The gut microbiome communicates with your body through a complex language of chemical signals known as microbiome byproducts. These metabolites, produced as microbes break down food and other substances, influence everything from digestion and immunity to mood and long-term health risk. This article explores how these hidden signals arise, what they can tell you about your gut's functional state, and why understanding them can move you from guessing about symptoms to gaining personalized insight. You will learn about the key categories of byproducts, foods that support their production, how to improve your microbiome through diet and lifestyle, and how modern testing can help decode your unique microbial activity.

Introduction: Microbiome Byproducts as the Gut's Hidden Signals

Defining Microbiome Byproducts and Why They Matter for Everyday Health

Microbiome byproducts, or metabolites, are the molecules generated when the trillions of bacteria, fungi, and other microbes in your intestinal tract metabolize dietary components, host secretions, and each other's waste. Unlike simply knowing which microbes are present, understanding these byproducts reveals the actual biochemical activity occurring in your gut. This matters for everyday health because these compounds are not waste; they are active signaling molecules that enter your bloodstream and interact with your cells, directly influencing physiological processes.

How These Metabolic Signals Connect to Digestion, Immunity, and Overall Well-being

The connection is systemic. For instance, certain byproducts help regulate intestinal motility and nutrient absorption, while others modulate the immune system's inflammatory response. Signals from the gut can even cross the blood-brain barrier, influencing neurotransmitter pathways related to mood and stress. Therefore, the profile of microbiome byproducts serves as a real-time report on how your gut ecosystem is functioning and interacting with your entire body.

What You'll Learn About Moving from Information to Actionable Awareness

This guide will help you translate the science of microbial metabolites into practical understanding. You'll learn how byproducts are formed, what shifts in their levels might indicate, and why there is no one-size-fits-all interpretation. We'll also discuss how tools like comprehensive microbiome analysis can provide a snapshot of these signals, offering a basis for personalized dietary and lifestyle strategies rather than universal prescriptions.

Core Explanation of the Topic

From Microbes to Metabolites: How Microbiome Byproducts Arise in the Gut

The process begins with what you eat. Dietary fibers, proteins, fats, and other compounds that escape human digestion travel to the colon, where they become fuel for resident microbes. Through complex enzymatic pathways, these microbes ferment and transform these substrates. For example, fiber fermentation by certain bacteria yields short-chain fatty acids (SCFAs), while protein metabolism can produce various indoles and phenols. This metabolic activity is dynamic, changing with every meal, stress event, or medication.

Key Categories of Microbiome Byproducts

Microbial metabolites fall into several functionally important groups:

• Short-Chain Fatty Acids (SCFAs): Butyrate, acetate, and propionate. Primarily from fiber fermentation, they are crucial for colon cell energy, anti-inflammatory signaling, and regulating appetite.
• Bile Acid Derivatives: Microbes modify host-produced bile acids, influencing fat digestion, cholesterol metabolism, and hepatic signaling.
• Tryptophan Metabolites: Indole and serotonin precursors. Derived from the amino acid tryptophan, these can impact gut barrier function and communication with the nervous system.
• Gases: Hydrogen, methane, and hydrogen sulfide, which can affect gut motility and sensation, often linked to symptoms like bloating.
• Vitamins: Certain gut microbes synthesize B vitamins and vitamin K, contributing to host nutritional status.
• Other Bioactive Molecules: Trimethylamine N-oxide (TMAO), linked to cardiovascular health, and various neuroactive compounds.

Reading the Signals: What Different Byproducts Indicate About Gut Function and Microbial Activity

Elevated or reduced levels of specific byproducts offer clues. High butyrate production often suggests robust fiber fermentation and a healthy colon environment, while elevated sulfide gases might indicate shifts in microbial groups that can irritate the gut lining. A profile with diverse SCFAs generally reflects a diverse, fiber-loving microbiome, whereas a dominance of protein fermentation products might suggest low dietary fiber intake or microbial imbalance. It's a language of biochemical patterns, not single biomarkers.

Why This Topic Matters for Gut Health

Direct Links to Digestion, Nutrient Absorption, and Barrier Integrity

SCFAs like butyrate are the primary energy source for colonocytes, the cells lining your colon, helping maintain a tight intestinal barrier. This barrier prevents unwanted substances from leaking into the bloodstream, a concept often called "leaky gut." Bile acid metabolites directly assist in fat absorption. Thus, the byproduct profile is a functional readout of digestive efficiency and gut structural health.

