Eating against silent inflammation

What is on your plate influences how agitated your immune system is.

How solid is the research? Promising

For the Mediterranean diet there are controlled studies with favourable effects on inflammatory markers; for fermented foods, see the separate chapter. The harm caused by additives has only begun to be studied in humans.

Cause or consequence? Cause and consequence

Inflammation comes from a leaky barrier and inflamed gums. It is usually a consequence — and then works on into fatigue and skin.

Healthy state

“Silent inflammation” does not mean an inflammation you feel, but a permanently slightly raised activity of the immune system that shows up only in blood values such as CRP or certain messenger substances. The term is vague and not a diagnosis. Still, the idea holds up: a large part of the immune system sits in the gut, and what arrives there sets its baseline.

The most important bridge is fibre. What the small intestine and its enzymes cannot break down reaches the colon and is fermented there by bacteria into Short-chain fatty acids Acids such as acetate, propionate and butyrate that gut bacteria make from fibre. They nourish the gut wall and act throughout the body. More in the chapter “Butyrate and other short-chain fatty acids”, mainly acetate, propionate and Butyrate A short-chain fatty acid and the main energy source for the cells of the colon wall. It strengthens the barrier and dampens inflammation. More in the chapter “Butyrate and other short-chain fatty acids”. Butyrate is the preferred fuel of the cells lining the colon, supports the Mucus layer A gel layer of mucins on the gut wall that keeps bacteria at a distance. In the colon, the inner layer is almost free of microbes. More in the chapter “The mucus layer and additives” and the Tight junctions Protein connections that hold the cells of the gut wall tightly together. They determine what can pass between the cells. More in the chapter “The gut barrier” between cells, and helps form regulatory T cells that calm the immune system. The more varied the plant food, the more different bacteria find food and the more stable this chain runs. More in the chapter on short-chain fatty acids.

Then there are polyphenols, the colour and bitter compounds in berries, vegetables, herbs, coffee, tea, olive oil and dark chocolate. Only part is absorbed in the small intestine; the rest travels on to gut bacteria, which turn it into smaller, more active substances. Fats count too: olive oil and oily fish provide unsaturated fatty acids from which the body makes inflammation-resolving messengers, while an excess of saturated fat and alcohol rather strains the barrier.

The Mediterranean diet bundles these building blocks. In the NU-AGE study, older people in several European countries ate in this pattern for a year. The Microbiome, gut microbiota The community of all microbes in the gut, mainly bacteria, plus viruses, fungi and archaea. Most live in the colon. More in the chapter “Building microbial diversity” shifted towards more butyrate-producing bacteria, and inflammatory markers moved in the favourable direction. That does not mean a single ingredient works; it is the whole pattern of plenty of plant foods, little processed food and good fats. The immune system in the gut stays alert but calm that way: it recognises real dangers and does not react to every food component.

Plant variety and fibre feed the bacteria that dampen inflammation.

Disrupted state: causes and effects

On the other side is what researchers call “ultra-processed foods”. These are industrial products made from broken-down ingredients with additives such as Emulsifiers Additives that mix fat and water, such as carboxymethylcellulose or polysorbate 80. Some damage the mucus layer in studies. More in the chapter “The mucus layer and additives”, sweeteners, flavourings and thickeners, for example soft drinks, bars, ready meals, sausage products or breakfast cereals. The term is broad and not entirely uniform: an industrial wholemeal bread can fall into it, while a home-cooked dish with lots of sugar does not. The studies therefore lump very different things together.

What they show: in a feeding study by the US health agency, 20 adults ate an ultra-processed and an unprocessed diet for two weeks each, both composed to offer the same nutrients on paper. On the ultra-processed diet they ate about 500 kilocalories more per day, ate faster and gained weight. In a large observational study of more than 116,000 adults in 21 countries, the risk of Inflammatory bowel disease Umbrella term for Crohn’s disease and ulcerative colitis: long-term, relapsing inflammation of the gut that needs medical treatment. More in the chapter “Immune system and inflammation” at five or more servings a day was clearly higher (hazard ratio 1.82) than at fewer than one, mainly for soft drinks, sweets, salty snacks and processed meat; meat, dairy, fruit and vegetables showed no such link. Observational studies cannot prove, however, that the diet is the cause.

