This newsletter covers the microbiome in depth once a year. The excellent article highlighted herein is comprehensive, and a great resource for those who wish a primer on this pivotal subject. Hugo Rodier, MD
Gut microbiome influences food allergy risks
Healio Minute, February 28, 2024
The gut microbiome has gained attention for its critical role in health and disease in recent years. Among its various influences, the microbiome’s impact on the development and severity of food allergies is particularly important. Approximately 70% to 80% of the body’s immune cells are in the gut. This significant concentration underscores the critical role the gut plays in the immune system, influencing not only digestive health but overall immunity and disease resistance.
Gut-associated lymphoid tissue is a key component of the mucosal immune system and serves as the first line of defense against pathogens that are ingested with food or that come in contact with mucosal surfaces. The gut microbiome is composed of trillions of microorganisms, including bacteria, viruses, fungi and protozoa. It plays a pivotal role in digestion, nutrient absorption and immune system modulation, which is particularly relevant to food allergies. Food sensitivities and intolerances are commonly associated with microbial imbalances. However, the increasing prevalence of food allergies has prompted investigations into environmental and lifestyle factors that may disrupt the gut microbiome, leading to immune dysregulation.
Gut dysbiosis
Dysbiosis refers to an imbalance in the gut microbiome where harmful microorganisms outnumber beneficial ones. This imbalance can alter immune tolerance to food antigens. A diverse, balanced microbiome educates the immune system to distinguish between harmful pathogens and benign molecules, including food proteins. In contrast, dysbiosis can lead to heightened immune sensitivity and the development of allergic responses. Studies have shown that infants with reduced gut microbial diversity have an increased risk for developing food allergies. Early exposure to microbial diversity and the restoration of microbial balance is emerging as a potential therapeutic strategy.
Leaky gut syndrome, characterized by increased intestinal permeability, allows undigested food particles, bacteria and toxins to “leak” through the intestinal walls into the bloodstream. A variety of factors can influence the breakdown of the intestinal lining.
Dietary choices play a significant role. High intake of processed foods, sugar and saturated fats can harm beneficial gut bacteria and promote harmful ones. Low fiber intake reduces the nourishment available for healthy microbes that maintain the integrity of the gut lining.
Overuse of antibiotics is another culprit, as these medications can indiscriminately kill off both harmful and beneficial bacteria, disrupting microbial balance. Any time a patient is put on a course of antibiotics, it is crucial to simultaneously take a probiotic.
Chronic stress also impacts gut health by altering gut bacteria. It can increase intestinal permeability through stress-induced changes in the gut barrier function as well.
Environmental toxins, such as pesticides, pollutants and BPA, further contribute to dysbiosis and can damage the gut lining. Lifestyle factors, including excessive alcohol consumption and lack of physical activity, can exacerbate these effects, leading to an increased risk for gut dysbiosis.
Together, these elements create a complex interplay that can significantly impact gut health. This can provoke an immune response, leading to inflammation and, potentially, to the development of food allergies. Recognizing and addressing leaky gut syndrome in patients presenting with food allergies can be a crucial step in both diagnosis and treatment.
Short-chain fatty acids
In research, significant focus has been placed on the role of short-chain fatty acids (SCFAs) — such as butyrate, propionate and acetate — in modulating the immune system, as they are primary products of gut microbiota digestion. Specifically, butyrate has been shown to boost vitamin A metabolism, which in turn boosts some helpful immune cells and the production of a protective antibody IgA.
SCFAs help by reducing pro-inflammatory cytokines (IL-1B, IL-6, IL-17) while increasing anti-inflammatory mediators (IL-10), positioning SCFAs as crucial in enhancing immunological tolerance to nonharmful antigens and mitigating inflammation. To boost the production of SCFAs, a diet rich in dietary fibers, resistant starches, prebiotics, polyphenols and fermented foods is key. Dietary fibers, abundant in fruits, vegetables, whole grains and legumes, play a pivotal role in this process.