Influence on Immunity and Inflammation Via Metabolite Signaling

Many microbiome byproducts act as immune modulators. Butyrate, for example, promotes the activity of regulatory T-cells, which help dampen excessive inflammation. Conversely, some byproducts from dysbiotic metabolism can trigger pro-inflammatory pathways. The gut is the largest immune organ, and metabolites are key signals that educate immune cells, shaping systemic inflammatory tone.

Brain-Gut Axis and Mental Well-being: How Byproducts Can Relate to Mood, Sleep, and Energy

The gut-brain axis is a bidirectional communication network. Microbial metabolites like SCFAs and tryptophan derivatives can influence the production of serotonin and other neurotransmitters. They also affect the integrity of the blood-brain barrier and neuroinflammation. While not direct "cures" for mood disorders, these signals are a piece of the puzzle in understanding how gut health can contribute to feelings of well-being, sleep quality, and mental energy.

Related Symptoms, Signals, or Health Implications

Digestive Symptoms Tied to Byproduct Shifts: Bloating, Gas, Irregular Bowel Patterns, Discomfort

Changes in gas-producing metabolites (hydrogen, methane) are frequently associated with bloating and altered bowel habits. Reduced SCFA output may correlate with constipation or inflammation-driven diarrhea. Discomfort after eating can sometimes be traced to rapid shifts in microbial fermentation and byproduct production in response to specific foods.

Systemic Signals That May Accompany Gut-Derived Metabolites: Fatigue, Skin Health, Inflammatory Flares

When metabolite signaling promotes systemic inflammation, it may manifest as unexplained fatigue, skin conditions like eczema or acne, or joint discomfort. These are non-specific signals, meaning they have many potential causes, but a gut-derived component is increasingly recognized in holistic health models.

Long-Term Health Implications: Metabolic Signals, Autoimmune Risk, and Chronic Inflammation

Persistent imbalances in byproduct profiles are areas of scientific interest for long-term health. For instance, consistently low butyrate and elevated TMAO or certain bile acids have been associated in research with increased risks for metabolic conditions, cardiovascular issues, and autoimmune dysregulation. This underscores the importance of a balanced gut microbiome over the lifespan.

Individual Variability and Uncertainty

Inter-Individual Differences in Microbiome Composition and Metabolic Output

No two microbiomes are identical. Genetics, birth delivery method, lifelong diet, and environmental exposures create a unique microbial ecosystem in each person. Consequently, two people eating the same diet can produce vastly different quantities and types of microbiome byproducts. This variability makes population-level recommendations challenging and highlights the need for personalized insight.

Temporal Variability: Day-to-Day, Dietary, and Medication-Driven Changes

Your byproduct profile is not static. It fluctuates with daily food intake, stress levels, sleep, exercise, and medications like antibiotics or proton pump inhibitors. A single day of high-protein, low-fiber eating will shift the metabolic output temporarily. This dynamism is normal but means any snapshot from testing reflects a moment in time.

Interpreting Signals with Uncertainty: Probabilities, Not Certainties, and the Role of Context

It is crucial to frame byproduct levels as indicators of probability, not diagnosis. For example, low butyrate suggests a possible need for more dietary fiber or specific probiotics, but it does not diagnose a disease. Interpretation always requires context—symptom history, diet, lifestyle, and often professional guidance—to be meaningful.

Why Symptoms Alone Do Not Reveal the Root Cause

Symptom Overlap Across Gut Pathways and Conditions

Bloating, fatigue, or irregular bowels can result from dozens of different underlying issues—small intestinal bacterial overgrowth (SIBO), food intolerances, intestinal permeability, or motility disorders. The same symptom can arise from completely different imbalances in microbial byproduct production, making cause-and-effect difficult to deduce from symptoms alone.

Byproducts Reflect Ongoing Microbial Activity, Not a Single Root Cause

A byproduct profile shows the current metabolic outcome of your microbiome's activity. This outcome is the result of multiple interacting factors: microbial composition, diet, host physiology, and more. It is a readout of the system's state, not a pinpointed "root cause," which is often a network of contributors rather than a single entity.

