro work, with both cell-culture studies achieving the highest reliability category.

Perhaps the most compelling evidence came from the six studies that directly compared fermented against unfermented preparations. In every single head-to-head comparison, the fermented product outperformed its unfermented counterpart on at least one assessed outcome. Fermented Rhizoma Atractylodis Macrocephalae more effectively reduced adipose tissue weight and improved serum triglycerides than the raw rhizome. Fermented turmeric suppressed weight gain and modulated gut microbiota more powerfully than unfermented turmeric—even though fermentation had actually reduced its curcuminoid content, a paradox suggesting that benefits may flow from biotransformed compounds, enhanced bioavailability or fermentation-derived metabolites rather than the parent phytochemicals alone. Fermented Panax notoginseng uniquely suppressed food intake and produced stronger weight reduction than the raw preparation, while fermented Polygonatum polysaccharides showed superior inhibition of adipogenesis in vitro.

The gut microbiota emerged as a central mediator of these effects. Across four in vivo studies that profiled host gut bacteria, fermented rhizome treatment consistently improved the ratio of Bacteroidetes to Firmicutes—a microbial signature repeatedly disrupted in obesity—and restored alpha diversity toward levels seen in normal-diet controls. Particularly striking was the enrichment of Akkermansia muciniphila, a mucus-degrading bacterium strongly associated with improved metabolic health and reduced gut permeability, which appeared in three independent studies using taxonomically distinct rhizome species. Fermented turmeric treatment also elevated faecal acetic, propionic and butyric acids—short-chain fatty acids that act through G-protein-coupled receptors to regulate lipid oxidation, insulin secretion and energy expenditure. Butyrate in particular was linked to the activation of thermogenic pathways in brown adipose tissue through upregulation of the metabolic enzymes ACSM3 and HADH, providing a direct microbiota-to-calorie-burning communication axis.

At the molecular level, the review identified at least six mechanistic axes of action. Suppression of adipogenesis—the process by which precursor cells mature into fat-storing adipocytes—was the most broadly shared, with multiple studies reporting downregulation of the master transcription factors PPAR-γ and C/EBPα and their downstream lipogenic enzymes. Conversely, lipolysis was enhanced through upregulation of HSL and ATGL and activation of PKA signalling. AMP-activated protein kinase, or AMPK, served as a central convergence node; in the most mechanistically complete study, fermented turmeric activated the AMPK–SIRT1–PGC-1α signalling triad, restoring mitochondrial oxidative capacity and energy expenditure while simultaneously suppressing endoplasmic reticulum stress and Nox4-mediated oxidative damage. Additional axes included improved insulin signalling via the PI3K/Akt pathway, attenuation of inflammatory cytokines including TNF-α, IL-6 and IL-1β, restoration of intestinal barrier integrity with reduced circulating endotoxin, and modulation of hypothalamic appetite regulation.

The metabolic results across the animal studies were substantive. All eight in vivo studies reported reductions in body weight gain or adipose tissue mass, and lipid profiles improved consistently, with reductions in serum and hepatic triglycerides in seven studies and HDL-cholesterol increases in four. One dose-response study documented that fermented turmeric extract at 200 and 500 milligrams per kilogram reduced weight gain by 12 and 22 percent respectively, while raising HDL-cholesterol by 53 to 67 percent. Glucose metabolism improved in the four studies assessing it, with reductions in fasting glucose, insulin and HOMA-IR, and thermogenic markers such as UCP-1 and adiponectin rose across several investigations.

