Gut & microbiome

Gut flora, fibre and fermented foods.

66 answers, from 437 studies

Last updated: July 2026

Key questions

There is no universal daily dose for probiotics: how much you need depends strongly on the bacterial strain, the application,…

Moderate evidence

Can probiotics improve your health in later life?

Clinical studies into probiotics and ageing are ongoing, but results are not yet available. At this point there is too little…

Insufficient evidence

Does eating a varied diet help your gut bacteria?

Fermented products have the strongest evidence base for increasing gut bacterial diversity. Eating broadly varied meals also…

Yes · Moderate evidence

Is fibre-maxxing (eating as much fibre as possible) healthy?

Eating more fibre is a good idea for most people in the West, but fibre-maxxing as an extreme principle offers no additional…

Yes · Moderate evidence

Can you strengthen your immune system by eating more fibre?

Extra fibre turns out to strengthen the immune system in healthy people less clearly than expected; fermented foods currently…

Preliminary evidence

What does the transition into menopause do to your gut microbiome?

Menopause noticeably changes your gut microbiome: less diversity, weaker reactivation of oestrogen and a slightly more…

Can you improve your gut flora by picking up bacteria while playing outdoors?

There is no evidence that playing outside or contact with soil measurably improves your gut flora. If you want to support your…

No · Preliminary evidence

Can you see how fast you are ageing from your stool?

Your microbiome does change with age and is associated with health risks, but a reliable ageing test based on stool does not…

Moderate evidence

Are the gut bacteria of children different from those of adults?

Yes, the gut bacteria of children differ fundamentally from those of adults, with consequences for allergy and asthma risk. If…

Can an unhealthy gut contribute to skin problems such as acne or eczema?

A disrupted gut microbiome is associated with acne and eczema, although that association has not yet been proven to be cause…

Does chewing slowly really help with better digestion?

There is no direct evidence that chewing more slowly improves digestion in healthy people. The association between poor…

Insufficient evidence

What does drinking coffee every day do to your gut bacteria?

Drinking coffee in moderation every day (up to 4 cups) is associated with a more favourable composition and greater diversity…

Can your gut flora influence your memory and concentration?

Your gut flora very likely does influence memory and concentration, but the evidence in humans is still limited. A varied diet…

What is the role of bile acids in healthy digestion?

Bile acids are indispensable for fat digestion, the absorption of vitamins A, D, E, and K, and a healthy cholesterol balance.…

What does smoking do to your gut and gut microbiome?

Smoking disrupts your gut microbiome and increases the risk of intestinal inflammation, gastrointestinal complaints and…

Does bone broth help your gut health?

The individual components of bone broth, such as certain amino acids, show favourable effects on the intestinal wall in…

Preliminary evidence

Can your gut microbiome influence inflammation in your body?

Your gut microbiome can influence inflammatory processes throughout your body via the gut wall. Eating more fibre and…

Does your gut microbiome affect how well you sleep?

Your gut microbiome and your sleep mutually influence each other, but how to practically steer that through probiotics or…

Are the gut bacteria of lean people different from those of heavier people?

The gut bacteria of people with excess weight differ measurably from those of lean people, but whether those bacteria are the…

What does a high-fat diet do to your gut microbiome?

A high-fat diet noticeably disrupts the gut microbiome: less bacterial diversity, more harmful species and a leaky gut wall…

Can you improve your gut bacteria by spending more time in nature?

Whether spending more time in nature improves your gut bacteria is a question the available studies cannot answer; if you want…

Preliminary evidence

Can certain fungi or bacteria in your gut influence your cellular ageing?

Yes, certain gut bacteria and their metabolic by-products can accelerate cellular ageing, but most of the evidence still comes…

Does drinking apple cider vinegar help your digestion?

There is no research whatsoever showing that apple cider vinegar improves digestion. If you want to use apple cider vinegar…

No · Preliminary evidence

Can your gut microbiome control your appetite and hunger?

Your gut microbiome influences your appetite through hormones, nerve signals and substances produced from fibre fermentation.…

What does eating too much sugar do to your gut health?

Eating a lot of sugar probably disrupts your gut microbiome and makes the gut wall more permeable, but it is the combination…

Does a healthy gut microbiome lead to better skin?

There is clear evidence suggesting that a balanced gut flora contributes to healthier skin, but the evidence is still…

Yes · Preliminary evidence

Does eating flaxseed help your gut?

Flaxseed has biologically plausible effects on the gut, but evidence in humans is scarce and mixed. Fine to eat as part of a…

Preliminary evidence

Do gut problems play a role in poor bone formation?

A disrupted gut microbiome can contribute to poor bone formation through inflammation, reduced calcium absorption and…

Can your gut microbiome influence your risk of heart disease?

Your gut microbiome influences your heart health through metabolic by-products that can promote arterial hardening, high blood…

Yes · Moderate evidence

Can your microbiome reveal how old you are biologically?

Your gut microbiome demonstrably changes with the years and is associated with healthy ageing, but as a biological age marker…

Is the appendix actually useful for your gut microbiome?

The appendix does appear to serve a purpose: as a bacterial reservoir for your gut microbiome and as a production site for…

What does fasting one day a week do to your gut microbiome?

Intermittent fasting demonstrably changes your gut microbiome, but the effects are likely temporary if you stop; for healthy…

Can your gut microbiome affect your cholesterol?

Your gut microbiome influences your cholesterol through bile acid conversion and the fermentation of fibres. Eating more fibre…

Does eating gluten-free help if you don't have coeliac disease?

