Many everyday foods—from yogurt and other fermented foods to fresh fruits and vegetables—contain live microorganisms. And although humans have consumed these safe and potentially beneficial bacteria in their daily diets for millennia, live microbes have received much less attention than other components of the diet. With a rising global awareness of the importance of gut health, many people believe intake of live microbes is health-promoting, but so far it has not been possible for experts to create a guideline on how many we should be consuming on a daily basis.

A group of seven interdisciplinary scientists recently published a review paper in The Journal of Nutrition, titled: "Should There Be a Recommended Daily Intake of Microbes?" They explain that only weak evidence to date confirms the link between live microbes and better human health, highlighting specific gaps in the research and laying out a plan for quantifying the relationship between consumption of live microbes and health outcomes across populations.

In the review, the authors outline why this scientific endeavor is worthwhile, but far from straightforward. Challenges include the scant records on consumption of microbes in past human populations; frequent mis-reporting of dietary intakes in current nutrition research; and the complex biology of the digestive tract, which makes the mechanisms of microbial health benefits difficult to discover.

"People frequently hear that they should keep adding 'good microbes' to their gut microbiomes," says Dr. Mary Ellen Sanders, co-author of the paper and Executive Science Officer of the International Scientific Association for Probiotics and Prebiotics (ISAPP). "This makes intuitive sense, but it's important to build up the scientific evidence for the idea rather than just assume this is true. Our paper is a call for scientists around the world to start building the evidence base in a rigorous way."

The publication builds on a discussion group held at the 2019 ISAPP annual meeting in Belgium, which aimed to explore evidence that live microbes in general—and not only the bacterial strains that have special status as probiotics—form an essential part of the human diet.

"Currently, food guides around the world do not recommend daily intake of live microbes," says Sanders. "Although continual doses of live microbes may not be critical for our survival, by ignoring them we may be missing out on an important opportunity to support the health of different populations."

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