For thousand of years humans have been using fermentation as a way of preserving foods and engendering good gut health. A fascinating new study from scientists at the University of Leipzig has discovered that a specific immune function receptor, uniquely evolved in humans and great apes, is triggered by a metabolite from lactic acid bacteria (LAB) found in fermented foods.

Most mammals have two kinds of hydroxycarboxylic acid (HCA) receptors. These receptors are known to regulate immune function and energy homeostasis, primarily in response to dietary conditions. Around 15 years ago a third HCA receptor was discovered in the human genome, which further research revealed to be unique to humans and great apes.

A new study has now discovered that one of the strongest activators of this third HCA receptor is D-phenyllactic acid, a metabolite produced by lactic acid bacteria which appears in some foods as the fermentation process takes hold.

So, if we rewind around 10 million years, to a time when humans, chimpanzees and gorillas shared a common ancestor, we find an era when this ancestor slowly started to spend more time on the ground instead of up in the trees. This new lifestyle meant our common ancestor started to eat more fruit off the ground, instead of freshly picked from a tree. The evolutionary pressure of eating less fresh food subsequently favored those better able to digest these naturally fermented foods.

As more LAB-fermented food was consumed, a new HCA receptor evolved to better process these novel bacterial metabolites. This new study further examined what physiological actions this third HCA receptor affected, finding foods that activate this process generate beneficial immune, glucose and insulin functions.

“We are convinced that this receptor very likely mediates some beneficial and anti-inflammatory effects of lactic acid bacteria in humans,” explains corresponding author on the new study, Claudia Stäubert. “That is why we believe it could serve as a potential drug target to treat inflammatory diseases.”

There is still plenty to discover about this unique receptor, which has not only been found on immune cells but also lung, skin and fat cells. Exactly how D-phenyllactic acid affects the immune system is still yet to be understood. So further research will hopefully uncover whether this specific process generally increases the body’s immune response to pathogenic bacteria, or simply suppresses the immune response specifically to allow lactic acid bacteria to survive.

However, it seems like this thought-provoking new discovery may offer insights into why certain cultures with long traditions of fermented food consumption seem to have lower incidences of bowel disease, and how we evolved to physiologically benefit from what essentially is old food allowed to harbor certain populations of bacteria.

The new study was published in the journal PLOS Genetics.

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