Dietary fibers are not broken down in the upper parts of the digestive system. Instead, they reach the colon, where they become food for the gut microbiota, leading to the fermentation process that produces SCFAs. Resistant starches, found in such foods as cooked and cooled potatoes, green bananas and whole grains, also resist small intestine digestion and undergo fermentation in the colon, contributing to SCFA production.
Prebiotics, which are specific types of fibers that selectively nourish beneficial bacteria, further enhance this fermentation process. Foods such as garlic, onions and asparagus are rich in prebiotics, including inulin and fructooligosaccharides, promoting the growth of SCFA-producing bacteria. Additionally, polyphenols, present in fruits, vegetables, tea, coffee and red wine, can modulate the gut microbiota in favor of these beneficial bacteria. While fermented foods themselves do not directly produce SCFAs, they introduce beneficial bacteria that can participate in fiber fermentation and SCFA production.
By focusing on these dietary components, one can effectively support the gut microbiome’s ability to produce SCFAs, which are crucial for maintaining gut health, reducing inflammation and improving overall well-being.
Gut flora
Recent clinical research, particularly in infants and children, has highlighted the significant role of gut flora alterations in the development of food allergies, where a decrease in Lactobacilli and an increase in Staphylococcus aureus have been linked to allergies to foods such as eggs and milk.
Moreover, S. aureus has been identified as exacerbating allergic conditions such as asthma and atopic dermatitis. Studies reveal that lower levels of beneficial bacteria — such as Lactobacillus and Bifidobacterium — in young infants may raise their risk for developing allergies to egg white, cow’s milk and airborne allergens. However, oral supplementation with specific probiotic strains, such as Ligilactobacillus salivarius and Bifidobacterium bifidum, has been shown to effectively reduce the risk for atopic sensitization to common allergens.
This suggests that probiotics hold therapeutic promise for not only mitigating food allergies but also potentially for food intolerances such as those to gluten and fermentable oligosaccharides, disaccharides, monosaccharides and polyols, or FODMAPs, by promoting beneficial changes in gut microbial diversity.
Preclinical trials support this, showing that probiotics such as Bifidobacterium infantis can correct immune imbalances and reduce allergic symptoms, indicating a preventive approach against food allergies through gut microbiota modulation.
Additional research has highlighted the therapeutic potential of probiotics and prebiotics in managing food allergies, specifically milk allergies. Synbiotic formulations, which combine probiotics or prebiotics with dietary components, have shown promise in reducing allergy symptoms in mice studies.
These mixtures, particularly when combining probiotics with oligosaccharides, can lessen allergic reactions and modify gut microbiota by lowering mast cell numbers and reducing swelling. Clinical trials have begun to explore the efficacy of probiotics and prebiotics in preventing or reducing the severity of other food allergies. While results are promising, further research is needed to identify specific strains and dosages that are most effective.
Clinical practice
Grasping the link between the gut and allergies is key in identifying and managing food allergies effectively. When taking a patient’s history, it is important to ask about gut health and any symptoms that might indicate an imbalance. Direct signs include digestive issues (diarrhea, gas, bloating) and sometimes a feeling of being uncomfortably full. Physicians should also be on the lookout for indications of poor nutrient absorption, which could point to a leaky gut.
Unexpected food sensitivities or the sudden appearance of food allergies could signal issues, as the leaked substances might spark off-target immune responses. Acne or eczema, mood swings, unexplained fatigue or signs of autoimmune diseases such as rheumatoid arthritis might also suggest a leaky gut. Such diverse symptoms underscore the complex ways gut health can influence overall well-being, highlighting the need for a comprehensive approach in patient care.
As research continues, the role of doctors in diagnosing, educating and treating patients with food allergies becomes increasingly important. Stool tests that analyze microbial balance can be a helpful tool. Educating patients about the role of gut health in allergies is equally important. Dietary modifications to support a healthy microbiome, the judicious use of antibiotics and potentially the use of probiotics and prebiotics should be discussed as part of a holistic approach to allergy management. Physicians can offer patients comprehensive care that addresses the root causes of allergic reactions, paving the way for more effective treatments and improved patient outcomes.
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