\nGut microbiota; Short-chain fatty acids (SCFAs); Dietary fiber; Butyrate; Fermentation; Metabolic health; Inflammation; Gut barrier; Dysbiosis; Toxin metabolism; Gut\u2013liver axis; Energetic symbiosis
\n1) Human microbiota: definition and role
\nDefinition
\nThe human microbiota is the collection of microorganisms (bacteria, viruses, and fungi) that live on and within the human body, particularly in the gut, and contribute to critical metabolic and immune functions. (Nature)
\nMain functions
\nDigestion and fermentation of non-digestible fibers \u2192 production of short-chain fatty acids (SCFAs), such as butyrate. (MDPI)
\nModulation of energy and glucose metabolism. (Nature)
\nMaintenance of the immune barrier and protection against pathogens. (Nature)
\nInvolvement in the gut\u2013liver and gut\u2013brain axes. (Atti dell\u2019Accademia Lancisiana)<\/p>\n
2) Interactions between the microbiota and toxins
\n2A \u2013 Microbiota \u2192 toxins\/metabolites
\nThe microbiota:
\nFerments dietary fibers [1], producing beneficial metabolites (SCFAs). (MDPI)
\nMetabolizes xenobiotics (environmental toxins, drugs, additives), influencing their chemical form and toxicity. (MDPI)
\nContributes to the intestinal barrier, limiting the absorption of harmful substances. (Atti dell\u2019Accademia Lancisiana)
\nRecent research:
\n1. Fan & Pedersen (2020): link the gut microbiota to the metabolism of food-derived compounds and toxins in humans. (Nature)
\n2. Tu et al. (2020): review on the microbiome and environmental toxicity (concept of gut microbiome toxicity). (MDPI)<\/p>\n
2B \u2013 Toxins \u2192 microbiota
\nSome agents negatively impact the microbiota:
\nAntibiotics \u2192 intestinal dysbiosis
\nPesticides\/heavy metals \u2192 alteration of microbial diversity
\nAlcohol and ultra-processed foods \u2192 emerging negative effects
\nEvidence examples:
\nEnvironmental and dietary factors can alter microbial balance and increase inflammation. (ScienceDirect)<\/p>\n
2C \u2013 Effects of dysbiosis
\nDysbiosis (microbiota imbalance) may lead to:
\nIntestinal inflammation
\nIncreased intestinal permeability (leaky gut)
\nMetabolic disorders (obesity, insulin resistance)
\nRecent scientific evidence:
\nReviews linking microbiota composition to metabolism and human health. (Nature)<\/p>\n
3) Factors influencing the microbiota
\nFactor
\nEffect
\nHigh-fiber diet
\n\u2191 diversity and SCFA production (MDPI)
\nPolyphenols (fruit\/vegetables, tea, wine, olive oil)
\nPositive modulation of the microbial community
\nAntibiotics
\n\u2193 biodiversity, \u2191 dysbiosis
\nAlcohol
\nMay damage the mucosa and promote permeability
\nUltra-processed foods
\nAssociated with dysbiosis (mechanisms still under investigation)
\nKey research:
\n1. Charnock & Telle-Hansen (2020): effects of fiber on the microbiota and metabolic health. (MDPI)
\n2. PubMed reviews (2023\u20132024): fiber and microbiota modulation with clinical implications in metabolic diseases. (PubMed)<\/p>\n
4) Toxin elimination: integrated physiological pathways
\nLiver
\nPhase I: structural modification of toxins (oxidation)
\nPhase II: conjugation \u2192 increased solubility
\nElimination via bile \u2192 intestine
\nThe microbiota may modify these metabolites and influence their recirculation
\nKidneys
\nFilter the blood
\nEliminate water-soluble toxins through urine
\nIntestine + microbiota
\nExcretion of toxins via feces
\nPhysical and metabolic barrier against the absorption of harmful compounds
\nLungs and skin
\nElimination of CO\u2082 and volatile compounds
\nMinor role in the detoxification of more complex molecules<\/p>\n
5) Integrative key concepts
\nSCFAs and health
\nProducts of bacterial fiber fermentation (e.g., butyrate) not only provide substrates for intestinal cells but also modulate inflammation and systemic metabolism. (MDPI)
