What Are Prebiotics and Probiotics — And Do You Need Both?
Prebiotics. Probiotics. Synbiotics. Postbiotics. The gut health space has never had more terminology — and if you've ever stood in a health food store wondering what any of it actually means, you're in good company.
Gut health has become one of the most significant areas of nutritional science in the past decade, and for good reason. Research is increasingly linking the state of your gut microbiome to everything from digestion and immune function to mental health, energy levels, skin health and metabolic wellbeing.
But do you actually need to supplement with prebiotics and probiotics? What's the difference between them? And do you need both?
In this guide, we cut through the confusion with a clear, science-backed explanation of what prebiotics and probiotics are, what they each do, how they work together, and the best ways to get more of both — including some brilliant products from the Keto Direct gut health range.
What Is the Gut Microbiome?
Before we get into prebiotics and probiotics, it helps to understand what we're actually trying to support.
Your gut microbiome is the vast, complex community of microorganisms — bacteria, viruses, fungi and other microbes — that live in your digestive tract, primarily in the large intestine. A 2024 review in the Journal of Tandfonline estimates the human body contains around 100 trillion bacteria, roughly equal to the total number of human cells in the body.
This microbial community isn't just a passive passenger in your digestive system. It actively:
• Breaks down and ferments dietary fibre into short-chain fatty acids (SCFAs) — the primary fuel for the intestinal lining cells
• Produces vitamins including B12, K2 and folate
• Regulates immune function — approximately 70% of the immune system is located in and around the gut
• Communicates with the brain via the gut-brain axis, influencing mood, cognition and stress response
• Protects against harmful pathogens by competing for space and resources
• Supports metabolic function, blood sugar regulation and weight management
A diverse, well-balanced microbiome is associated with better health outcomes across nearly every body system. A disrupted microbiome — known as dysbiosis — is linked to digestive issues, weakened immunity, inflammation, mood disorders and metabolic dysfunction.
This is where prebiotics and probiotics come in.
What Are Probiotics?
Probiotics are live microorganisms that, when consumed in adequate amounts, confer a health benefit on the host. In plain English: they are beneficial bacteria (and sometimes yeasts) that you eat or supplement to directly add to the microbial population in your gut.
The term was formally defined by the World Health Organization, and the most widely studied probiotic strains belong to two primary bacterial genera:
• Lactobacillus — found naturally in fermented dairy (yoghurt, kefir), fermented vegetables (sauerkraut, kimchi), and the human gut. Different Lactobacillus species have different effects — some support digestion, some reduce lactose intolerance symptoms, some have been shown to support weight management
• Bifidobacterium — predominantly found in the large intestine. Key for fermenting fibre, producing SCFAs, supporting immune function, and protecting against harmful bacteria
Other notable probiotic organisms include Saccharomyces boulardii (a beneficial yeast particularly studied for diarrhoea prevention and gut barrier integrity) and Streptococcus thermophilus (commonly found in yoghurt).
What do probiotics do?
A 2025 comprehensive review in Frontiers in Microbiology summarised the key evidence-backed benefits of probiotic supplementation:
• Digestive health: probiotics help regulate bowel movements, reduce bloating, gas and cramping, and support the management of IBS symptoms
• Immune support: beneficial bacteria interact directly with immune cells in the gut lining, helping to regulate inflammatory responses and defence against pathogens
• Gut barrier integrity: certain probiotic strains support the tight junctions between gut lining cells, reducing intestinal permeability (sometimes called 'leaky gut')
• Mental health: via the gut-brain axis, Lactobacillus strains including L. helveticus, L. casei and L. rhamnosus have been shown to reduce psychological distress and anxiety symptoms in clinical studies
• Metabolic health: research suggests probiotics may support blood sugar regulation, reduce insulin resistance, and support weight management — particularly relevant for people on keto or low-carb diets
• Antimicrobial properties: beneficial bacteria produce compounds that inhibit the growth of harmful bacteria in the gut, protecting against infections and dysbiosis
Where do you get probiotics?