Why might the gut be affected? Several mechanisms work together. First, fibre is missing, the food of the butyrate producers. Second, emulsifiers can disturb the mucus layer: in a controlled study with carboxymethylcellulose, diversity fell and fewer short-chain fatty acids were produced, and in a small study with the emulsifier E466, bacteria moved closer to the gut wall in two of seven participants. Whether this triggers inflammation in humans is open; the effect depends on the substance and probably on the person. Third, such products often supply plenty of sugar, salt and fat in an easy-to-eat form, which raises eating speed and amount. The chapter on the mucus layer and additives deepens the second point, the sweetener chapter another.

Two final caveats. First, the link runs both ways: people with gut inflammation often eat differently, avoid vegetables and reach for soft, processed food, which makes cause and effect hard to separate. Second, diet is only one lever among several. Smoking, lack of sleep, lack of exercise, overweight, antibiotics and predisposition all contribute, and in inflammatory bowel diseases (Crohn’s disease, ulcerative colitis) genes and the immune system are decisive. A healthy diet helps in these diseases as an accompaniment but does not replace treatment.

Highly processed food with emulsifiers and little fibre can promote inflammation.

Where it comes from and where it leads

The same symptoms can have different roots. This map shows what may be involved in this problem and what may follow from it.

Connections, not certainty: a link means “can”, not “must”. What applies to you is best clarified in a talk with your doctor.

What often helps

Lifestyle

Diet, exercise, sleep, social contact and dealing with stress.

Mediterranean diet as a basis Vegetables, legumes, olive oil, nuts, fish and whole grains. Well studied and practical for everyday life. It is not about a country or a list but about the pattern: mostly plant-based, little sugar, red and processed meat rarely. Promising How we rate the evidence Established Recommended in medical guidelines or supported by several consistent meta-analyses of randomised human studies. Well supported Several randomised studies in humans with largely consistent results. Promising Single randomised or controlled studies in humans, not yet independently confirmed — or many consistent observational studies. Plausible Two cases: first observational or pilot studies with small samples — or a settled basis that is not in dispute, such as movement, sleep or meal pauses. But not tested in humans for symptoms. Experimental Barely studied in humans. Mainly lab and animal studies or theoretical reasoning; whether it helps is open. [1]
Fewer highly processed foods Cook for yourself where you can. Long ingredient lists with additives are a sign of highly processed products. A practical start: replace sugary drinks and snacks, not everything at once. It does not have to be perfect; what counts is what is on the plate most of the time. Plausible How we rate the evidence Established Recommended in medical guidelines or supported by several consistent meta-analyses of randomised human studies. Well supported Several randomised studies in humans with largely consistent results. Promising Single randomised or controlled studies in humans, not yet independently confirmed — or many consistent observational studies. Plausible Two cases: first observational or pilot studies with small samples — or a settled basis that is not in dispute, such as movement, sleep or meal pauses. But not tested in humans for symptoms. Experimental Barely studied in humans. Mainly lab and animal studies or theoretical reasoning; whether it helps is open. [2]
Plant variety, not just amount Eat not only more but more varied: different vegetables, legumes, nuts, herbs and whole-grain types. Each plant feeds different bacteria. Increase slowly so the gut can adapt, otherwise you will bloat. Promising How we rate the evidence Established Recommended in medical guidelines or supported by several consistent meta-analyses of randomised human studies. Well supported Several randomised studies in humans with largely consistent results. Promising Single randomised or controlled studies in humans, not yet independently confirmed — or many consistent observational studies. Plausible Two cases: first observational or pilot studies with small samples — or a settled basis that is not in dispute, such as movement, sleep or meal pauses. But not tested in humans for symptoms. Experimental Barely studied in humans. Mainly lab and animal studies or theoretical reasoning; whether it helps is open. [1]
Sugary drinks first Soft drinks, iced tea and energy drinks were among the foods with the clearest link in the large cohort study. Water, unsweetened tea or coffee are the easiest swap. Promising How we rate the evidence Established Recommended in medical guidelines or supported by several consistent meta-analyses of randomised human studies. Well supported Several randomised studies in humans with largely consistent results. Promising Single randomised or controlled studies in humans, not yet independently confirmed — or many consistent observational studies. Plausible Two cases: first observational or pilot studies with small samples — or a settled basis that is not in dispute, such as movement, sleep or meal pauses. But not tested in humans for symptoms. Experimental Barely studied in humans. Mainly lab and animal studies or theoretical reasoning; whether it helps is open. [3]

Natural supplements

Supplements do not replace a medical check-up. Discuss dosage and interactions with your doctor or pharmacist.