\nMicrobiota and the gut\u2013liver axis
\nMicrobial metabolites influence hepatic metabolism, with potential effects on toxin handling and lipid metabolism. (Nature)
\nDiet and metabolic diseases
\nMicrobiota changes associated with low fiber intake are linked to obesity and type 2 diabetes. (PubMed)<\/p>\n
Mini-summary
\n1. The gut microbiota is an ecosystem of microorganisms that supports digestion, immunity, and metabolism; its alteration (dysbiosis) is associated with metabolic diseases. (Nature)
\n2. Non-digestible dietary fibers are fermented by gut microbes into beneficial compounds (SCFAs). (MDPI)
\n3. Microbiota and toxins influence each other: the microbiota can degrade or transform xenobiotics, while substances such as antibiotics and pollutants can alter microbial composition. (MDPI)
\n4. The body eliminates toxins through the liver, kidneys, intestine (with microbiota involvement), lungs, and skin.<\/p>\n
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In-depth section \u201cA\u201d: Types of fermentation in the gut microbiota
\nGut bacteria mainly ferment non-digestible fibers and complex carbohydrates, producing short-chain fatty acids (SCFAs) that are beneficial to the host (and not only to the host [1]). However, when protein intake is high or fiber intake is insufficient, protein fermentation may increase, leading to the production of potentially harmful metabolites.
\nFiber fermentation (beneficial):
\nSubstrates: dietary fibers, resistant starches, complex carbohydrates
\nProducts: butyrate, acetate, propionate
\nEffects: nourishment of colonocytes, strengthening of the intestinal barrier, modulation of inflammation and systemic metabolism
\nProtein fermentation (physiological but potentially harmful if excessive):
\nSubstrates: undigested proteins reaching the colon
\nProducts: ammonia, biogenic amines, hydrogen sulfide, phenolic compounds
\nEffects: increased intestinal permeability, inflammation, cellular stress, and dysbiosis if predominant
\nFats
\nFats are not fermented like fibers and carbohydrates, but they strongly influence the microbiota through modulation of bile acids and inflammation. The type of fat consumed (unsaturated vs saturated) contributes to shaping microbial composition.
\nIn summary:
\nA healthy microbiota is characterized by predominantly saccharolytic (fiber-based) fermentation, whereas excessive protein fermentation reflects a dietary and microbial imbalance.<\/p>\n
In-depth section \u201cB\u201d: Bacterial fermentation, carbohydrates, and energy in the microbiota
\nIntestinal bacterial fermentation does not exclusively involve dietary fibers but generally includes non-digestible carbohydrates and other substrates that reach the colon. It is important to distinguish between carbohydrates that are digested and absorbed by the human body and those that instead become metabolic substrates for the microbiota.
\nDigestible carbohydrates (such as glucose, sucrose, and refined starches) are absorbed in the small intestine and provide energy directly to the host. In contrast, dietary fibers, resistant starches, and non-digestible complex carbohydrates reach the colon, where they are fermented by gut bacteria.
\nDuring fermentation, bacteria produce short-chain fatty acids (SCFAs)\u2014mainly butyrate, acetate, and propionate\u2014which serve dual energetic and metabolic functions.
\nButyrate is the primary energy source for colon epithelial cells (colonocytes), contributing to intestinal barrier maintenance and regulation of local inflammation. Acetate and propionate, on the other hand, are partly absorbed and utilized systemically, contributing to hepatic, lipid, and glucose metabolism.