Probiotics are found naturally in fermented foods:
• Full-fat Greek yoghurt — one of the richest dietary sources of Lactobacillus and Streptococcus strains
• Kefir — a fermented milk drink with a particularly diverse probiotic profile
• Sauerkraut and kimchi — fermented cabbage dishes rich in Lactobacillus
• Tempeh — fermented soy with both probiotic and prebiotic properties
• Miso — fermented soybean paste, commonly used in Japanese cuisine
• Kombucha — fermented tea, though the probiotic content varies significantly between brands
• Aged hard cheeses — contain some live cultures, though less than yoghurt or kefir
Probiotic supplements are also widely available, offering concentrated, specific strains in capsule or powder form.
What Are Prebiotics?
If probiotics are the beneficial bacteria themselves, prebiotics are the food that feeds them.
Formally, the International Scientific Association for Probiotics and Prebiotics (ISAPP) defines a prebiotic as 'a substrate that is selectively utilised by host microorganisms, conferring a health benefit.' In practical terms: prebiotics are specific types of dietary fibre and other compounds that your body cannot digest, which pass through to the large intestine where they selectively feed and stimulate the growth of beneficial bacteria.
The term 'prebiotic' was first coined in 1995 by researchers Glenn Gibson and Marcel Roberfroid, who identified specific non-digestible carbohydrates — particularly inulin and fructooligosaccharides (FOS) — that could selectively promote the growth of Bifidobacteria and Lactobacilli.
Critically, prebiotics are selective — they feed the beneficial bacteria while having little or no effect on harmful bacteria. This selectivity is what gives them their health benefit.
The main types of prebiotics
• Inulin — found in chicory root, Jerusalem artichoke, garlic, leeks and onions. One of the most extensively researched prebiotics. Fermented by Bifidobacterium to produce SCFAs
• Fructooligosaccharides (FOS) — found in asparagus, garlic, onion, leek, banana and wheat. Like inulin, selectively feeds Bifidobacterium
• Galactooligosaccharides (GOS) — found in legumes, human breast milk. Key for early microbiome development and supporting Lactobacillus and Bifidobacterium
• Resistant starch — found in cooked and cooled potatoes and rice, green bananas, legumes. Passes through the small intestine undigested and is fermented in the large intestine, producing butyrate — a highly beneficial SCFA for gut lining health
• Pectin — found in fruit skins, particularly apple and citrus. A soluble fibre with prebiotic effects
• Acacia fibre — derived from the acacia tree, widely used in prebiotic supplements for its gentle, well-tolerated digestive effects
• Psyllium husk — a soluble fibre with both prebiotic and digestive regulatory effects. Commonly used in low-carb and keto cooking as a fibre source
What do prebiotics do?
• Feed and grow beneficial bacteria — directly increasing the population of Bifidobacterium and Lactobacillus in the gut
• Produce short-chain fatty acids — when bacteria ferment prebiotic fibre, they produce butyrate, acetate and propionate (SCFAs). Butyrate is the primary fuel for colon cells and has potent anti-inflammatory effects
• Improve stool regularity — prebiotic fibre adds bulk and draws water, supporting healthy bowel movements
• Support immune function — by promoting a healthy microbiome balance, prebiotics indirectly support the immune system housed in the gut
• Blood sugar regulation — soluble prebiotic fibres slow the absorption of glucose, reducing blood sugar spikes after meals
• Support mineral absorption — certain prebiotics (particularly inulin and FOS) have been shown to enhance calcium and magnesium absorption in the gut
Where do you get prebiotics?
Prebiotics are found in a range of plant foods, particularly those high in soluble fibre:
• Garlic, onion, leek and shallots — some of the richest prebiotic sources
• Asparagus and artichoke
• Chicory root — the richest dietary source of inulin
• Green (unripe) banana
• Legumes and beans (note: higher in carbs, use carefully on strict keto)
• Psyllium husk — popular in keto baking and as a daily fibre supplement
• Oats (not keto-friendly, but worth noting for lower-carb eaters)
• Prebiotic supplements — particularly acacia fibre, inulin powder, and FOS powders
Prebiotics vs Probiotics — What's the Actual Difference?