The Pitfall of Inferring Diagnosis from Symptoms Without Seeing the Broader Metabolic Picture

Relying solely on symptoms can lead to guessing and trial-and-error approaches that may not address core imbalances. For instance, treating bloating with general probiotics might help or worsen the issue, depending on whether the underlying cause involves methane-producing archaea or hydrogen sulfide pathways. Deeper metabolic insight can reduce this guesswork.

The Role of the Gut Microbiome in This Topic

Microbiome Function (Metabolic Activity) Vs. Composition (Which Microbes Are Present)

This is a key distinction. Compositional tests identify which microbial species are present. Functional insight, often derived from byproduct analysis or genetic pathway prediction, reveals what those microbes are doing. Two people can have similar microbial lists but vastly different functional outputs based on diet and other factors. Activity, not just presence, dictates health impact.

Microbial Pathways That Generate Key Byproducts and How They Interconnect

The gut microbiome operates as a metabolic network. The production of one byproduct often affects another. For example, microbes that produce butyrate often rely on acetate produced by other bacteria. Pathways for bile acid metabolism interact with those for inflammatory signaling. Understanding these interconnections prevents oversimplifying any single metabolite's role.

Host Factors Shaping Byproduct Profiles: Diet, Medications, Genetics, and Lifestyle

The host is an active participant. Your diet provides the substrate; your genetics influence enzyme activity and receptor sensitivity to metabolites; medications can wipe out or encourage specific microbial pathways; and lifestyle factors like stress and sleep alter gut motility and pH, changing the microbial environment. The byproduct profile is a host-microbe collaborative effort.

How Microbiome Imbalances May Contribute

Dysbiosis and Altered Metabolite Output: Which Byproducts Rise or Fall

Dysbiosis, a state of microbial imbalance, often shifts metabolic output. Common patterns include a decrease in beneficial SCFAs like butyrate and an increase in potentially detrimental products like ammonia, certain phenols, or excessive gases. These shifts can alter the gut environment, sometimes perpetuating the dysbiotic state.

Common Imbalance Patterns

Patterns observed in research and clinical practice include:

• Reduced Butyrate Producers: Often linked to low dietary fiber, antibiotic use, or inflammation, associated with compromised gut barrier function.
• Shifts in Bile Acid Metabolism: An overgrowth of microbes that deconjugate bile acids too early can lead to bile acid diarrhea and altered fat metabolism.
• Protein Fermentation Dominance: When fiber is scarce, microbes may switch to fermenting proteins, producing metabolites that can be inflammatory or neuroactive at high levels.

Consequences for Gut Barrier, Inflammation, and Systemic Signaling

These altered patterns can weaken the intestinal barrier, allowing byproducts and other molecules to enter circulation in an unregulated way. This can trigger local and systemic immune responses, contributing to chronic low-grade inflammation, which is a suspected contributor to various long-term health conditions.

Foods and Dietary Patterns That Promote Beneficial Byproducts

Top Microbiome Foods: What to Eat Every Day for a Healthier Gut

Your diet is the most direct lever you have on microbiome byproduct production. To support the microbes that generate beneficial metabolites like butyrate, focus on a diverse range of plant-based fibers and fermented foods. Here are ten food groups to include regularly:

1. Legumes (lentils, chickpeas, beans) – rich in resistant starch and fiber that fuel SCFA production.
2. Whole grains (oats, barley, quinoa) – provide beta-glucan and other fermentable fibers.
3. Berries and apples – contain pectin and polyphenols that support microbial diversity.
4. Leafy greens and cruciferous vegetables – supply fiber and sulfur-containing compounds that can influence microbial metabolism.
5. Onions, garlic, and leeks – rich in inulin, a prebiotic fiber that feeds beneficial bacteria.
6. Bananas (especially slightly green) – a source of resistant starch.
7. Nuts and seeds (flax, chia, walnuts) – provide fiber and healthy fats that modulate bile acid metabolism.
8. Fermented foods (yogurt, kefir, sauerkraut, kimchi) – introduce live microbes that can contribute to metabolic activity.
9. Polyphenol-rich foods (dark chocolate, green tea, red grapes) – support microbial diversity and anti-inflammatory metabolites.
10. Bone broth (optional) – may provide amino acids and glycine that support gut lining integrity.

