In the last decades the prevalence of allergies has increased enormously. Several studies suggest that one of the contributing factors is the reduced intake of fibers in the Western diet. In mice as well as in humans, researchers have found associations between a low fiber intake and the severity of allergic symptoms. Oral supplementation of fibers, also known as prebiotics, could be a promising strategy to prevent or treat allergic diseases.
According to the World Health Organization, a steady increase in the prevalence of allergic diseases globally has occurred, with about 30-40% of the world population now being affected by one or more allergic conditions . This number is still rising: sensitization rates to one or more common allergens among school children are currently approaching 40%-50% . One of the hypotheses for the increase is called the ‘hygiene hypothesis’. This theory proposes that improvements in hygiene led to a reduction in exposure to environmental microbes, which impairs a healthy maturation of the immune system. This could lead to the development of allergic diseases like asthma, rhinitis and atopic eczema.
Coincident with the increase of allergies, there has been a change in the Western diet towards an eating pattern with less fibers and thus less prebiotics. Recently the focus of research has shifted towards the influence of this diet and the gut microbiome as contributors to the increasing prevalence of allergic diseases in Western countries. Several studies have shown that a reduced consumption of whole foods and fibers is associated with worse asthma outcomes . This theory is bolstered by a study which found that children in rural Africa eat twice as much fiber as European children, and allergies are rare .
Prebiotics and short chain fatty acids
Prebiotic fibers are linked to beneficial effects in inflammatory disorders like allergies . These fibers are complex carbohydrates consisting of both soluble and insoluble components and play an important role in the health of the gut microbiome. Many of these fibers are broken down by the gut bacteria into short-chain fatty acids (SCFAs). SCFAs are anti-inflammatory, promote gut homeostasis, strengthen the epithelium, and regulate the size and function of the T-regulatory cells in the immune system . A recent mice-study showed that a high-fiber diet promotes a microbiome that produces high levels of SCFAs, and also that SCFAs protected against allergic airway disease not only in adult mice, but also in their offspring . Another study showed that mice fed on high fiber diets suffered less severe peanut allergies than those that were fed a common diet higher in fat and sugar . The influence of SCFAs is not the only mechanism in promoting health by eating fibers. Other studies found that dietary fibers also have beneficial effects independent of SCFAs, by blocking innate immune receptors and thus suppressing inflammatory reactions [7,8,9].
Relieving asthmatic symptoms by taking supplements
Although the benefits of fiber are well documented, the human consumption of fiber is relatively low. In Europe, adults are recommended to consume between 25-40 grams fibers daily. The actual intake, however, is between 15 and 27 grams per day . Supplements with prebiotics can possibly help prevent or treat allergic symptoms.
A higher intake of fiber has been shown to protect against airway allergic responses[11,12], but there is evidence that in people with severe asthma the consumption of fiber is reduced. This is in turn associated with worse asthmatic symptoms . Although research in humans in this area is not as advanced yet as in mice, several studies in humans found that supplementation with prebiotics can have positive effects on allergic symptoms. Two studies, which investigated the use of oral fiber supplements, showed that lung function improved and gene expression was downregulated in individuals with asthma after using the supplement once  or after a 7-day-use . Although this field of research is still in it’s infancy, the first results are promising. Interventions such as oral supplementation with fiber could beneficially modulate the intestinal microbiota and in turn the severity of asthmatic symptoms. This might be an effective strategy for prevention or treatment of asthma and other allergies.
What are prebiotics?
Prebiotics are fermentable complex carbohydrates and dietary fibers. Prebiotics are not digested in the small intestine, but reach the colon intact, where they ‘feed’ the microbiota. Examples of prebiotics are: fructooligosaccharides (FOS), galactooligosaccharides (GOS), acacia fiber, resistant dextrin, and inulin. They play an important role in both gut health and overall health. Prebiotic dietary fibers are components of fruit & vegetables, whole grains, potatoes, seeds, nuts and legumes. The latest definition of a prebiotic is:
“A prebiotic is a substrate that is selectively utilized by host microorganisms conferring a health benefit.”
This definition was formulated by a panel of experts of the International Scientific Association for Probiotics and Prebiotics in 2016 .
- Pawankar R, Canonica GW, Holgate ST, Lockey RF. World Health Organization. White Book on Allergy 2011-2012 Executive Summary.
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- European Commission, Dietary Fibre. https://ec.europa.eu/jrc/en/health-knowledge-gateway/promotion-prevention/nutrition/fibre
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