The authors temper their enthusiasm with appropriate scientific caution. Using the OHAT framework, they rated the certainty of evidence as low or very low across all mechanistic axes, reflecting an entirely preclinical evidence base with predominantly unclear-to-high risk of bias in areas such as randomization and blinding. Substantial heterogeneity—five rhizome species, seven fermentation organisms, three product forms and multiple obesity models—prevented even a restricted quantitative meta-analysis. No human clinical data exist for these preparations. Nevertheless, the mechanistic coherence and cross-species consistency of the findings provide a preliminary foundation for the development of rhizome-based functional foods. The research team calls for randomized human intervention trials with standardized preparations, germ-free animal models to formally establish causal microbiota mechanisms, and bioactivity-guided fractionation to attribute specific effects to defined postbiotic compounds. If those trials succeed, the humble fermenting vat—humanity’s oldest food technology—may yet yield a new generation of evidence-based dietary tools against obesity.

The human gut microbiota, a complex ecosystem comprising trillions of microorganisms, has become increasingly recognized as a significant player in central nervous system function, mood regulation, and metabolic health. Alterations in this microbial landscape—dysbiosis—have been linked to numerous neuropsychiatric disorders including depression and bipolar affective disorder. The current research adds a nuanced layer to this understanding by focusing on acetate, a short-chain fatty acid (SCFA) produced naturally through bacterial fermentation of dietary fibers, known for its multiple biological roles including immune modulation, gut barrier integrity enhancement, and systemic metabolic influence.

Previous studies have underscored the compromised metabolic profile that frequently accompanies the use of psychotropic drugs, often leading to weight gain, insulin resistance, and lipid abnormalities. Such adversities not only complicate psychiatric management but also elevate cardiovascular risk. The innovative approach adopted in this study targets a dual path: harnessing the microbiome’s intrinsic metabolic mediation while concurrently aiming to rectify mood disturbances through systemic and neurochemical routes influenced by SCFAs.

This case-series systematically administered oral acetate supplements to a group of patients diagnosed with affective disorders and undergoing standard psychotropic regimens. The supplementation was designed to elevate systemic acetate levels, thereby exerting downstream effects on gut microbial composition and host metabolism. Intricate microbiome analyses, metabolic profiling, and psychiatric assessments were conducted longitudinally to delineate the trajectories induced by this intervention.

Encouragingly, the findings revealed substantive shifts in gut microbiota composition, characterized by an increase in beneficial bacterial taxa known to produce SCFAs and a reduction in potentially pathogenic microbes. This rebalancing was correlated with marked improvements in metabolic indices such as glycemic control and lipid profiles, which are critical for both physical health and the optimization of psychiatric treatment outcomes.

Furthermore, psychometric evaluations indicated a trend towards amelioration of affective symptoms. While the mechanistic underpinnings remain to be fully delineated, it is hypothesized that systemic acetate influences neuroinflammatory pathways and modulates neurochemical signaling, possibly through the gut-brain axis. This axis, a bidirectional communication network between the gastrointestinal tract and the central nervous system, involves neural, hormonal, and immunological signaling pathways, which are increasingly appreciated as therapeutic targets.

The study’s integrative approach offers compelling evidence supporting the microbiota-metabolism-psychiatry nexus. It highlights acetate not merely as a metabolic substrate but as a bioactive compound capable of mediating complex crosstalk between microbial metabolites and host physiology, ultimately influencing mood regulation and metabolic health in psychiatric patients.

Despite the promising nature of these preliminary results, the authors emphasize the necessity for expanded randomized controlled trials to validate efficacy, dosing paradigms, and long-term safety of acetate supplementation. Understanding patient-specific microbiome profiles and their dynamic response to such interventions may foster the advent of personalized medicine in psychiatric care.

Moreover, this exploration raises intriguing questions about the potential of dietary modifications—such as increased fiber intake to naturally boost SCFA production—as adjunctive treatments for affective disorders. It also sheds light on the broader implications of microbiome-targeted therapies in mitigating the metabolic side effects burdening patients on long-term psychotropic medication.

From a biochemical perspective, acetate functions as a substrate for acetyl-CoA synthesis, a pivotal molecule in energy metabolism and epigenetic regulation. This biochemical pathway may explain some of the observed systemic effects, linking the gut microbiome’s metabolic outputs to gene expression changes within the host’s neuronal and peripheral tissues.

