Diet, microbiome and vaccine side effects: overview
- Study links gut microbiome differences to Covid-19 vaccine fever
- Higher flagellin expression was associated with stronger fever symptoms
- Diets high in fat and additives correlated with inflammation
- Vegetarian diets were linked to microbiome features linked to less fever
- Findings may support dietary strategies without affecting antibody responses
The microbiome is highly influential on many aspects of human health, from digestion and immunity to cognition and metabolism.
A new study published in the journal Science suggests that its influence could also extend to how people react to vaccines.
This is, in turn, linked to diet, which is highly influential on the microbiome. Changing one’s diet, the research suggests, could influence how one reacts to a vaccine.
Vaccine side effects and the microbiome
People vary widely in how they react to vaccines. Fever and flu-like symptoms are among the most common side effects, but not everyone experiences them. Such side effects often discourage people from taking vaccines.
This variation in symptoms, according to the study, is not well understood. However, the researchers speculated that the gut microbiome, which influences immune activity, could play a role.
In order to test their hypothesis, the researchers profiled the faecal microbiomes of 171 young adults before and after receiving the mRNA vaccination for SARS-CoV-2 (the virus that causes Covid-19). Temperatures were taken three times a day to quantify fever.
The study found that some gut bacteria, such as Lachnospiraceae, produce flagellin, a protein that can activate inflammatory immune pathways and intensify reactions to the vaccine.
Those with greater intestinal inflammation prior to taking the vaccine, or greater flagellin expression (meaning genes were activated to produce flagellin) in the gut, were more likely to develop fever after taking it.
Furthermore, there was a strong correlation with particular diets and vaccine side effects.
How diet could influence vaccine side effects
The researchers found that diets consisting of greater levels of fat or processed food additives, or lower in whole plant foods, tended to be correlated with the inflammatory microbiome that was linked to fever.
At the same time, vegetarian diets were correlated with features linked to less fever.
Importantly, the researchers found that inflammation and diet do not affect how antibodies react to vaccines, meaning that diet does not appear, in this context at least, to affect how vaccines impact immunity itself.
What could this mean for industry?
Dietary modification may be a viable strategy to reduce vaccine-related side effects in the future, according to the study.
“Diet, microbial ecology, and the metabolic state are not immutable, and people might one day prepare for vaccination as deliberately as the vaccine itself is formulated,” writes Bali Pulendran, an immunologist from Stanford University in a perspective reacting to the study.
The backlash against ultra-processed foods has already significantly shaped the food industry, with demand for clean label food being one of the driving forces behind product development. Additives, often associated with ultra-processed food, were correlated in the study with the inflammatory microbiome that was in turn associated with fever.
Causality must still be established by future studies. Yet the suggestion that diets containing additives could heighten vaccine side effects could be yet another win for clean label food.
The significant role of vaccine side effects in hesitancy suggests that they are a concern for many people. If they could be mitigated through diet, this could prove yet another driver for the popularity of the clean label movement, and on the flip-side, further entrench distrust of ultra-processed food.
