Two new Australian studies suggest that a diet rich in fiber could help to reduce allergies to foods such as peanuts.
In one study, which is also one of the first to look specifically at fiber deficiency in the gut, Laurence Macia and Charles Mackay, both immunologists at Monash University in Australia, bred a group of mice to have artificially-induced peanut allergy, and then fed them a high-fiber diet to produce a healthy population of gut bacteria.
This healthy bacteria was then given to a group of mice that had no gut microbes of their own. Although this group of mice had not been fed a high-fiber diet, they still benefited from the bacteria from the mice who had, and showed a less severe allergic response.
It appeared that the fiber actually changed the gut and colon microbiota — the bacteria in the gut — which then had a protective effect against the allergy.
The fiber is beneficial for the gut microbiota as the bacteria break it down into a byproduct called short-chain fatty acids. These acids have a protective effect on the immune system and help regulate inflammation in the gut, which can flare up during an allergic reaction to food.
This protective effect was even seen when the mice were fed an artificial administration of these fatty acid byproducts rather than the high-fiber diet itself, with the mice showing a reduced allergic response after just three weeks of receiving the fatty acids.
Another study from the university, this time led by Jian Tan, which also found that mice allergic to peanuts were protected against the allergy when fed a high-fiber diet also pointed to vitamin A playing an important role in reducing and preventing allergies.
Vitamin A is needed by part of the immune system called dendritic cells, which control whether an allergic response against a food allergen happens or not.
An increased level of short-chain fatty acids from the breakdown of fiber can switch these cells to stop the allergic response, whereas a lack of fiber can have the opposite effect and switch on the allergic response.
As vitamin A is required by these dendritic cells to function it is another important factor in helping to protect against allergies and to help switch off the allergic response.
Vitamin A can only be obtained from food and is found in high quantities in vegetables and fruits (which are also high in fiber) and in particular in yellow, red and green (leafy) vegetables, such as spinach, carrots, sweet potatoes and red peppers, yellow fruit such as mango, papaya and apricots. It is also found in cheese, eggs, oily fish, kidney, liver, milk and yogurt. Although a deficiency in adults is unusual, it could help explain some high levels of allergies that occur in children.
However both teams recognize that more research needs to be done and are now planning to conduct further studies.
The findings were published online in the journal Cell Reports.