If you do not have coeliac disease, a wheat allergy, or confirmed gluten sensitivity, eating gluten-free provides no proven…

No · Preliminary evidence

What do polyphenols, such as those found in berries and red wine, do to your gut bacteria?

Polyphenols from berries, wine and vegetables demonstrably shift your gut microbiome in a favourable direction and are…

Are plant-based diets better for your gut than mixed diets?

Plant-based eating is good for your gut bacteria, but a Mediterranean diet combined with fermented foods performs at least as…

Moderate evidence

Does fermented food like kimchi boost your immune system?

Fermented foods such as kimchi show early positive signs for a healthier gut microbiome and lower inflammatory markers, but…

Preliminary evidence

Can exercise improve your gut microbiome?

Moderate regular exercise demonstrably improves your gut microbiome, but you need to keep exercising because the effect…

Yes · Moderate evidence

What are the signs that your gut microbiome is out of balance?

A disrupted gut microbiome manifests as reduced bacterial diversity, mood complaints, skin problems, and a leaky gut wall, but…

Does green tea help your gut health?

Green tea likely has a modest positive effect on gut bacteria, but this has not yet been firmly proven in humans. It fits well…

Preliminary evidence

How does your gut microbiome influence your hormone balance?

Your gut microbiome drives multiple hormones through enzymes, fermentation products and bile acids, ranging from oestrogen to…

What does too little sleep do to your gut?

Too little sleep demonstrably disrupts the composition of your gut bacteria and lowers butyrate, a substance that helps…

Are stomach pain and bloating signs of an unhealthy gut?

Stomach pain and bloating can point to several gut complaints, not just an 'unhealthy' gut. Have your symptoms properly…

What does alcohol do to your gut microbiome?

Chronic heavy drinking demonstrably disrupts the gut microbiome, with consequences for the heart and liver. Moderate drinking…

Does intermittent fasting help your gut health?

Intermittent fasting likely improves your gut flora and gut barrier in the short term, but it remains unclear whether those…

Yes · Moderate evidence

Is irritable bowel syndrome a real condition, or is it all in your head?

IBS is a recognised physical condition with measurable biological abnormalities, not a figment of the imagination. If you are…

Can stress really make your gut sick?

Stress disrupts your gut microbiome and increases the risk of gut complaints such as irritable bowel syndrome, but the precise…

What is the difference between probiotics and postbiotics?

Postbiotics appear to work just as well as live probiotics for irritable bowel syndrome and are safer in people with a…

Does eating garlic help your gut health?

Garlic has interesting but not yet sufficiently proven effects on gut bacteria. If you do not have irritable bowel syndrome,…

Preliminary evidence

What does eating red meat do to your gut over the long term?

Consistently eating large amounts of red meat is associated with a less diverse gut microbiome and a higher risk of colorectal…

What does alcohol do to your immune system?

Heavy or prolonged alcohol use clearly weakens your immune system and increases the risk of serious infections and liver…

Can your gut microbiome influence how long you live?

There is consistent evidence suggesting that a diverse, anti-inflammatory gut microbiome is associated with healthy and long…

Moderate evidence

Is my gut flora linked to being overweight?

Your gut microbiome is probably linked to excess weight through multiple mechanisms, but a proven causal relationship in…

Does eating a high-fibre diet help against constipation as you get older?

Eating more fibre is no guarantee against constipation and can even be counterproductive in cases of persistent symptoms; a…

Moderate evidence

Does my gut microbiome change as I get older, and does it matter?

Yes, your gut microbiome changes measurably with age, but whether that matters depends strongly on your diet and lifestyle. A…

Yes · Strong evidence

Does leaky gut actually exist?

Leaky gut is a recognised biological phenomenon that is associated with various diseases, but whether it also causes those…

Do prebiotics, the fibres that feed your good bacteria, work just as well as probiotics?

Prebiotics alone are less effective than probiotics in the best-studied situations. For diarrhoea or immune support,…

No · Moderate evidence

What do artificial sweeteners do to your gut microbiome?

Whether artificial sweeteners truly disrupt your gut microbiome is not yet clear: studies contradict one another. Until there…

Can you restore your gut microbiome after a course of antibiotics?

Your gut microbiome partially recovers after a course of antibiotics, but a full return to its original state is rarely…

Moderate evidence

Can a disrupted gut microbiome weaken your immune system?

A disrupted gut microbiome demonstrably dysregulates your immune system and increases the risk of chronic inflammation. Eating…

Yes · Moderate evidence

Is there a real connection between your gut microbiome and your mood or brain?

There is a biologically plausible and, in animal research, robustly supported connection between your gut microbiome and your…

Does fermented food such as yoghurt, kefir and sauerkraut help your gut microbiome?

Fermented foods, and kefir and yoghurt in particular, have the strongest clinical support for a positive effect on the gut…

Yes · Moderate evidence

What does eating fibre do to your gut microbiome and your long-term health?

Fibre demonstrably feeds your gut bacteria, improves stool consistency and protects the gut wall. But how your microbiome and…

Do probiotic pills actually help your gut?

Probiotics demonstrably help with specific complaints such as rotavirus diarrhoea and pouchitis, but are not a general gut…

Yes · Moderate evidence

Are fermented foods and probiotics good for your gut?

Fermented foods, particularly yoghurt and kefir, show positive indications for gut health; for most other products such as…

Yes · Moderate evidence

Are at-home microbiome tests worthwhile?

Microbiome home tests are not yet sufficiently scientifically substantiated for meaningful use in diagnostics or prevention,…

No · Preliminary evidence

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