Why plants matter for your microbiome
Your gut contains a vast community of microorganisms, often referred to as the gut microbiome, that help to break down food components we cannot digest ourselves, support the gut lining and interact closely with the immune system. One of the most consistent findings in microbiome research is that people who eat a wide variety of plant foods tend to have a more diverse microbiome. This matters because microbial diversity is considered one indicator of a stable and resilient gut environment.
Plants are packed with components such as dietary fibres, resistant starches and polyphenols. These pass through the upper digestive tract largely intact and become ‘food’ for our gut bacteria. The microbiome then ferments these compounds which produces short-chain fatty acids (SCFAs), which are known to play roles in maintaining gut barrier function and supporting anti-inflammatory pathways.
While research is ongoing, large population studies such as the American Gut Project, have shown that participants who consumed more than 30 different plant foods per week had significantly greater microbial diversity compared with those eating fewer than 10 varieties. This supports the idea that a diet rich in varied plant foods is a practical, food-first approach to support a diverse and balanced gut microbiome, without requiring strict dietary patterns.
What “plant-based” really means
The term plant-based is widely used, but it doesn’t necessarily mean vegetarian or vegan. In practice, a plant-based pattern simply means that plants make up the majority of the diet, while still allowing room for animal products if someone chooses to include them. Below is a summary of the main dietary patterns often grouped under the wider “plant-based” umbrella, and how they differ:
- Vegan: A vegan diet excludes all animal-derived foods. It can meet nutritional needs when carefully planned but requires attention to nutrients such as vitamin B12, iodine, calcium and iron, which are less reliably obtained from plant foods alone.
- Vegetarian: Vegetarian diets exclude meat and fish but include foods such as dairy or eggs. These diets can offer many of the benefits of plant-focused eating while providing additional sources of protein and micronutrients.
- Plant-based (non-vegan): This approach prioritises plant foods, vegetables, fruits, wholegrains, legumes, nuts and seeds, while still incorporating animal products in smaller or flexible amounts. Many people find this a sustainable and practical way to increase plant diversity without committing to full exclusion of animal products.
Across all of these dietary choices, it is the range and variety of plant foods that appear most relevant to supporting microbial diversity, rather than strict dietary labels.
Personal tolerance matters
While increasing plant diversity is generally beneficial, some people, particularly those with conditions such as IBS, or with naturally more sensitive digestion, may find certain foods less comfortable. Many plants contain fermentable carbohydrates known as FODMAPs (Fermentable Oligo-, Di- and Mono-saccharides and Polyols). These are types of short-chain carbohydrates that are more readily fermented by gut bacteria, which can lead to symptoms such as bloating or abdominal discomfort in some individuals. These foods are not harmful in themselves, but tolerance varies widely. Portion size, preparation and the pace of dietary changes all influence comfort.
If symptoms are persistent or disruptive, it is advisable to seek guidance from a registered dietitian, who can help explore potential triggers and ensure dietary changes remain varied, balanced and appropriate.
Why plant diversity supports gut health
A consistent theme across microbiome research is that dietary variety influences the composition and resilience of the gut microbiome. Different bacterial species thrive on different substrates, meaning no single plant food can support the full range of microbes living in the gut. When the diet includes a range of plant foods, it provides a wider selection of fibres and plant compounds that can be used by many different microbes.
Large-scale observational work, including findings from the American Gut Project, has shown that individuals consuming more than 30 different plant foods per week tended to have greater microbial diversity than those eating fewer than 10. These studies are described as observational because they look at patterns in large populations rather than testing a specific intervention. This means they cannot prove one factor directly causes another, but they can highlight strong associations and, in this case, that people with more varied plant intake also had more diverse gut bacteria. Observational data of this scale help researchers identify meaningful dietary patterns that may contribute to gut health.
Increasing plant diversity also naturally raises the likelihood of consuming a mixture of soluble and insoluble fibres, resistant starches, polyphenols and other bioactive compounds. Each of these interacts with the gut in slightly different ways, supporting regularity, influencing fermentation processes or contributing to the production of beneficial metabolites, together creating a dietary environment associated with positive gut health markers.
Fibre types (soluble, insoluble, resistant starch)
Because different plant foods provide different substrates for gut bacteria, it can be helpful to understand the main types of fibre they contain. Fibre isn’t a single nutrient, but a collective term for several compounds that each interact with the gut in slightly different ways.