How to Fix Your Microbiome Through Diet and Lifestyle

Improving your microbiome isn't about a single magic food; it's about consistent patterns. Here are evidence-informed strategies to support a healthy byproduct profile:

• Eat a wide variety of plant foods (aim for 30+ different plant types per week) to increase microbial diversity.
• Include resistant starch from cooled potatoes, rice, or oats to feed butyrate-producers.
• Gradually increase fiber intake to avoid bloating while your microbes adapt.
• Limit ultra-processed foods and artificial sweeteners, which may negatively alter microbial populations.
• Manage stress through mindfulness, deep breathing, or gentle exercise, as stress hormones can shift gut motility and microbial activity.
• Prioritize sleep; circadian disruption can affect the microbiome's daily rhythms.
• Avoid unnecessary antibiotics and discuss any medication use with your doctor.

How Gut Microbiome Testing Provides Insight

What Microbiome Tests Measure: Composition, Functional Potential, and Metabolite Byproducts

Advanced testing can look at different layers. Sequencing (16S or shotgun metagenomics) infers which microbes are present and their genetic potential for functions. Direct metabolomic analysis of stool or blood measures the actual byproducts being produced. Some tests, like breath tests, measure specific gases (hydrogen, methane) indicative of microbial fermentation patterns in the small intestine.

Test Modalities to Consider

Different tests offer different insights:

• Sequencing-Based: Provides a detailed census of microbial species and predicted functions.
• Metabolomics: Directly measures a wide array of metabolites in a sample, giving a functional snapshot.
• Breath Tests: Useful for identifying specific patterns of gas production linked to conditions like SIBO.

Limitations and Interpretation: Snapshot Timing, Lab Variability, and the Need for Clinical Context

All tests have limitations. A stool sample is a single snapshot of a dynamic system. Different labs may use different methodologies. Importantly, results are not a standalone diagnosis; they are pieces of information that gain meaning when integrated with a person's clinical history, symptoms, and diet by a knowledgeable practitioner.

What a Microbiome Test Can Reveal in This Context

Specific Byproducts to Monitor and Their Health Implications

A comprehensive test might report levels of:

• SCFAs (Butyrate, Acetate, Propionate): Indicators of fiber fermentation and gut lining health.
• Bile Acids (Primary vs. Secondary): Insights into fat digestion and microbial modification activity.
• TMAO: A metabolite linked to dietary choline and carnitine metabolism, associated with cardiovascular health.
• Indoles and Phenols: Derived from protein and amino acid metabolism, can have mixed effects on barrier and inflammation.

How Results Can Align with Symptoms and Dietary Adjustments

For example, someone reporting bloating and fatigue might see test results showing low butyrate and elevated hydrogen sulfide markers. This could align with a diet low in diverse fibers and high in sulfur-containing foods, providing a targeted starting point for dietary modification rather than indiscriminate elimination.

Personalizing Strategies Based on Test Findings

Findings can inform personalized plans. Low butyrate might lead to introducing specific prebiotic fibers and potentially butyrate-producing probiotics. Altered bile acids could suggest dietary fat adjustments or specific binders. The goal is to use the data to make informed, incremental changes, often monitored over time with tools like a longitudinal gut health program to track progress.

Who Should Consider Testing

When Standard Workups Are Inconclusive or Symptoms Persist

Individuals who have undergone standard medical evaluations (e.g., for IBS, fatigue) without clear answers might find value in a deeper look at gut microbial function to identify contributing factors that conventional tests don't capture.

Recurrent Gut Symptoms with Systemic Signals

Those experiencing persistent digestive issues like bloating, irregularity, or discomfort alongside systemic concerns like unexplained fatigue, mood fluctuations, or skin problems may benefit, as these patterns often suggest gut-derived metabolic influences.

Post-Antibiotic Recovery, Food Intolerances, or Suspected Dysbiosis

After a course of antibiotics, which can significantly alter the microbiome, testing can provide a baseline. Similarly, for individuals with multiple food intolerances, understanding the microbial metabolic landscape can help tailor a reintroduction strategy.

Practical Considerations: Cost, Access, and the Value of Clinician Guidance

Testing involves cost and requires interpretation. The greatest value is realized when results are reviewed with a healthcare provider, nutritionist, or qualified practitioner who can translate the data into a safe, effective action plan. For practitioners themselves, understanding the available B2B platforms for microbiome analysis can be part of integrating this tool into practice.