The research also underscores the complexity of psychotropic drug impact on host physiology beyond neurotransmitter modulation, extending into metabolic and microbial ecosystems. Incorporating microbiome modulation strategies could revolutionize therapeutic frameworks, enhancing efficacy and minimizing adverse effects.

This scientific advance exemplifies the growing transcendence of siloed medical disciplines, where neuropsychiatry, microbiology, and metabolic medicine converge. It calls for multidisciplinary collaboration in both research and clinical practice to harness the potential of microbiota-based interventions in psychiatric populations.

In sum, the documented case-series serves as a vital proof-of-concept that oral acetate supplementation can beneficially alter gut microbiota and improve metabolic parameters in patients with affective disorders treated with psychotropics, with promising implications for mood symptom management. This novel therapeutic direction could signify a paradigm shift, inviting clinicians and researchers alike to reimagine mental health treatments through a microbiome-centered lens.

As this line of investigation unfolds, it promises to unlock unprecedented opportunities for non-invasive, adjunctive therapies that target the root of complex interactions between the mind and body. The science community, patients, and healthcare providers await with anticipation the outcomes of larger-scale studies that might confirm acetate’s role as a cornerstone in future psychiatric therapeutic strategies.

Subject of Research: Alteration of gut microbiota and metabolic improvement through oral acetate supplementation in patients with affective disorders on psychotropic medication.

Article Title: A case-series of oral acetate supplementation for gut microbiota alteration and metabolic improvement in patients with affective disorders on psychotropics.

Article References:
Al, K.F., Wammes, M., Warren, M. et al. A case-series of oral acetate supplementation for gut microbiota alteration and metabolic improvement in patients with affective disorders on psychotropics. Transl Psychiatry (2026). https://doi.org/10.1038/s41398-026-04046-x

Image Credits: AI Generated

DOI: https://doi.org/10.1038/s41398-026-04046-x

The study, led by Dr. Katsumi Iizuka of Fujita Health University and Dr. Hiroaki Masuyama of Symbiosis Solutions Inc., embarked upon an empirical investigation of gut microbiota compositional differences, analyzing a cohort of 80 women split evenly between underweight (BMI <17.5) and normal-weight (BMI between 18.5 and 25) categories. Utilizing standardized stool sampling techniques and comprehensive food frequency questionnaires, the research team evaluated both the microbial diversity within the gut and the dietary intake profiles of participants. Intriguingly, despite controlled dietary inputs reflecting no statistically significant differences, substantial disparities emerged in gut microbial diversity indices, highlighting the nuanced role of endogenous gut ecology in shaping host health.

Alpha and beta diversity metrics, reflecting within-sample and between-sample microbial richness and composition, respectively, revealed markedly diminished diversity in the underweight group. Reduced alpha diversity, often linked to compromised gut ecosystem resilience and impaired metabolic functionality, was coupled with an increased enrichment of specific bacterial taxa such as Bacteroides, Bifidobacterium, and Erysipelatoclostridium. These genera are associated with pro-inflammatory states and have been implicated in metabolic dysregulation in prior studies, suggesting a potentially pathogenic role of altered microbiota in the maintenance of low body weight.

Conversely, normal-weight participants exhibited greater abundance of beneficial microbes like Prevotella and Dorea, taxa correlated with anti-inflammatory properties and efficient carbohydrate metabolism. These findings underscore not only qualitative but also functional divergences in gut microbiota between the two cohorts, raising provocative questions regarding causal pathways linking microbial ecology, systemic inflammation, and body weight regulation. This empirical evidence challenges the traditional paradigms that regard dietary intake as the primary modifiable factor in weight management, positioning gut microbiota diversity as a crucial variable in metabolic homeostasis.

