Got the flu? Eat fiber!

Hey everyone, I recently wrote this article for Science Writers Calgary, which is a writing group based at the University of Calgary. Please check out other articles on their website!

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It’s that time of year again. Flu season is right around the corner, so you better stock up on vitamin C, ginger tea, and…fiber?

That’s right, I said fiber. A new research study published in Immunity has shown that a diet rich in fiber can be protective against influenza infection. So how does this work? 

You get fiber from your diet, and it is important to know that your own body cannot digest fiber so specialized microbes in your gut take on that responsibility. These bacteria are equipped with unique enzymes that can break apart foods with complex carbohydrates such as whole grains, legumes, nuts and seeds into simple sugars like glucose so that your cells are able to absorb the nutrients. 

 

When bacteria break down dietary fiber, they release molecules called short-chain fatty acids as a by-product which get absorbed into the circulation. Short-chain fatty acids have recently gained more attention in the field of inflammation and chronic disease because of their anti-inflammatory properties. In fact, diseases like colitis, arthritis and asthma are improved when you have more short-chain fatty acids present in the body. 

 

If you look at this from another point of view, having an anti-inflammatory environment in the lung may open the door for a pathogen to find its way in and cause infection. The authors of this study asked if this would this be the case for a viral infection in the lung. After feeding mice a high-fiber diet versus a diet with very low amounts of fiber, the authors challenged the mice with influenza virus and measured the inflammatory response in the lungs.

 

Surprisingly, the author’s original hypothesis was wrong, and mice infected with influenza did a lot better after being on a high fiber diet compared to mice that did not eat extra fiber. They showed specifically that butyrate, a short-chain fatty acid produced by bacteria in the gut acted on various immune cells to dampen inflammation in the lung associated with influenza infection. 

 

Now does this make you want to eat more fiber during flu season?

 

Here are a few questions that we still don’t know the answers to:

·     How much fiber do you need to eat to have a protective effect?

·     Are different sources of fiber better than others?

·     Can too much fiber be a bad thing?

·     Does a high fiber diet also protect you from other infections? 

 

Foods that are high in fiber (not an exhaustive list):split peas, lentils, beans, broccoli, raspberries, blackberries, avocados, pears, bran flakes, whole-wheat pasta, oatmeal, flax seeds, chia seeds.

 

Reference:

Aurélien Trompette et al. 2018. Dietary Fiber Confers Protection against Flu by Shaping Ly6c− Patrolling Monocyte Hematopoiesis and CD8+ T Cell Metabolism. Immunity 48 (5): 992-1005; doi: 10.1016/j.immuni.2018.04.022