Decision-Support Section

A Practical Decision Flow: Symptom Pattern, Duration, and Readiness for Testing

Consider testing if: You have chronic (>3 months) gut-related symptoms; symptoms are affecting your quality of life; you have already tried basic dietary adjustments (like a high-fiber diet) with limited success; and you are prepared to use the information as part of a longer-term learning process, not a quick fix.

When to Test Vs. When to Monitor with Dietary and Lifestyle Adjustments

For mild or new symptoms, a first step is often a period of mindful dietary change (e.g., increasing fiber diversity, reducing processed foods) and symptom journaling. If patterns persist or are severe, testing can offer clarity. Testing is a tool for when the guessing game becomes counterproductive.

Choosing a Reputable Test

Look for tests from reputable companies that use validated methods, provide clear reports on both composition and function (like metabolites), offer transparent information on their laboratory protocols, and emphasize the need for professional interpretation. Consider turnaround time and data privacy policies.

How to Prepare for Testing and How to Act on Results

Follow the test kit instructions carefully, which often involve avoiding probiotics, antibiotics, or certain supplements for a period before sampling. Once results are in, the most important step is to review them with a knowledgeable professional who can help you create a personalized, phased plan for dietary, supplemental, and lifestyle changes based on your unique profile.

Clear Concluding Section

Recap: Microbiome Byproducts as Personalized Health Signals Guiding Insight, Not Certainty

The metabolites produced by your gut microbiome are powerful, personalized signals that reflect the functional state of your inner ecosystem. They connect your diet and lifestyle to your digestive health, immune function, and even mental well-being. Understanding them provides insight, not definitive answers, guiding you toward more informed health decisions.

Embracing Uncertainty: Using Byproducts to Inform Thoughtful, Incremental Steps

Given the inherent variability and complexity of the microbiome, the goal is not to achieve a "perfect" byproduct profile but to use trends and patterns to make thoughtful, incremental adjustments. This is a process of learning and adapting, not a one-time correction.

Practical Next Steps

Begin by journaling your symptoms, diet, and energy levels to identify patterns. Experiment with evidence-based dietary tweaks, such as increasing a variety of plant-based fibers. If you reach a plateau or curiosity grows, discuss the option of microbiome testing with a healthcare professional to gain a deeper, personalized snapshot of your gut's metabolic activity.

Final Thought

Your gut microbiome is a dynamic, individual ecosystem that co-evolves with you. Investing time in understanding its hidden language of byproducts is an investment in a nuanced, long-term view of your health, empowering you to become an active participant in your own well-being.

Key Takeaways

• Microbiome byproducts are active metabolites that serve as communication signals between your gut and the rest of your body.
• Key categories include short-chain fatty acids, bile acid derivatives, tryptophan metabolites, and gases, each with distinct health implications.
• These byproducts directly influence digestion, gut barrier integrity, immune inflammation, and brain-gut axis communication.
• Symptoms like bloating or fatigue are non-specific and rarely point to a single root cause in the complex gut ecosystem.
• There is immense individual and temporal variability in byproduct production, making personalized insight valuable.
• Microbiome function (what microbes do) is as important as composition (which microbes are there).
• Dysbiosis can alter byproduct profiles, potentially contributing to gut barrier issues and systemic inflammation.
• A diet rich in diverse fibers and fermented foods supports beneficial byproduct production, while reducing ultra-processed foods may help.
• Advanced gut microbiome testing can provide a snapshot of these byproducts, offering data beyond symptoms alone.
• Testing is most useful for persistent, unexplained symptoms and should be interpreted with professional guidance.
• The goal is to use byproduct insight to inform personalized, incremental dietary and lifestyle strategies for long-term gut health.

Frequently Asked Questions

Q1: What exactly are microbiome byproducts? A1: Microbiome byproducts, or metabolites, are chemical compounds produced when the microbes in your gut break down dietary components like fiber, protein, and fats. They include substances like short-chain fatty acids, gases, and vitamins that actively influence your health.

Q2: What are 3-4 factors that affect your microbiome? A2: Several key factors shape your microbiome: diet (especially fiber intake), medications such as antibiotics, stress levels, and sleep quality. These influence which microbes thrive and what byproducts they produce.

Q3: How do short-chain fatty acids (SCFAs) benefit health? A3: SCFAs, such as butyrate, serve as the main energy source for colon cells, helping maintain a strong gut barrier. They also have anti-inflammatory effects and help regulate metabolism and appetite through signaling pathways.

