Immune boosting foods and your microbiome

The concept of immune boosting foods generally centers around the theory that increased levels of everyday nutrients involved in immunity will boost it. A great example is the use of high dose vitamin C for the prevention of the common cold.

But human physiology is vastly more complicated than that. Furthermore, “Immune boosting foods” is sort of a misnomer. It implies that simply eating a food when you think you’re going to get sick is adequate protection. It’s not.

Generally speaking, behaviors and nutrition build a strong and robust immune system through increasing resilience. These behaviors don’t just become important when a virus makes its way through the population. You practice them long-term, and as a result, they build resilience throughout the body.

The results of a new paper shine a spotlight on this notion, and not surprisingly, the microbiome is involved.

The microbiome boosts viral immunity

The micobiome is a hot area of research in immunology. This makes sense, research identifies the microbiome as a major player in the development and training of the immune system. In return, the immune system shapes the microbiome.

A new paper published this week identifies how this works. This, coupled with other data gives us a glimpse in to how global dietary patterns benefit the microbiome, and thus, viral immunity.

Bacteroides are a common genus of bacteria in the human microbiome. Certain members of the Bacteroides genus contain a special glycolipid in their outer membrane. When our immune system recognizes this, it secretes interferon-beta(IFN-B).

Interferon-beta is an important part of our immune response to viruses. In this study, stimulation of IFN-B by Bacteroides fragilis increased IFN-B in the gut and throughout the body.

This improved resistance to viral infection and reduced the severity. Multiple members of the genus Bacteroides contain this same component, including most within the B. fragilis group.

In this study, more than 60% of the mice without these microbes caught the virus and less than 50% survived. In mice harboring these microbes, the infection rate was ~15%, and ~95% survived.

Immune boosting foods boost B. fragilis

A study earlier this year found that treatment with nebulised IFN-B improved outcomes and sped up recovery from COVID-19 illness.

Bacteroides also boost immunoglobulin A

Interestingly, immunoglobulin A(IgA) is another important part of the early neutralizing response to SARS-CoV-2 infection. IgA is also necessary for colonization with Bacteroides fragilis, the microbe utilized in the study above.

As it turns out, it seems that members of the B. fragilis group stimulate production of IgA, which allows it to live in the mucus layer of the gut. Consequently, this boosts resistance to viral pathogens.

Immune boosting foods and habits that stimulate Bacteroides abundance

So what can we do to increase the prevalence of B. fragilis in our gut and potentially enhance viral immunity? Soluble fiber intake appears to increase the presence of B. fragilis, stimulating IgA production, and potentially enhancing viral immunity.

Insoluble fiber had no beneficial impact. Foods high in soluble fiber include beans, oats and other grains, brussels sprouts, avocados, and many types of fruit.

Furthermore, Bacteroides follow a strong circadian rhythm, increasing at night and peaking in the early active period. In theory, this should enhance viral immunity by increasing IFN-B and IgA production just prior to our active period, when we’d normally be exposed to viruses.

Therefore, maintaining good circadian habits is also a critical piece of the puzzle in promoting Bacteroides abundance and timing of viral immunity.


Immune boosting foods are a “thing”, but the concept needs updating. Don’t just increase the consumption of citrus fruits when a virus is going around. Focus on building good long-term dietary and behavioral patterns that support your physiology by building resilience.

The microbiome is a crucial piece of the immune boosting puzzle. But long term dietary and behavioral patterns are far more important than short-term changes. Increasing soluble fiber intake and building good circadian habits may provide the boost you’re looking for to reduce the chance of viral infection, and reduce the severity once infection is established.

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