Soluble fibre
Found in foods such as oats, apples, beans and many fruits. It absorbs water to form a gel-like texture and is readily fermented by gut bacteria. Soluble fibre contributes to softer stools and supports steady digestion.
Insoluble fibre
Present in wholegrains, nuts, seeds and the skins of fruits and vegetables. It adds bulk to stools and supports regular bowel movements. Insoluble fibre is less fermentable but still important for overall digestive function.
Resistant starch
Found in legumes, wholegrains, green bananas and cooked-then-cooled starchy foods like potatoes or rice. Resistant starch reaches the colon intact and becomes a key fuel source for certain beneficial bacteria.
Including a mixture of these fibres across the week is a practical way to support both digestive function and microbial activity.
Prebiotics, polyphenols and products containing live bacteria
Alongside fibre, plants contain other compounds that can influence microbial activity, including prebiotics, probiotics and polyphenols. Although often used interchangeably, they refer to distinct components, and understanding the differences can help clarify how they collectively contribute to the diet-microbiome relationship.
Prebiotics are specific types of fermentable fibre that act as a food source for certain beneficial gut bacteria. They occur naturally in foods such as onions, garlic, leeks, chicory, legumes and some fruits. When tolerated, they complement other dietary fibres by providing additional substrates for microbial fermentation.
Probiotics, by contrast, are live microorganisms consumed through foods or products. Unlike prebiotics, which feed bacteria already present, probiotics introduce new live bacteria into the diet. Fermented foods may contain live cultures but some people choose to take a probiotic supplement which delivers defined strains and controlled doses to the gut.
Symprove is one example of a water-based supplement containing live and active bacteria, used by some individuals alongside a diet that emphasises plant diversity and fibre.
Polyphenols are naturally occurring plant compounds found in foods such as berries, herbs, spices, cocoa, tea and colourful vegetables. Many reach the large intestine intact, where they are metabolised by gut bacteria into smaller compounds associated with favourable gut health markers. While not fibres or live bacteria themselves, polyphenols add further variety to the substrates and signals available to the microbiome and contribute to the wider health benefits associated with eating a diverse range of plant foods.
Fermented Foods and Live Cultures
Fermented foods are created when microorganisms such as bacteria or yeasts break down carbohydrates in food, producing acids or alcohols that alter flavour, texture and preservation. Depending on how they are made, many fermented foods still contain live cultures at the point of consumption. These live cultures are not the same as probiotic supplements as fermented foods contain naturally occurring mixes of microbes and fermentation by-products rather than defined strains in controlled doses, but they do contribute to dietary variety and microbial exposure.
Common examples of fermented foods include kefir, kimchi, kombucha, sauerkraut and cultured dairy products such as live yogurt. The specific microorganisms present will vary between foods and production methods, but these products remain an accessible way to add diversity to the diet.
Fermentation also produces a range of non-living microbial components and metabolites, known as postbiotics. Sometimes referred to informally as “zombie biotics,” these are no longer alive but may still interact with the gut environment and have positive effects. Postbiotics occur naturally in traditionally fermented foods and form part of the overall mix of compounds produced during fermentation.
Recent observational work supports interest in fermented foods. A large 2025 study involving adults who increased their fermented food intake for two weeks reported associations with improvements in self-reported bloating, mood, energy and hunger levels. While these findings cannot confirm cause and effect, they highlight that incorporating fermented foods may have noticeable day-to-day effects for some people, with individual tolerance varying. For most individuals, fermented foods can be an enjoyable and practical addition to a plant-rich diet, providing flavour, culinary variety and an additional source of live microbes and fermentation by-products.
Easy ways to reach 30 plants a week
While reaching 30 different plant foods a week sounds overwhelming, it is often easier than people expect. Fruits, vegetables, wholegrains, legumes, nuts, seeds, herbs and spices, and >70% (cocoa solids) dark chocolate all count individually, so small additions quickly add up!