Q4: Can my mood really be affected by my gut microbiome? A4: Indirectly, yes. Certain microbiome byproducts, like tryptophan metabolites and SCFAs, can influence the production and function of neurotransmitters like serotonin via the gut-brain axis, potentially impacting mood, stress response, and sleep patterns.

Q5: What are the top 10 microbiome foods? A5: Top microbiome foods include legumes, whole grains, berries, leafy greens, onions, bananas, nuts and seeds, fermented foods like yogurt and kefir, polyphenol-rich items like green tea and dark chocolate, and optionally bone broth (see the food list above for details).

Q6: Why do I experience bloating even when I eat healthy foods? A6: Bloating can result from the fermentation of certain fibers or sugars by your gut microbes, producing gases like hydrogen or methane. This depends on your unique microbial community and its metabolic pathways, which can be overly active or imbalanced, even with healthy foods.

Q7: What does a gut microbiome want you to eat every day? A7: Your gut microbiome thrives on a variety of plant-based fibers, resistant starches, and fermented foods. Daily habits like eating a diverse range of vegetables, fruits, whole grains, legumes, and adding a serving of fermented food can support beneficial byproduct production.

Q8: How do I fix the microbiome in my gut? A8: There is no one-size-fits-all fix, but foundational steps include eating more fiber-rich plants, reducing ultra-processed foods, managing stress, getting adequate sleep, staying physically active, and avoiding unnecessary antibiotics. A microbiome test can provide personalized insights if symptoms persist.

Q9: What is dysbiosis, and how does it change byproduct production? A9: Dysbiosis refers to an imbalance in the gut microbial community. It often leads to reduced production of beneficial byproducts like butyrate and increased production of potentially harmful metabolites from protein fermentation or altered bile acid metabolism, which can irritate the gut lining.

Q10: How is a microbiome test different from a standard stool test? A10: A standard stool test typically looks for pathogens, blood, or inflammation markers. A comprehensive microbiome test uses genetic sequencing or metabolomics to identify the types of microbes present and, importantly, measure or infer the levels of various functional byproducts they are producing.

Q11: If I take a microbiome test, will it tell me exactly what to eat? A11: Not exactly. The test provides data on your current microbial metabolic output. This information can highlight patterns—like low fiber fermentation—that suggest dietary adjustments. However, translating this into a specific meal plan requires professional interpretation and personal experimentation.

Q12: How often should I test my gut microbiome? A12: For most individuals, testing is not a frequent need. It can be useful as an initial baseline, and then perhaps after 3-6 months of significant dietary or lifestyle intervention to observe changes. Longitudinal tracking is more about monitoring trends than constant checking.

Q13: Are microbiome tests covered by insurance? A13: Most direct-to-consumer advanced microbiome tests are not typically covered by health insurance, as they are often considered for wellness and insight rather than standard disease diagnosis. It's important to check with your insurance provider and the testing company.

Q14: Can I improve my microbiome byproducts without testing? A14: Absolutely. Foundational practices like eating a diverse, fiber-rich diet (lots of plants), managing stress, getting adequate sleep, and avoiding unnecessary antibiotics are evidence-based ways to support a healthy microbial balance and, by extension, a favorable byproduct profile.

Q15: What does a high level of TMAO in a test indicate? A15: Elevated trimethylamine N-oxide (TMAO) suggests that your gut microbes are metabolizing dietary choline or carnitine (found in red meat, eggs, fish) into TMA, which your liver then converts to TMAO. Research associates persistently high TMAO with increased cardiovascular risk, indicating a potential area for dietary modulation.

Q16: Is testing useful if I have no digestive symptoms? A16: It can be, but the value proposition changes. For asymptomatic individuals, testing might satisfy curiosity or serve as an advanced wellness baseline. However, without symptoms or specific health goals, the actionable insights may be less clear, and resources might be better spent on proven health-promoting behaviors.

Keywords

Microbiome byproducts, gut metabolites, short-chain fatty acids, butyrate, gut-brain axis, microbial fermentation, dysbiosis, gut health testing, metabolomics, personalized nutrition, intestinal barrier, immune modulation, SCFAs, bile acids, TMAO, gut microbiome function, microbial activity, individual variability.