Here's the clearest way to think about it:
Probiotics = the bacteria themselves. Taking a probiotic supplement or eating fermented food adds live beneficial bacteria to your gut microbiome.
Prebiotics = the food for those bacteria. Consuming prebiotic fibre feeds and nourishes the beneficial bacteria already living in your gut, helping them thrive and multiply.
An analogy that helps: if your gut microbiome is a garden, probiotics are the seeds (new plants you're adding), and prebiotics are the fertiliser and water that help everything grow.
You can add new seeds without good fertiliser — but they may not survive and flourish. And you can fertilise without adding seeds — but if the soil is depleted to begin with, there may not be much to nourish. Both together tend to produce the best outcomes.
Do You Need Both? The Research on Synbiotics
The term synbiotic refers to a product or approach that combines both prebiotics and probiotics in a way that they work together synergistically — the prebiotic specifically supports the survival and activity of the probiotic.
A 2025 review published in the Journal of Clinical Medicine (PMC, 2025) evaluated the current evidence on prebiotics, probiotics, synbiotics and postbiotics, concluding that synbiotics — the combination of prebiotics and probiotics — consistently outperform either alone for improving gut microbiome diversity, intestinal barrier integrity, and immune function outcomes.
The practical implication: taking a probiotic supplement is beneficial. But if you're not also consuming adequate prebiotic fibre, many of those probiotic bacteria won't have the fuel they need to establish and thrive in your gut. They may pass through without taking up long-term residence.
Similarly, prebiotic fibre is valuable on its own — it feeds whatever beneficial bacteria are already present. But if your microbiome is significantly depleted (due to antibiotic use, illness, a highly processed diet, or chronic stress), adding prebiotics alone may not fully restore diversity.
The short answer to 'do you need both?': for most people, yes — a combination of prebiotic-rich foods, probiotic foods or supplements, and a broader gut-supportive diet delivers the best outcomes for gut health.
Gut Health and the Keto or Low-Carb Diet
This is a genuinely interesting and nuanced area. Keto and low-carb diets reduce or eliminate many of the traditional sources of prebiotic fibre — grains, legumes, high-carb root vegetables — which raises a legitimate question about gut health.
The research presents a mixed picture:
• Initial microbiome changes: studies show that starting a ketogenic diet can alter the gut microbiome within a few weeks, with some reduction in Bifidobacterium populations initially — partly because their main fuel source (fermentable carbohydrate) has been reduced
• Fat-adapted adaptation: over time, the microbiome adapts to a lower-carb environment. Research from Dr Berg (2026) and others suggests that fat-adapted keto dieters who include adequate prebiotic vegetables develop a microbiome that is different from — but not necessarily less healthy than — standard diet microbiomes
• Probiotics on keto: Dr Berg notes that probiotics promote gut microbiome diversity on keto, supporting digestion, immune defences and metabolic balance. Beneficial bacteria help regulate blood sugar balance, insulin levels and appetite-related hormones — all particularly relevant on a ketogenic diet
The practical takeaway for keto and low-carb eaters: actively including keto-friendly prebiotic foods — garlic, leek, asparagus, onion, psyllium husk, Jerusalem artichoke — and using a quality gut health supplement becomes more important, not less, when eating low-carb. Probiotic-rich fermented foods like full-fat Greek yoghurt, kefir (in moderation) and sauerkraut are all keto-compatible and worth including regularly.
For more on how to structure a low-carb diet for best results, read: What Can You Eat on a Low Carb Diet?
