Just as you're finishing a clinic visit with a patient, "Hey doc, I have a quick question: why are there so many more allergies now than in the past?"

I don't think I could count how many times this exact scenario has played out in my office. The answer I generally give revolves around "a complex interaction between genetics, the environment, and factors we don't really understand."

This answer may be evolving and changing as new science sheds more light on the development of the immune system regarding allergies. The 2024 American Academy of Allergy, Asthma, and Immunology Annual Meeting had a number of sessions that discussed the microbiota within the context of allergic disease development and treatment. There's been so much discussion of the microbiota in all specialties that I can see, and quite remarkably, a lot of it seems very reasonable and insightful.

Evidence shows a profound loss of gut microbial diversity as society has shifted from traditional to industrial lifestyles. Industrialization seems to be a key factor in driving the increase in allergic disease. Sampling the gut microbiome of newborn infants as they develop and comparing them to people in traditional farming communities that are not industrially developed, investigators are finding remarkable differences. Not only are there different species of bacteria present in the gut in these different lifestyles and environments, but there are also alterations in intestinal peptides that may exhibit properties ranging from antimicrobial to pro-inflammatory. This supports the theory of the hygiene hypothesis and helps to underpin the science.

Additionally, there's evidence that bacterial diversity in the home can influence individuals' gut microbial composition. Homes with dogs tend to have greater microbial diversity than those with cats or no animals at all. Thus, the combination of microbial depletion or the functional loss of the organisms that regulate immune pathways to protect against allergic disease could be variables driving this increase. Furthermore, pharmaceutical interventions to the gut microbiota, either with supplementation or bacterial extracts or even antibiotics, have the potential to shape our gut health and ultimately impact allergic and immunologic diseases.

Susan Lynch, PhD, an expert in gut and airway microbiomes, discussed the evolving gut microbiome in the context of industrialization. Dr. Fernando Martinez, an expert in pediatric respiratory disease, reported on novel treatments with bacterial extracts composed of Staphylococcus, Streptococcus, Klebsiella, B. catarrhalis, H. influenzae, and M. catarrhalis. This was given orally to young kids and seemed to reduce the severity of lower respiratory illnesses, reducing the chance of wheezing attacks. Dr. Rima Rashid, an expert in food allergy, discussed her work in fecal microbiota transplantation (FMT) for food allergy. Remarkably, this treatment, when given to peanut-allergic children, increased their threshold of reactivity to peanut in an oral challenge. So, yes, eating poop helped food allergies! Forty percent of children increased their threshold of response from 100 mg of peanut protein or less to 300 mg or 600 mg of protein — which is the equivalent of up to three peanuts.

So certainly, the concept of a probiotic as beneficial for daily health has evolved past that to a deep detailed science which may help further explain the rise of allergic disease, asthma, and especially food allergy. And someday also lead to novel treatments.

Dr. Singla has no conflicts of interest to report.

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