Is There a Problem with Gut Health?


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“Without doubt, the invention of the concept of gut health has created a tremendous boom for the wellness industry.”

The idea that nurturing your gut health can alleviate a variety of health issues—ranging from such diverse problems as certain skin issues, fatigue, indigestion, bloating, irregular bowel movements and anxiety to serious non-digestive concerns such as depression, colon cancer, Parkinson’s, Alzheimer’s disease and chronic liver disease—has gained widespread popularity in the lay press, social media and in scientific reviews. Social media is flooded with testimonials, and the market is teeming with products, from fermented foods to probiotic snacks and supplements, all promising to support gut health and digestive wellness.

For gastroenterologists, a healthy gut has always been a gut free of detectable structural, inflammatory changes or cancerous lesions, such as peptic ulcers, chronic inflammation (as in ulcerative colitis and Crohn’s disease) or tumors. In contrast, the new terminology of gut health implies that there are disorders of the gut that are not detectable with an endoscope, a CT scan or an X-ray but which may have widespread effect on our entire body.

“I firmly believe that the gut and its microbiome do play a central role in overall health.”

Reading a recent excellent article by Yasmin Tayag in the Atlantic Magazine made me think for a while about my own fascination with the “All Diseases Start in the Gut” quote attributed to the Ancient Greek physician, Hippocrates. Even though the statement makes every gastroenterologist feel proud that they picked the most important medical specialty as their profession, as a scientist, I have always been skeptical about any universal theory that explains the most complex medical problems with a single cause, the “string theory of disease”. However, based on my own research and an overwhelming amount of supporting information, I firmly believe that the gut and its microbiome do play a central role in overall health.

The importance of the gut to our overall health is undeniable. A rich and diverse microbial ecosystem inhabits our intestines, playing not only an important role in the digestion and assimilation of certain foods (composed of molecules too big for our small intestine to absorb) but also in the regulation of our immune, metabolic and hormonal systems. An extensive amount of experimental data obtained in animal models and to a lesser degree in human studies, strongly suggests that disturbances in this microbial ecosystem can not only lead to digestive ailments and immune system issues, but also play a key role in obesity, metabolic disorders, cancer and neurodegeneration.

“Diet plays a critical role in influencing our gut health and, in turn, our general wellbeing.”

Foods impact our gut microbiome, which then affects us; for instance, junk food is harmful to both the body and its microbial inhabitants. The simplest dietary advice that I have given to my patients over the years is to eat what is good for your microbiome and you can be sure it is good for your own health as well! In practical term, this means if you eat a diet rich in a variety of fruits and vegetables, you will ingest the very food components your gut microbes thrive on. These two food groups share the property that they are made up of molecules too large to be absorbed in our small intestine (like most other foods) and that the human gut lacks the enzymes to break them down into absorbable pieces. They contain complex carbohydrates (e.g. fiber) and polyphenols (large molecules which plants produce as their own medicine). Both groups are essential foods for the microbes which break them down into smaller molecules which serve as prebiotics nourishing the microbes.

“Microbes have lived in symbiosis with the gut of animals for millions of years…”

At the same time, the metabolites generated by the microbes from these molecules have direct health promoting effects on the gut and beyond, such as local and widespread anti-inflammatory effects. Interestingly, similar considerations apply to many health promoting ingredients in herbs and spices. This shared benefit for ourselves and the trillions of gut microbes in our gut shouldn’t come as a surprise. Microbes have lived in symbiosis with the gut of animals for millions of years, and both gut and microbes have been “fed” the same fiber and polyphenol rich diet for thousands of years. It is only with the advent of dramatic dietary changes in the industrialized world during the last 100 years, that this symbiotic relationship has been compromised.

Similar to plant-based foods, fermented foods, like yogurt, sauerkraut and kimchi are beneficial to our microbiome and our gut health because they increase the richness and diversity of the microbiome. When viewed together, there is no question that plant-based and fermented foods are good for the health of our gut microbiome, and a large amount of epidemiological data has demonstrated that they are good for our health.

“…supported largely by correlational studies but are incompletely understood.”

Similarly, the connections between a healthy gut microbiome, gut health and other health benefits, like weight management, mental health, and health of brain, liver and the large intestine, are supported largely by correlational studies but are incompletely understood. However, despite the assurance by social media influencers, it’s premature to assert definitive causal relationships between specific microbes, group of microbes or supplements targeting the microbiome and specific health outcomes.

For those without diagnosed gastrointestinal disorders, pursuing a healthy gut is a somewhat vague endeavor, with ambiguous targets. The food industry avoiding the critical eye of the FDA has capitalized on this trend with a myriad of “gut-friendly” products, yet many of these items offer unsubstantiated benefits. For example, probiotics in supplements may not always survive the journey to the colon, and the actual impact of prebiotic fibers can depend on the source, variety and quantity of the supplement. This being said, there are indeed a handful of high quality probiotic studies that have shown health benefits.

“…taking various supplements while consuming an unhealthy diet, devoid of fiber and polyphenols is an expensive way to promote a placebo effect.”

Despite the addition of fibers or live bacteria, inherently unhealthy foods don’t become healthy when with such an approach. The advice from experts is straightforward: consuming plenty of fruits, vegetables, whole grains, and legumes, and fermented foods, while avoiding junk foods, is a reliable path to good gut health and overall health. On the other hand, taking various supplements while consuming an unhealthy diet, devoid of fiber and polyphenols is an expensive way to promote a placebo effect.

This fixation with the gut isn’t new; it dates back to Hippocrates and is part of Aryurvedic and Traditional Chinese Medicine teachings. The appeal lies in its simplicity, suggesting a unified solution to many health problems and offering easy, self-manageable treatments. While a wealth of preclinical and epidemiological studies have shown unequivocal support for the gut health concept involving connections between diet, the microbiome, and overall health, the full extent of these relationships in humans, in particular the existence of causal relationships is yet to be established.

“…critical component of our overall well-being and diet plays a significant role.”

While gut health goes way beyond the traditional definition of absence of detectable gut diseases, it is a critical component of our overall well-being and diet plays a significant role. However, the current fixation on it, fueled by the industry and social media, needs to be approached with caution and a good dose of skepticism. As explained in detail in The Mind Gut Immune Connection and Interconnected Plates, a balanced, healthy diet combined with mind targeted approaches and regular, moderate physical exercise remains the best-known way to maintain a healthy gut throughout life and into old age.

Emeran Mayer, MD is a Distinguished Research Professor in the Departments of Medicine, Physiology and Psychiatry at the David Geffen School of Medicine at UCLA, the Executive Director of the G. Oppenheimer Center for Neurobiology of Stress and Resilience and the Founding Director of the Goodman-Luskin Microbiome Center at UCLA.