Signs Your Gut Microbiome Might Need Support
How do you know if your gut microbiome is out of balance? Common signs of dysbiosis (microbiome disruption) include:
• Persistent bloating, gas or abdominal discomfort
• Irregular bowel movements — either constipation or diarrhoea, or alternating between both
• Food intolerances that seem to be getting worse over time
• Frequent illness or slow recovery — a sign of compromised immune function
• Skin conditions including acne, eczema or rosacea — the gut-skin axis is real and well-documented
• Brain fog, mood changes, anxiety or low motivation — via the gut-brain axis
• Persistent fatigue despite adequate sleep
• Sugar cravings — certain gut bacteria actively signal the brain for their preferred food sources
If several of these resonate, actively supporting your gut health with prebiotic and probiotic strategies is worth prioritising. For people on keto who are also dealing with sugar cravings, there's a particularly interesting connection — read more in our guide: How to Break a Sugar Addiction
What About Postbiotics?
You may also have encountered the term postbiotics — the newest category in the gut health world. Postbiotics are the bioactive compounds produced by probiotic bacteria as they ferment prebiotics — including short-chain fatty acids (like butyrate), enzymes, peptides and vitamins.
A 2025 PMC review noted that the global market for prebiotics, probiotics and postbiotics combined was valued at over USD 57 billion in 2023, reflecting the rapidly growing scientific and consumer interest in this space.
Postbiotics are increasingly being added to gut health supplement formulas. While the research is still emerging, early evidence suggests postbiotics like butyrate may support gut barrier integrity, reduce inflammation, and benefit metabolic health.
For most people, the most practical path to postbiotic production is simply eating enough prebiotic fibre and probiotic foods — your gut bacteria will produce the postbiotics naturally.
Gut Health Products at Keto Direct 🛒
Here's a curated guide to the best gut health products from the Keto Direct range, covering both prebiotic and probiotic support:
Greens powders with prebiotic and gut health support
• Switch Nutrition Switch Greens — one of the most popular gut health products at Keto Direct. Each scoop supports energy, gut health, digestion, immunity and stress recovery. Available in Fruit Juice, Cloudy Apple, Raspberry Lemonade and Strawberry Kiwi. A brilliant daily gut health ritual for keto and low-carb eaters
• Nutra Organics Clean Greens — a comprehensive greens blend combining vegetables, prebiotics and digestive support in one daily serve
Bone broth — gut health from the inside out
Bone broth deserves a special mention in any gut health discussion. Rich in collagen, gelatin and amino acids — particularly glycine and glutamine — bone broth directly supports the integrity of the gut lining. Gelatin coats and soothes the intestinal wall, while glutamine is the primary fuel for intestinal epithelial cells. Regular bone broth consumption is one of the most traditional and effective approaches to gut health support.
• Gevity Rx Bone Broth range — including the award-winning Body Glue range. Made from premium Australian grass-fed bones, slow-cooked for maximum collagen and mineral extraction
• Nutra Organics Chicken Bone Broth Powder — Garden Herb — convenient powder format, mixes instantly into hot water for a daily gut-supportive ritual
• Best of Broth Probiotic Bone Broth — Lemon Myrtle, Papaya Leaf, Turmeric — a unique product combining the gut-lining benefits of bone broth WITH live probiotics. A genuinely functional combination
Collagen — gut lining support
Collagen is increasingly recognised as an important gut health nutrient. The amino acids glycine and proline in collagen support the integrity of the intestinal lining, reduce intestinal permeability, and support the mucosal layer that protects gut cells from damage.
• Locako Collagen Creamer — Natural — a daily keto coffee ritual that delivers gut-supporting collagen alongside MCT oil
• Chief Grass-Fed Collagen Protein Powder — Unflavoured — 100% hydrolysed grass-fed bovine collagen. Odourless, tasteless, adds to any drink or food for daily gut lining support
Functional teas with gut health support
• Steeped Digest Tea — a functional gut health tea blend, 40 serves. Designed specifically for digestive support
• Hemp Foods Australia Chai Recharge & Immunity — functional chai with hemp protein, maca and 7 spices including ginger and turmeric — both well-researched for gut health and anti-inflammatory support
• Hemp Foods Australia Drinking Chocolate — Gut Health & Immune — a functional hot chocolate formulated specifically for gut health and immune support. Zero added sugar
MCT oil — indirect gut health support
MCT oil supports gut health through a slightly different mechanism — the C10 (capric acid) fraction has demonstrated antifungal and antimicrobial properties that help maintain a healthy balance of gut bacteria. Regular MCT oil consumption is one of the reasons keto practitioners often report improvements in digestive comfort.