\nIt is essential to emphasize that fermentation is not only beneficial to the host but also represents the central energy mechanism of the microbiota itself. Gut bacteria are not passive entities: they require energy to maintain their metabolism, produce ATP, grow, and replicate. Fermentable substrates [1] therefore provide energy directly to microorganisms, while the produced metabolites represent the metabolic interface between the microbiota and the human organism.
\nThis relationship can be defined as energetic symbiosis: the microbiota derives energy from dietary substrates unusable by humans, and in return produces metabolites that positively influence intestinal physiology, systemic metabolism, and immune regulation. Disruption of this system\u2014such as through a lack of fermentable fiber\u2014compromises both bacterial metabolism and host benefits.<\/p>\n
In-depth section \u201cC\u201d: ATP production in gut bacteria and energetic interaction with the host
\nGut bacteria predominantly live under anaerobic conditions and obtain energy through fermentative processes. During the fermentation of non-digestible carbohydrates and dietary fibers, intestinal microorganisms produce ATP for their own metabolism, which is necessary for cellular maintenance, growth, and replication.
\nBacterial fermentation is less efficient than aerobic respiration in terms of energy yield, but it represents an essential metabolic strategy in the intestinal environment. In addition to bacterial ATP, this process generates final metabolites, particularly short-chain fatty acids (SCFAs) such as butyrate, acetate, and propionate.
\nButyrate plays a central role in the microbiota\u2013host interaction: it is the primary energy source for colonocytes, where it is oxidized in mitochondria to produce ATP. This energetic support is fundamental for maintaining the intestinal barrier, regulating inflammation, and preserving epithelial stability.
\nAcetate and propionate can enter the systemic circulation and contribute to hepatic, lipid, and glucose metabolism. In this way, products of bacterial metabolism directly influence the overall energy balance of the human organism.
\nThis relationship represents a true energetic symbiosis:
\nthe microbiota obtains energy from dietary substrates unusable by humans
\nthe host benefits from the produced metabolites, which support metabolism, intestinal integrity, and immune homeostasis
\nA reduction in fermentable substrates, as occurs in low-fiber diets, compromises both bacterial metabolism and energy availability for the intestinal epithelium, promoting dysbiosis and metabolic dysfunction.
\nIn summary
\nGut bacteria produce ATP (adenosine triphosphate) for their own metabolism through fermentative processes and generate short-chain fatty acids (SCFAs) that act as energetic substrates for intestinal cells. In particular, butyrate is used by colonocytes to produce ATP, contributing to intestinal barrier maintenance and modulating inflammatory processes and systemic metabolism.<\/p>\n
Clarification of terms
\nModulating inflammatory processes means regulating the intensity and duration of inflammation, an essential defense mechanism that can become harmful if chronic.
\nModulating systemic metabolism means actively influencing and regulating the chemical processes that convert food into energy throughout the entire organism.<\/p>\n","protected":false},"excerpt":{"rendered":"
Abstract The human gut microbiota is a complex ecosystem of microorganisms that plays a central role in digestion, immune function, metabolic regulation, and the handling of dietary and environmental toxins. Through the fermentation of non-digestible carbohydrates and fibers, gut bacteria produce short-chain fatty acids (SCFAs) such as butyrate, acetate, and propionate, which act as key […]<\/p>\n","protected":false},"author":2,"featured_media":0,"comment_status":"closed","ping_status":"closed","sticky":false,"template":"","format":"standard","meta":{"footnotes":""},"categories":[73],"tags":[2067,2065,1979,2077,725,2071,1889,2075,1957,2069,2073],"class_list":["post-12643","post","type-post","status-publish","format-standard","hentry","category-article","tag-butyrate","tag-dietary-fiber","tag-dysbiosis","tag-energetic-symbiosis","tag-fermentation","tag-gut-barrier","tag-gut-microbiota","tag-gut-liver-axis","tag-inflammation","tag-metabolic-health","tag-toxin-metabolism"],"yoast_head":"\n