Below are some top tips to help with this:
Breakfast add-ins:
- Add berries, sliced fruit or grated vegetables to porridge or yogurt
- Stir in chia seeds, flaxseed, mixed nuts or pumpkin/sunflower seeds into your breakfast
- Blend spinach, oats or nut butter into smoothies
- Choose wholegrain or seeded bread to naturally increase plant variety
Lunch and dinner swaps:
- Add lentils or beans to soups, stews, chillies or pasta sauces
- Combine wholegrains (quinoa, bulgur, barley) with vegetables and legumes for bowls or salads
- Add an extra vegetable to any dish - fresh, frozen or tinned all count
- Use herbs, spices, miso, tahini or other flavours to boost plant diversity with minimal effort
For those managing IBS or gut sensitivity, certain plant foods are often better tolerated and may help people maintain variety while supporting comfort. Individual responses vary, so guidance from a dietitian can be helpful. Examples include:
- Vegetables: carrots, courgette, peppers, spinach, aubergine
- Fruits: berries, grapes, citrus
- Grains: oats, brown rice, quinoa
- Proteins: firm tofu, tempeh, nuts and seeds
- Extras: small amounts of chia or flaxseed
Key nutrients to consider
A well-planned plant-rich diet can meet most nutritional needs, but a few nutrients may require closer attention depending on how much (or how little) animal food someone includes. The nutrients below are particularly relevant for those following predominantly plant-based patterns and may be useful tips if you are doing Veganuary this year!
Protein sources that are gut-friendly
Plant proteins bring the added benefit of fibre and various phytochemicals. Useful options include:
- Lentils, chickpeas and beans - start with smaller portions if you’re building tolerance.
- Tofu, tempeh and edamame - often well tolerated and versatile.
- Nuts, seeds and nut butters - providing protein, healthy fats and micronutrients.
- Wholegrains such as quinoa, buckwheat and farro, which contribute both protein and fibre.
Iron, calcium and B12.
Iron: found in lentils, beans, wholegrains, nuts, seeds and fortified cereals. Pairing plant iron sources with vitamin C-rich foods (such as peppers or citrus fruits) which can help support absorption of iron from plant-based foods.
Calcium: found in calcium-set tofu, tahini, almonds, chia seeds, and fortified plant milks and yogurts.
Vitamin B12: not naturally present in plant foods. Those following vegan diets should include B12-fortified foods or consider supplements in line with UK guidance.
Managing common symptoms
Increasing plant intake is generally positive, but it can bring short-term digestive changes and symptoms as the gut adapts. Small adjustments to pace and preparation can make a big difference, and below are some top tips to help manage common symptoms.
Bloating:
- Increase fibre gradually over several weeks rather than making a sudden overnight change
- Start with smaller portions of legumes and build up slowly
- Ensure you drink plenty of water to support digestion when fibre intake increases
- Eat slowly and chew thoroughly to reduce swallowed air
Intolerances and what to swap:
- Some people find certain plant foods more symptomatic than others:
- Legumes: canned beans, red lentils or tempeh are often good starting points
- Brassicas: if broccoli, cauliflower or cabbage trigger discomfort, try carrots, green beans, peppers, courgette or spinach instead
- Cooked vegetables are often better tolerated than raw
When to seek advice:
If symptoms persist or become disruptive, it’s important to speak with a GP to rule out underlying conditions. A registered dietitian can provide tailored guidance on symptom management, food reintroduction and strategies for meeting nutritional needs while managing comfort.
FAQs
Is a plant-based diet better for gut health?
Not always. However, diets that include a wide variety of plant foods are consistently associated with greater microbial diversity. You don’t need to exclude animal products to benefit.
How do I actually get 30 different plants a week?
Count everything: fruits, vegetables, wholegrains, nuts, seeds, legumes, herbs and spices. Adding one or two extra plant foods to meals makes the total rise quickly.
Why does a plant-based diet sometimes cause bloating?
A sudden increase in fibre or fermentable carbohydrates can create more gas as gut bacteria adapt. Making changes gradually and adjusting portions often helps.
What fermented foods should I eat in the UK?
Live yoghurt, kefir, kombucha, kimchi, sauerkraut, miso and tempeh are widely available and easy to include in everyday meals.
What if I can’t tolerate beans or lentils?
Start with small amounts, try canned varieties or red lentils, and consider gentler alternatives such as tofu, tempeh, quinoa, nuts or seeds.
How can I support iron, calcium and B12 on a mostly plant-based diet?
Use fortified foods where appropriate, pair iron-rich foods with vitamin C, include calcium-set tofu and fortified plant milks, and use B12-fortified foods or supplements if following a vegan diet.
To learn more about other gut health topics, visit Symprove’s Gut Hub.
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