Modern food habits have led to a decline in the number of beneficial microorganisms humans get from diet
Together, food processing, water purification and hygiene have all led to reduced exposure to certain harmless microorganisms. While this lack of microbial exposure has helped with keeping infectious diseases at bay, some suspect that the reduced exposure to live microbes may play a role in the increased prevalence of allergic and autoimmune diseases, along with obesity.
Early on in human evolution, the immune system, and particularly the immune system located in the gut representing 70% of the human immune cells, encountered large numbers of microorganisms through diet, but the industrialized diet of more recent times results in lower microbe consumption.
Scientists hypothesize that the human immune system has not had enough time to adapt to the current lower levels of safe, live microorganisms in the diet. And that could explain the rise in modern maladies that see the immune system misbehaving in response to foods (food allergies), the gut microbiota itself and even against our body (autoimmune diseases). For instance, inflammatory bowel diseases are characterized by an excessive immune response to gut microbiota, while in Hashimoto’s thyroiditis the immune system attacks the thyroid gland.
What can safe, live microorganisms in your diet do for you?
The hypothesis that dietary microorganisms might support human health is supported by many lines of thinking. The Nobel Prize-winning immunologist Ilya Metchnikoff observed over 100 years ago that Bulgarian peasants who ingested large amounts of fermented dairy products lived longer. Investigations into tribal diets full of fiber and live microbes compared to the low fiber, more sterile diets of industrialized people have shown marked differences in fecal microbiota, with associated differences in health outcomes. Finally, a couple of decades of controlled human trials on probiotics has shown that consumption of high numbers of at least some live microbes improves different health outcomes. These range from mitigating gut-related issues to protecting against upper respiratory tract infections and preventing atopic dermatitis. Even in healthy people, yogurt cultures can improve lactose digestion and some probiotics help with managing lower gastrointestinal symptoms.
Such observations converge on the idea that consumption of live microbes, including probiotics, may be a means of improving health, across the lifespan. This was suggested recently by a team of scientists under the auspices of ISAPP. These scientists called for an evaluation of available evidence as well as clarification of research gaps needing to be filled in order to address this hypothesis.
Fermented foods can contribute to increasing the diversity of healthy microorganisms in diets
One of the easiest ways to incorporate safe, live microorganisms into your daily life is through diet. Fermented foods, for instance, have been proposed to comprise a new addition to food pyramids in Canada, leading to a fifth food group beyond meat, vegetables, dairy and grains.
The next steps for scientists include developing databases that incorporate estimates of the numbers of living microorganisms in foods as well as compiling evidence currently known about consumption of live microbes and health. Long term, additional well-controlled studies are likely needed before dietary recommendations about consuming live microbes can be proposed.
Sanders ME, Merenstein D, Merrifield CA, et al. Probiotics for human use. Nutrition Bulletin. 2018. doi: 10.1111/nbu.12334.
Marco ML, Hill C, Hutkins R, et al. Should there be a recommended daily intake of microbes? J Nutr. 2020; 150(12):3061-3067. doi: 10.1093/jn/nxaa323.
Hill C, Guarner F, Reid G, et al. Expert consensus document. The International Scientific Association for Probiotics and Prebiotics consensus statement on the scope and appropriate use of the term probiotic. Nat Rev Gastroenterol Hepatol. 2014; 11(8):506-514. doi: 10.1038/nrgastro.2014.66.
Hill C. RDA for microbes – are you getting your daily dose? Biochem (Lond). 2018; 40(4):22-25. doi: 10.1042/BIO04004022.
Metchnikoff E. The prolongation of life, 1845-1916