Irritable bowel syndrome (IBS) is the most commonly diagnosed gastroenteric pathology. Several forms have been identified, encompassing a spectrum of symptoms such as constipation, diarrhea, chronic abdominal pain and a regular feeling of discomfort. What these forms have in common is a malfunction of the intestinal muscles, which prevents digestion from proceeding smoothly. Other markers are being investigated to explain the persistence of symptoms, notably chronic inflammation of the intestinal mucosa or loss of intestinal flora diversity.
Given that studies suggest that tea may have a beneficial effect on the enrichment of intestinal flora diversity and on the formation of abnormal intestinal cells, we may well ask whether tea can have an effect on IBS.
So far, the effects of tea or tea extracts have focused on gastrointestinal protection, i.e. the ability of tea polyphenols to protect intestinal tissue from external (pathogens, chronic inflammation) and internal (carcinogenesis, immunity, etc.) aggressions, but only speculations have been made for IBS.
Studies in mice have shown that Maojian green tea extracts are able to reduce constipation-induced IBS by activating motor molecules present in muscle fibres, calmodulin and myosin. This information is interesting because it means that tea would also have direct physiological effects on intestinal muscles. However, when it comes to studies on caffeine-rich foods, the effects on muscle tissue need to be studied, as caffeine can activate them. To date, there are no studies on caffeine in tea and IBS, but it is known that caffeine in coffee increases the severity of IBS.
If we synthesize this scarce information, tea would have a positive action on IBS, at least in the form associated with constipation, but when IBS is well established or attacks occur regularly, caffeine would reinforce IBS.
But what happens when IBS sets in?
In March 2023, a median 12.4-year follow-up of over 423,000 people was carried out to see whether tea and coffee reduced the likelihood of IBS occurrence. For people drinking less than a cup of tea a day, the risk of IBS decreased by 25%, but no longer decreased at more than 4 cups of tea a day, and this was unrelated to lifestyle and physical characteristics.
These variations are quite similar to those for coffee, but for coffee the risk decreases by 25% with more than 4 cups of coffee. Interpretation of this result is tricky, as we don't have the quantities of caffeine and polyphenols in the tea leaves and coffee beans consumed. What's more, another study in overweight and obese people showed that caffeine consumption could increase the severity of IBS symptoms, and another study on LiuBao dark tea suggests a preventive power of dark tea on the onset of IBS.
All these conclusions may be misleading, but they are justified by our current understanding of pathologies. If I take cancers as an example, some will have a well-preserved pathological profile, which makes it easier to predict evolution and treatment. On the other hand, some tumors are very different from one another. For example, one type of tumor may have several subgroups, each with its own calling card (one grows rapidly but spreads less, one has as yet unknown patterns of progression, etc.), and this is what happens with IBS. There is a spectrum of sub-groups that would explain the different effects.
We have seen, for example, that overweight and obese people with IBS could trigger more severe symptoms with caffeine (stronger chronic intestinal inflammation, disturbed motricity, different microbiota).
An IBS sufferer with constipation and potentially poor intestinal motricity could benefit from the beneficial effects of tea and caffeine.
An IBS sufferer with an imbalance of intestinal flora could benefit from the effects of tea polyphenols.
There are no standard answers for tea and irritable bowel syndrome, because each cause and condition would be different from person to person. We need to draw up "calling cards" and understand the biological parameters on which tea acts in these cards, so as to be able to tell the person whether or not tea will amplify the risk of IBS, or attenuate or increase IBS symptoms.
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