• Melrose MCT Oil — Kick Start 500ml — C8 and C10 blend for ketosis support and gut health
Browse the full Gut Health collection at Keto Direct at www.ketodirect.com.au.
Frequently Asked Questions
Should I take prebiotics or probiotics first?
If you're starting from scratch, many practitioners suggest beginning with probiotics to introduce beneficial bacteria, then adding prebiotic fibre to feed them. In practice, most people do well taking both simultaneously — either as a synbiotic supplement or by eating probiotic foods and prebiotic-rich vegetables together. There's no strict rule here.
Can you take too many probiotics?
For most healthy people, probiotic supplements are well-tolerated. Some people experience temporary bloating, gas or digestive changes when starting probiotics — this usually settles within a week or two as the gut adjusts. People who are immunocompromised, critically ill, or have certain medical conditions should consult their doctor before starting probiotics.
Do probiotics survive stomach acid?
Some do, some don't. This is a key quality consideration when choosing probiotic supplements. Look for products with enteric coating, delayed-release capsules, or strains that are specifically documented for acid resistance. Alternatively, taking probiotics with food slows gastric emptying and improves survival. Lactobacillus and Bifidobacterium strains vary significantly in acid tolerance — always check the manufacturer's research.
How long does it take for probiotics to work?
Most people notice some digestive improvements within 2-4 weeks of consistent probiotic use. More significant microbiome changes take longer — typically 4-8 weeks of consistent supplementation alongside a prebiotic-rich diet. Results vary significantly between individuals based on the starting state of the microbiome, diet, stress levels and antibiotic history.
Are prebiotics keto-friendly?
Many prebiotic food sources are high in carbohydrates (oats, bananas, legumes) and are not suitable for strict keto. However, there are plenty of keto-compatible prebiotic sources: garlic, leek, asparagus, onion, psyllium husk, Jerusalem artichoke (in small amounts), and chicory root. Prebiotic fibre supplements like acacia fibre and inulin are typically used in small enough amounts that they don't significantly impact net carbs.
Is bone broth a probiotic?
Standard bone broth is not a probiotic — it doesn't contain live bacteria. However, it supports gut health through a different mechanism: the collagen, gelatin and amino acids in bone broth directly nourish and repair the gut lining. Some bone broth products — like the Best of Broth Probiotic Bone Broth available at Keto Direct — add live probiotic cultures to bone broth, combining both benefits in one product.
What is the gut-brain axis?
The gut-brain axis is the bidirectional communication network between the gut microbiome and the central nervous system, operating through the vagus nerve, the immune system, and gut-produced neurotransmitters (including serotonin — approximately 90% of the body's serotonin is produced in the gut). Research consistently shows that the state of the gut microbiome influences mood, cognitive function, stress response and mental health — and vice versa.
Final Thoughts
The gut microbiome is arguably the most exciting area of nutritional science right now — and the research on prebiotics and probiotics is giving us genuinely actionable tools for supporting it.
Do you need both? For most people, yes. Probiotics introduce and replenish beneficial bacteria; prebiotics feed and sustain them. Together, they create the conditions for a diverse, resilient gut microbiome that supports your digestion, immunity, energy, mood and metabolic health.
The good news is that most of the most powerful gut health strategies don't require expensive supplements. Eating fermented foods regularly, including prebiotic vegetables in your meals, staying well-hydrated, managing stress, getting adequate sleep, and incorporating bone broth and collagen — these are the foundations. Quality supplements from Keto Direct can complement and accelerate that foundation.
Your gut does a lot for you. It's worth taking care of it. Browse the full gut health range at www.ketodirect.com.au/collections/gut-health.
🛒 Shop Gut Health Products → www.ketodirect.com.au/collections/gut-health
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