Prebiotics beyond inulin: HMOs, arabinogalactan, polyphenols

Healthy state

Besides inulin and fructo-oligosaccharides, there are substances that feed specific bacteria. Three are particularly interesting: human milk oligosaccharides (HMOs), arabinogalactan and polyphenols. A prebiotic Prebiotics Food components, usually certain fibres, that specifically feed beneficial gut bacteria, such as inulin or GOS. More in the chapter “Prebiotics that build up gently” is a substance that certain gut microbes use and that benefits health as a result. The second part matters: that a bacterial group grows is only an intermediate result, not yet a benefit to you.

HMOs are sugar chains from breast milk. The infant can barely digest them itself. They are meant for the bacteria, above all bifidobacteria, which have special enzymes for them. In the lab some HMOs also act as decoys: pathogens attach to them instead of the gut wall. Individual HMOs are now manufactured, such as 2'-fucosyllactose (2'-FL) and lacto-N-neotetraose (LNnT). In 100 healthy adults they increased bifidobacteria, and up to 20 g a day was well tolerated.

Arabinogalactan is a highly branched fibre, usually from larch wood. In a study with 30 adults (15 g a day for six weeks), Bacteroidetes increased and bifidobacteria tended to as well. Branched fatty acids such as isovaleric acid, which come from protein fermentation, fell. Symptoms did not increase.

Why bifidobacteria in particular are a target: they mainly make acetic acid (acetate) and lactic acid (lactate). Other bacteria in the colon take up these substances and turn them into butyrate 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”, the most important fuel of colon cells. This is called cross-feeding, feeding indirectly. But it only works if the right butyrate producers are present. In people who lack them, it stops at acetate and lactate.

Polyphenols are plant pigments and bitter compounds, for example from berries, cocoa, green tea, coffee, pomegranate and walnuts. Only a small part is absorbed in the small intestine; the larger rest reaches the colon, often bound to plant fibres. There, bacteria break them down and change in the process: some polyphenols slow certain germs, others serve as food. A meta-analysis Meta-analysis An analysis that combines the results of several studies. It is only as good as the studies it includes. of 50 randomised trials Randomised trial A study in which chance decides who gets the treatment and who does not, for comparison. This makes results particularly reliable. with over 2000 adults found more bifidobacteria in 82 % of studies, more Akkermansia Akkermansia A gut bacterium that lives on the mucus of the gut wall and stimulates its renewal. In studies, high levels often go along with good metabolic health. More in the chapter “The mucus layer and additives” in half, and more butyrate overall.

Which polyphenols are best researched: flavonoids, meaning flavanols from cocoa and green tea and anthocyanins from berries, increased bifidobacteria and butyrate most clearly and consistently. Phenolic acids, for example from coffee and whole grains, mainly affected Akkermansia. Individual studies: a flavanol-rich cocoa drink increased bifidobacteria and lactobacilli, a wild blueberry drink increased bifidobacteria. A polyphenol-rich diet lowered a blood value measured as zonulin in older people. Such zonulin tests are considered unreliable, however, so this says little about the gut barrier.

Disrupted state: causes and effects

Not everyone benefits equally. From ellagitannins (pomegranate, walnuts, strawberries) some people make a lot of urolithin, others hardly any, depending on whether the right bacteria such as Gordonibacter are present. Researchers call these metabotypes. The same applies to other plant compounds: whether Akkermansia responds to polyphenols also depends strongly on the existing gut flora 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”. Someone with little diversity after many antibiotics may use the same diet differently from someone with a rich flora.

HMOs in IBS Irritable bowel syndrome Recurring abdominal pain linked to bowel movements, without tests finding another cause. Today it is understood as a disorder of gut–brain interaction. More in the chapter “The gut-brain axis”: in the controlled trial with 60 patients, 10 g a day increased bifidobacteria, but symptoms followed the same course as with placebo Placebo A dummy treatment without an active ingredient. Comparing with it shows how much a remedy achieves beyond expectation and chance. . Four weeks after stopping, the effect was gone. The often-quoted improvement comes from a large study without a control group. In mild ulcerative colitis, 2'-FL showed no clear effect on disease signs in a small controlled trial.

More bifidobacteria are not a goal in themselves. Bifidobacteria are generally welcome, but a healthy gut lives on the mix of many groups. A single fibre promotes individual groups but does not replace a varied diet. Arabinogalactan even slightly reduced species diversity in the study. And if your gut is sensitive, you notice changes faster: GOS, another substance in this group, counts as a FODMAP FODMAP Short for fermentable sugars and sugar alcohols that are poorly absorbed in the small intestine, such as fructans, lactose, fructose and sorbitol. More in the chapter “Doing low-FODMAP right” and can cause bloating. How quickly fibres are fermented and why that matters for tolerance is covered in the chapter on gently building prebiotics.

More is not better: high-dose extracts act differently from food. The European Food Safety Authority EFSA could not set a safe daily amount for EGCG from green tea extracts; in studies, liver values rose from about 800 mg a day. A cup of tea provides far less; regular tea drinkers get 90 to 300 mg a day. A food brings water, fibre and many compounds together; the powder brings only one.

Two side effects that are often overlooked. Tannins in tea, coffee and cocoa bind iron from plant foods and lower its uptake when drunk with meals. This matters above all in iron deficiency, in pregnancy and in women with heavy periods. And in histamine Histamine A messenger substance of the body that is also found in aged and fermented foods. Too much can cause headache, flushing or diarrhoea. More in the chapter “Histamine intolerance: much searched, little proven” intolerance, cocoa and some teas appear on many lists as possible triggers. How well this is supported is unclear; the chapter on histamine has more.