When the supplement itself is the problem: iron, magnesium, excipients and more

Healthy state

Supplements are meant to fill a gap, for example in iron deficiency, low vitamin D or too little fibre. For the body to use a substance, it has to absorb it in the small intestine. Whatever is not absorbed there moves on into the large intestine. There it can bind water, be fermented by bacteria or irritate the lining.

For many minerals, absorption is limited. The body absorbs iron and magnesium only in small portions and regulates this itself according to need. For iron there is a dedicated hormone, hepcidin: if there is enough, or a large portion has just arrived, hepcidin rises and slows absorption for about a day. That makes sense, because too much iron is harmful. But it also means that a large part of a high dose passes through the gut unchanged.

A tablet is also never just the active ingredient. So that it can be pressed, keeps, tastes good and dissolves at the right moment, excipients are added: fillers, binders, coatings, sweeteners, dyes. For medicines they are usually listed in the package leaflet, for supplements on the packaging. For most people these amounts are unproblematic.

Disrupted state: causes and effects

Iron tablets are among the most common triggers. 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 43 studies with almost 7,000 adults found that ferrous sulfate, the usual form, more than doubled gastrointestinal complaints such as nausea, constipation, diarrhoea and abdominal pain compared with placebo Placebo A dummy treatment without an active ingredient. Comparing with it shows how much a remedy achieves beyond expectation and chance. . The unabsorbed iron in the colon also acts on the bacteria: many pathogens need iron to grow. In a study with infants in Kenya, iron-fortified porridge increased enterobacteria and disease-causing E. coli strains, and an inflammation marker in the stool rose. For adults in Europe the situation is different, but the mechanism is the same.

Magnesium draws water into the gut. What is not absorbed in the small intestine holds water in the colon and softens the stool. Magnesium oxide is therefore used as a laxative: in a study with 90 people with constipation, it improved symptoms just as well as senna. Anyone taking magnesium for cramps or for sleep gets this effect unintentionally. The EU food safety authority sets an upper limit of 250 mg a day for magnesium from supplements, not counting magnesium from food.

Excipients are often overlooked. An analysis of more than 42,000 medicines counted an average of 8.8 excipients per tablet or capsule. 45 percent contained lactose and 55 percent at least one fermentable sugar from the 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” group, such as mannitol or sorbitol. These are usually small amounts. But anyone who takes several tablets a day, reacts sensitively to FODMAPs or sucks chewable tablets and gummy vitamins with sugar alcohols Sugar alcohols (polyols) Sweeteners such as sorbitol, xylitol or maltitol, which also occur in fruit. They are barely absorbed and can cause bloating and diarrhoea. More in the chapter “Lactose, fructose, gluten: making sense of intolerances” quickly reaches a noticeable amount.

Protein powders, bars and sports drinks are a separate source of trouble. Whey protein concentrate contains lactose, and many powders contain sweeteners, sugar alcohols, inulin or thickeners. Creatine can cause diarrhoea in larger single servings: among 59 footballers, 56 percent got diarrhoea with 10 grams at once, while with two doses of 5 grams it was no more common than with placebo.

Even things meant to help the gut can burden it. Fibre supplements such as inulin ferment strongly and cause bloating in a sensitive gut. Not everyone tolerates probiotics Probiotics Live microorganisms that are meant to provide a benefit in sufficient amounts. The effect depends on the individual strain. More in the chapter “Using fermented foods well”: in a small study of people with brain fog and bloating, all those affected had been taking probiotics, and after stopping them together with antibiotic treatment, symptoms improved in most. How much of that was due to stopping cannot be separated in the study.

The tricky part is that symptoms often come gradually and nobody thinks of the product. Anyone who starts several products at once can no longer tell which one is causing trouble. And because many products are taken because of gut symptoms, a cycle easily develops: the symptoms get worse, so the next product is added.