Two studies explain why dietary fibre is so precious for your health
A diet rich in fibers – like those provided by fruit, vegetables and whole meal cereals – reduces the risk of diabetes, heart disease and arthritis, (1) and more in general premature deaths. As shown in a meta-analysis published in 2015 on the American Journal of Epidemiology.
If the value of consuming fibre – at least 25 grams per day, according to EFSA – is well known, less-known is the mechanism that makes it beneficial to health. On the matter two studies were published on Cell Host and Microbe. A study comes by the University of Gothenburg, in Sweden, the other from a team led by Andrew T. Gewirtz, at the Georgia State University.
The virtuous cycle set off by dietary fibre
Dietary fibre do not act directly on your system, the two studies explain, but feeds millions of active bacteria in the intestine. The spoils of the meal are from these released in the form of short-chained acid fats which feed in their turn intestinal cells, which produce more mucus –insulation necessary to protect the intestinal walls from an attack of pathogenic bacteria – and emit anti-bacterial molecules.
Therefore, if fibre is missing in our diet, the bacteria population (microbiota) – which is the protective mucus that protect us from pathogenic bacteria – will narrow, and the immune system will be alerted. The alert activates an inflammation process that can perpetuate and extend from the intestine to the entire system.
The effect of fibre on guinea pigs
The two researches have experimented on lab rats the effects of diets with and without fibre (administered with the integration of inulin). In the guinea pigs used by US researchers, a diet rich in fat and poor in fibre has reduced by 10 times the intestinal bacteria population. In the ones followed by the Swedish team, shifting from a diet rich in fibre to a poor one overturned the microbiota of the lab rats. Many common bacterial species have become rare and the rare ones have become common.
Besides changes to the microbiota, both teams have noticed rapid changes in the lab rats. The lack of dietary fibre has determined a thinning of the layer of intestinal mucus. As a consequence, bacteria has gotten too close to the intestinal walls, thus triggering an immune response which becomes chronic in a matter of days. After a few weeks, the rats started to accumulate fat and develop high-levels of sugar in their blood.
(1) A high consumption of fruit (berries in particular), yellow vegetables, leafy green vegetables and greens (cauliflowers, kale, cabbage, broccoli, Brussels sprouts and other types of cabbages)or their fibers are associated with a low risk of developing type 2 diabetes, has concluded the meta-analysis published in June, 2015 on the Journal of Diabetes Investigation.
Always in 2015, a meta-analysis published on Clinical Nutrition has shown how the consumption of fibers is inversely associated to the risk for coronary disease, especially fibers from cereals and fruit. Moreover, soluble fibre and insoluble have a similar effect. A significant relation dose-response is observed between the intake of fibers and the risk of coronary disease.
Another study published in 2017 on Rheumatic Disease has instead pointed out how the elevated consumption of fibre may be useful both to reducing body-weight (see recent study on The American Journal of Clinical Nutrition) and inflammation, but also helping the treatment of osteoarthritis of the knee.