The implications of these findings are profound, particularly in the context of Japan’s rising trend of underweight young women—a trend persisting unmitigated over two decades despite public health interventions. Low body weight in this population is associated with a spectrum of deleterious outcomes, including menstrual irregularities, infertility, compromised immune responses, and persistent reductions in bone mineral density. The study’s revelation that gut microbial alterations are present even in the absence of divergent dietary behaviors suggests that therapeutic strategies should extend beyond caloric or macronutrient adjustments to incorporate interventions targeting the restoration and maintenance of microbial diversity.

Dr. Iizuka emphasized the potential for dietary fiber and fermented food intake to serve as modulators of gut microbiota composition, capable of mediating shifts towards healthier microbial communities conducive to weight stabilization. Fermented foods, rich in live microorganisms, and dietary fibers, which serve as prebiotic substrates, may collectively remodel the gut ecosystem, attenuating inflammatory taxa while promoting beneficial microbes. Such interventional strategies could herald a paradigm shift in clinical nutrition, particularly for underweight individuals whose gut microbial profiles predispose them to systemic inflammation and metabolic inefficiency.

Furthermore, the fusion of gut microbiota profiling with dietary survey data offers promising avenues for personalized nutritional medicine. Beyond caloric and macronutrient quantification, real-time assessments of postprandial microbial metabolism and gut mucosal interactions could inform dynamic, individualized dietary prescriptions. This approach aligns with the broader precision medicine movement, aiming to integrate microbiome analytics into routine clinical workflows to optimize health outcomes and chronic disease management.

The pathophysiological mechanisms underpinning the observed microbiota differences remain an active domain of inquiry. Hypotheses posit that reduced microbial diversity impairs short-chain fatty acid production, critical for intestinal barrier function and systemic metabolic regulation, thus fostering chronic low-grade inflammation and energy underutilization. Concurrently, the prevalence of inflammation-associated taxa in the underweight group may perpetuate mucosal immune activation, leading to nutrient malabsorption and metabolic inefficiencies exacerbating low body mass index conditions.

This study’s robust methodology—age-matched cohorts, stringent sample collection protocols, and comprehensive dietary analyses—strengthens the credibility of its conclusions. Moreover, by focusing on a homogeneous population within a defined geographic and cultural context, the research provides insights that are both regionally relevant and globally translatable, given the ubiquity of gut microbiota influences on metabolic health.

As Japan and other nations contend with shifting demographic and nutritional landscapes, integrating microbiota-based diagnostics and therapeutics could redefine approaches to managing undernutrition and associated metabolic disorders. The current findings propel the research community toward elucidating precise microbial signatures and functional pathways that underpin body weight regulation, thereby informing novel probiotic, prebiotic, and synbiotic interventions.

In synthesis, this landmark study delineates how gut microbiota diversity—not dietary pattern differences—is a significant discriminator between underweight and normal-weight young Japanese women. Recognition of this microbiota-body weight nexus invites a reevaluation of nutritional guidelines and underscores the exigency for a microbiome-conscious framework in clinical nutrition and public health strategies targeted at vulnerable populations.

Overall, the emerging narrative positions the gut microbiota as both a sentinel and mediator of nutritional status, demanding multidisciplinary efforts to unravel its complexities and translate microbiome science into impactful health solutions. As research progresses, harnessing microbial ecosystems may not only ameliorate underweight conditions but also advance broader metabolic and immunological wellbeing.

Subject of Research: People
Article Title: Gut Microbiota α- and β-Diversity, but Not Dietary Patterns, Differ Between Underweight and Normal-Weight Japanese Women Aged 20–39 Years
News Publication Date: 17-Oct-2025
Web References: https://doi.org/10.3390/nu17203265
References: DOI 10.3390/nu17203265
Image Credits: Dr. Katsumi Iizuka from Fujita Health University, Japan
Keywords: gut microbiota, underweight, Japanese women, gut microbial diversity, body weight, inflammation, dietary patterns, probiotics, prebiotics, metabolic health, clinical nutrition