Which foods help transit?

According to ameli, fibre helps increase stool frequency and makes stools softer: fruit and vegetables, wholegrain cereals, dried pulses and dried fruit, with a gradual increase over two weeks to reach at least 25 g a day, and at least 1.5 litres of fluid a day in the absence of medical contraindication. If constipation persists, consult a doctor.

Are probiotics allowed on labels in Europe?

Under the European Ombudsman's decision of 20 December 2024, the Commission rejected all applications for health claims on probiotics following negative EFSA opinions, and considers that the term "probiotics" is itself a health claim. The word is therefore rare on food products.

Are fermented foods good for the gut?

The evidence is limited. A 2019 review concludes that the clinical evidence for most fermented foods is very limited; kefir is the best studied, with a possible benefit on lactose absorption, and no randomised trial has evaluated kimchi. They can fit into a varied diet, with no proven effect.

Can a food boost immunity?

No food guarantees it. European regulation allows the statement that certain nutrients, including vitamin C, vitamin D, zinc and selenium, contribute to the normal function of the immune system, provided the food is a source of them. If symptoms persist or infections recur, seek medical advice.

Digestion and immunity: friendly foods

What food can (and cannot) do

Comfortable digestion, "natural defences", gut flora: the subject attracts many promises. This article takes stock of what official sources say and points out what remains uncertain. No food "boosts" immunity on its own, and this guide does not replace a doctor's advice.

Transit: fibre and fluids

For constipation in adults, Assurance maladie (ameli) states that fibre helps increase stool frequency and makes stools softer. It advises increasing intake gradually over two weeks, to reach at least 25 g a day and avoid pain and bloating, with fruit and vegetables, wholegrain cereals, dried pulses and dried fruit. It also recommends drinking at least 1.5 litres a day (water, soups, herbal teas), in the absence of medical contraindication.

The WHO, for its part, sets at least 400 g of fruit and vegetables a day and at least 25 g of fibre for an adult. ANSES and EFSA do not have exactly the same benchmark, which is detailed inFoods rich in protein and fibre, with the contents of the main foods.

Hydration

ANSES recommends that adults drink a minimum of 1.5 to 2 litres of water a day, even before feeling thirsty. This benchmark applies to the whole day; it is not a cure: drinking more does not guarantee better transit or better immunity, and we have found no official source that claims it.

The gut microbiota: what are we talking about?

According to Inserm, a microbiota is the set of micro-organisms (bacteria, viruses, parasites, non-pathogenic fungi) living in a given environment. The gut microbiota is the most populous in the body and is found mainly in the small intestine and the colon. It is specific to each individual, develops from birth and contributes to digestion, nutrient absorption, vitamin synthesis and intestinal immunity.

Inserm also stresses the limits: an imbalance of the microbiota (dysbiosis) can be both a cause and a consequence of diseases, and the direction of these links is still barely described. It notes that fibre fuels the microbiota, that the impact of additives and pesticides on its composition is possible but without firm conclusion, and that avenues of personalised nutrition still need to be confirmed.

Fermented foods: limited evidence

Yoghurt, kefir, raw sauerkraut, kimchi: these foods contain live micro-organisms, and they are readily credited with virtues. A 2019 review published in Nutrients nevertheless concludes that the evidence for digestive health is "very limited" for most fermented foods.

Kefir: it is the best studied food. At least one randomised trial suggests a possible benefit for lactose malabsorption.
Kimchi: no randomised trial has, to date, evaluated its effect on digestive health.
Yoghurt: the review does not assess it, as it has already been widely studied elsewhere.

Another review (Journal of Nutrition, 2020) estimates that fermented foods can alter certain bacterial populations in the gut, but calls for longer and larger studies to confirm these results and show that they are of benefit to health. Fermented foods can therefore find their place in a varied diet, without any proven effect being attributed to them.

Probiotics: why packaging remains cautious

Probiotics are live micro-organisms supposed to bring a benefit to the host. On the European regulatory side, the Commission rejected all applications for authorisation of health claims on probiotics, following negative scientific opinions from EFSA, according to the European Ombudsman's decision of 20 December 2024. The Commission also considers that the term "probiotics" is itself a health claim, which explains why the word is rare on food products sold in Europe.

Inserm notes on its side that classic probiotic trials have been "inconclusive", and that research is turning to new candidates. This does not mean that probiotics are useless, but that no general benefit is officially recognised for everyday diet.

Regulation (EU) No 432/2012, by contrast, authorises a claim on yoghurt cultures, which is not a probiotic claim: live cultures of yoghurt or fermented milk (at least 10 to the power of 8 live bacteria per gram) improve lactose digestion in people who have difficulty digesting it.

Prebiotics: a precise definition

According to the ISAPP expert consensus (2017), a prebiotic is "a substrate selectively used by host microorganisms conferring a health benefit". Inserm describes them as foods specific to the microbiota; the definition requires a health benefit, not just fermentation.

Immunity: what authorised claims say

European Regulation 432/2012 lists the authorised health claims on foods. It notably includes that vitamin C, vitamin D, zinc and selenium (like vitamins A, B6, B12, folates, copper and iron) "contribute to the normal function of the immune system" (translation of the English wording), provided the food is at least a source of the nutrient concerned. In other words: these nutrients are necessary for normal functioning. This does not mean that consuming more of them would make the body more resistant. EFSA assesses the scientific basis of claims, but does not decide on their authorisation.

Food sources are detailed inFoods rich in vitamins C and D and omega-3andFoods rich in iron, zinc and magnesium. A wording such as "strengthens natural defences" is also a claim subject to authorisation.

Ultra-processed foods and additives: where do things stand?

The precise link between ultra-processed foods and digestion is still being studied.Ultra-processed foods: how to recognise them and which to avoidsummarises the cautious opinion of ANSES (January 2025): an association with health risks, with weak weight of evidence.

On emulsifiers,Additives: are they all a real danger?cites an observational study from the NutriNet-Santé cohort (Inserm, 2024, about 92,000 adults) which links certain emulsifiers to a higher risk of cancer. This is an association, not proof of causation. Carrageenans are also debated for their effect on the gut. On Yumiq, the product page shows the number of additives detected (harmless, to watch or risky), and the Yumiq-Score penalises controversial additives assessed by EFSA and ANSES.

Common myths: detox, cures and juices

"Detox cures" and juices supposed to "cleanse" the gut do not appear in any of the official benchmarks we consulted (ameli, ANSES, WHO), which favour a varied diet with fruit, vegetables, legumes and wholegrain cereals. According to Allodocteurs, the concept of "toxins" has no medical meaning. A juice does not replace a whole fruit either: we have no official source to precisely compare their effects on digestion, so it is best to stick to general benchmarks.

When to see a doctor

According to ameli, you should see your doctor if constipation persists despite dietary measures, or if it is recent and significant after the age of 50. A prompt consultation is advised in case of fever or severe abdominal pain, and call 15 or 112 in case of vomiting, abdominal pain and inability to pass wind. Any digestive symptom that lasts warrants medical advice: food does not replace a diagnosis.

To remember

Fibre, fruit, vegetables, legumes and water are the solid benchmarks for transit.
The microbiota is an active research topic: many links remain to be confirmed.
The evidence on fermented foods is limited, and no probiotic claim is authorised in the EU.
Several nutrients, including vitamins C and D, zinc and selenium, contribute to the normal function of the immune system, with no proven "booster" effect.
No miracle food: variety, minimally processed products, medical advice in case of persistent symptoms.