Omega-3 fatty acids Oily fish twice a week is the easiest way. Supplements only after consultation, especially if you take blood thinners. If you do not eat fish, algae oil is an alternative; whether capsules lower inflammation in the gut is not well established for gut diseases. Plausible How we rate the evidence Established Recommended in medical guidelines or supported by several consistent meta-analyses of randomised human studies. Well supported Several randomised studies in humans with largely consistent results. Promising Single randomised or controlled studies in humans, not yet independently confirmed — or many consistent observational studies. Plausible Two cases: first observational or pilot studies with small samples — or a settled basis that is not in dispute, such as movement, sleep or meal pauses. But not tested in humans for symptoms. Experimental Barely studied in humans. Mainly lab and animal studies or theoretical reasoning; whether it helps is open.

Medical treatments

Information, not a treatment recommendation. Decide together with a doctor. Approval and availability differ from country to country.

Get checked if an autoimmune disease is suspected Persistent joint pain, skin rashes or diarrhoea with blood should be examined by a doctor. Established How we rate the evidence Established Recommended in medical guidelines or supported by several consistent meta-analyses of randomised human studies. Well supported Several randomised studies in humans with largely consistent results. Promising Single randomised or controlled studies in humans, not yet independently confirmed — or many consistent observational studies. Plausible Two cases: first observational or pilot studies with small samples — or a settled basis that is not in dispute, such as movement, sleep or meal pauses. But not tested in humans for symptoms. Experimental Barely studied in humans. Mainly lab and animal studies or theoretical reasoning; whether it helps is open.
Have gut inflammation measured Whether there is inflammation in the gut is shown not by a feeling but by a stool test for calprotectin, plus blood values such as CRP. If you have persistent diarrhoea, abdominal pain, weight loss or blood in the stool, have it checked before experimenting with diets on your own. Well supported How we rate the evidence Established Recommended in medical guidelines or supported by several consistent meta-analyses of randomised human studies. Well supported Several randomised studies in humans with largely consistent results. Promising Single randomised or controlled studies in humans, not yet independently confirmed — or many consistent observational studies. Plausible Two cases: first observational or pilot studies with small samples — or a settled basis that is not in dispute, such as movement, sleep or meal pauses. But not tested in humans for symptoms. Experimental Barely studied in humans. Mainly lab and animal studies or theoretical reasoning; whether it helps is open.
With inflammatory bowel disease, get nutrition support With a diagnosed disease such as Crohn’s disease or ulcerative colitis, diet is part of treatment, but not instead of medication. A dietitian experienced with these diseases helps avoid deficiencies and handle flare phases properly. Well supported How we rate the evidence Established Recommended in medical guidelines or supported by several consistent meta-analyses of randomised human studies. Well supported Several randomised studies in humans with largely consistent results. Promising Single randomised or controlled studies in humans, not yet independently confirmed — or many consistent observational studies. Plausible Two cases: first observational or pilot studies with small samples — or a settled basis that is not in dispute, such as movement, sleep or meal pauses. But not tested in humans for symptoms. Experimental Barely studied in humans. Mainly lab and animal studies or theoretical reasoning; whether it helps is open.

In the mood for something completely different? Another one, at random

How we rate the evidence

Trust score 5 of 5:Established: Recommended in medical guidelines or supported by several consistent meta-analyses of randomised human studies.
Trust score 4 of 5:Well supported: Several randomised studies in humans with largely consistent results.
Trust score 3 of 5:Promising: Single randomised or controlled studies in humans, not yet independently confirmed — or many consistent observational studies.
Trust score 2 of 5:Plausible: Two cases: first observational or pilot studies with small samples — or a settled basis that is not in dispute, such as movement, sleep or meal pauses. But not tested in humans for symptoms.
Trust score 1 of 5:Experimental: Barely studied in humans. Mainly lab and animal studies or theoretical reasoning; whether it helps is open.

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