Do We Really Need to Boost Our Immunity?

By Emeran Mayer, MD

As the COVID-19 pandemic has engulfed the world, there has never been a time in which topics like Gut Health, Immune Support, Gut Cleansing, and Improvement of Gut Health have been more popular. Suddenly experts from the fields of functional and integrative medicine, nutrition and wellness have all jumped on this new trend. Podcast, master classes, social media posts and advertisements, bestselling books have all driven the frenzy around these topics, while scientific evidence from well controlled human studies have lagged behind.

As a clinician and scientist who has studied the gut, its endocrine, nervous and immune systems, and the brain for the better part of my career, it is remarkable to follow this explosion of information and interest.

In this edition of the Gut Health Insights, I start with one of the main topics of discussion, the Immune System, and will continue in future editions with Gut Cleansing, Leaky Gut, SIBO and Gut Health in general.

The great majority of advice that lay audiences get from books and the experts on social media, implies that we need interventions to boost our immune system, implying that there is a blunted, inadequate, or compromised response of the immune system contributing to many of our chronic health problems, ranging from autoimmune diseases and allergies to colon cancer and Parkinson’s disease, and including the COVID-19 epidemic. However, looking at the science, it becomes quickly apparent, that nothing could be more wrong.

As I explain in great detail in The Gut Immune Connection, a maladaptive increase in the engagement of the immune system in response to diet-induced changes in the gut microbiome does play a crucial role in most of the disorders making up our chronic non-communicable disease (CNCD) epidemic. The exaggerated, inadequately restrained response of the gut associated immune system is not only responsible for the number of autoimmune disorders (including inflammatory bowel disorders and celiac disease), allergies (asthma, food allergies) but also for the CNCDs, all of which have been increasing during the past 75 years.

Even though there are different immune mechanisms underlying these different groups of disorders, they all share one mechanism, which is the compromised ability of the immune system to turn on the breaks once activated. An important factor in these compromised breaking mechanisms is related to an inadequate production of short chain fatty acids by the gut microbiota, and the resulting insufficient activation of a group of immune cells that produce a powerful anti-inflammatory molecule call interleukin 10, or IL-10. This insufficient production of the immune system’s own powerful anti-inflammatory molecule can occur long before we are born or can develop later in life.

Let’s start with what happens during pregnancy. An important component of the maternal influence on the infant’s microbiome and immune system are short chain fatty acids (SCFAs), derived from the fermentation of dietary fiber by intestinal microbes in the mother’s gut. The amounts and types of SCFAs that are produced there and transferred to her baby depend on the maternal microbial ecosystem, which in turn is shaped by her diet. As discussed in detail in The Gut Immune Connection, when pregnant women eat a largely plant-based diet rich in fiber or Microbe Accessible Carbohydrates(MACs), SCFA-producing microbes thrive, and increased amounts of SCFAs, in particular butyrate not only have an anti-inflammatory effect on the mother’s gut and body but are transferred to the developing fetus as well. Recent research suggests that SCFAs not only control inflammation but influence the maturation and reactivity of the fetal immune system. Specifically, they stimulate the development of a population of immune cells (regulatory T cells, or Tregs), which produce anti-inflammatory molecules (in particular the cytokine IL-10) crucial for the prevention of inappropriate immune activation in the gut, leading to autoimmune diseases and allergic reactions.

In the adult, diet-induced short chain fatty acid production exerts an anti-inflammatory effect in the context of a leaky gut, reducing both the inappropriate immune activation in the gut, but also preventing the distal effect of metabolic endotoxemia on other organs.

As explained in a previous article from this newsletter, reduced butyrate and SCFA production, leading to a hyperresponsiveness of the immune system may also play a role in the greater susceptibility and graver outcomes in patients with COVID-19 infections. Individuals with NCNDs are more vulnerable to the infection, and hyperreactivity of the immune system (cytokine storm) has been associated with more severe symptoms. On the other hand, patients on immunosuppressive medications have NOT been found to be more susceptible to the virus.

In summary, our bodies generate their own immune support, as long as we feed our microbes a healthy diet full of fiber and other large molecules which act as prebiotics for our gut microbes. There is no scientific evidence that additional “immune support” or boosting of our immune system in the form of all kind of supplements is needed.


Dr. Emeran Mayer is a Distinguished Research Professor in the Departments of Medicine, Physiology and Psychiatry at the David Geffen School of Medicine at UCLA and the Executive Director of the G. Oppenheimer Center for Neurobiology of Stress and Resilience at UCLA.


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