What does “gut health” mean?

By Prof. Maria Marco PhD, University of California – Davis

Probiotics and prebiotics are frequently marketed to consumers for their capacity to improve or support gut health. Dietitian nutritionists responding to a survey ranked fermented foods as the top superfood for the past six years explaining gut health as a primary reason for their choice. But what is gut health exactly?

As it turns out, there is not a widely accepted definition of gut health. Dr. Stephan Bischoff at the University of Hohenheim, Germany, nicely summarized the situation in a perspective back in 2011. Using criteria from the World Health Organization, he proposed that gut health be defined as “a state of physical and mental well-being in the absence of gastrointestinal complaints that require the consultation of a doctor, in the absence of indications or risks of bowel disease, and in the absence of confirmed bowel disease”. The term gut health has since been increasingly used in scientific publications. However, is gut health really only the absence of complaints or indications, risk, or disease? Is gut health a condition that requires physical and mental well-being?

For the first question, it seems reasonable that gut health would refer to an absence of bowel diseases and acute or even mild symptoms localized to the digestive tract such as food intolerance, abdominal pain, nausea, flatulence, bloating, constipation, and diarrhea. The etiology of these presentations can be traced back to disruptions in the normal functioning of the gastrointestinal tract, including undesired dietary nutrient breakdown and absorption, pathogen introduction and colonization, and intestinal inflammation. However, recent studies of the intestinal environment, encompassing both the intestinal microbiome and mucosa, suggest that an absence of complaints or disease does not directly mean our gut is healthy. Mild mucosal inflammation, increased barrier permeability, or the presence of certain potentially undesirable intestinal microorganisms may confer no overt symptoms, yet still could signify the presence of an undesired or unhealthy intestinal state. The outcomes of that imperceptible unhealthy state may not be realized until years later with the development of intestinal disease or conditions at extraintestinal sites.

This latter point evokes the second question: Is gut health a condition that requires physical and mental well-being? The answer from popular media is – yes! Diseases and chronic conditions that are not overtly related to the gastrointestinal tract, such as allergy, arthritis, obesity, cancer, mood disorders and depression, are now considered by many to be traceable back to gut health. To that regard, it is now well-established scientifically that our gastrointestinal tract is indeed an important organ, housing the majority of our microbiome and mucosal immune system and pivotal for systemic metabolism and neurological signaling. However, I wonder if the term “gut health” is at all appropriate when implying such a broad range of whole-body responses? Could it be that “gut health” is seen as the root or origin of our overall health?

One way to reconcile this broad interpretation of gut health is to consider that “gut health” has become a simple way to explain, interpret, and understand how diets intersect with overall physical and mental well-being. Our daily lives are structured around mealtimes and the foods we eat don’t just provide nutrients, but also social interactions, and can be affected by our socioeconomic status among many other factors. We connect our gut with sensations felt when hungry, full, and after drinking an alcoholic or caffeinated beverage. The gut also connects to diet-based risks for the development of non-communicable diseases over our lifetimes. The quote “all diseases begin in the gut” attributed to Hippocrates still rings true after all the medical advancements over the past 2400 years.

So, since the term “gut health” has such a broad interpretation, we should be qualifying any statement that a biotic or fermented food supports “gut health” with an explanation for the specific feature(s) of gut health that are being improved with biotic use. Perhaps in the future, good gut health, and even good health generally, can be defined. Until then, we only appreciate how we are starting to get closer to understanding the true interconnectedness of the diet-gut-microbiome axis with our overall health and well-being.