The Oral-Gut Connection

Taylor Fazio, MS, RD, CDN

I’ve been spending a lot of time recently deep diving into the origins and history of oral health. And something kept coming up over and over again: an obvious but often overlooked relationship between oral and gut health. In honor of Oral Health Month, let’s make the connection. We’ll start all the way at the beginning.

In the beginning: our ancestral diet

According to the WHO, dental caries (the fancy term for tooth decay or dental cavities) is the most common noncommunicable disease worldwide, affecting 92% of adults. But it hasn’t always been this way: dental caries is a modern phenomenon.⁠

Hunter-gatherers predominately ate root vegetables, meats, and fruits, rich in prebiotic and probiotic bacteria that feed the ecosystem of the gastrointestinal tract. Our ancestors relied on a diet that required arduous chewing, due to lack of cooking and food manipulation techniques. For that reason, fossils dating back to the Paleolithic era show bad tooth mineralization, and the occasional poor dental alignment, but very little dental caries. ⁠

New food club: modernization of diet

As the modern diet evolved to include quick, shelf stable, highly processed foods, oral health and gut health started to see a negative impact. Foods became softer and less nutrient dense, decreasing the need for thorough chewing. The impact soft palatable foods had on dental health wasn’t really well understood until recently. Without the need for prolonged mastication, human dental alignment began to shift and narrow. (Fun fact: nearly all animals on the planet — with the exception of pugs and other short-snout dogs — have relatively perfect dental alignment without dental hygiene interventions, thanks to their natural diets). The shift toward a more processed diet also altered the oral and gut microbiome, leading to greater levels of destructive bacteria and a sharp decline in immune function. 

Price is right: tying food to oral health

In the early days of modern dentistry, nutrition was a big part of regular curriculum. Over time, the industry started to shift its focus from prevention to treatment. Weston Price (1870-1948) played a significant role in developing the Westernized approaches to holistic dentistry seen today. In a quest to understand how diet impacted teeth, Price traveled the world to indigenous cultures where teeth brushing was not a common practice, but where whole, real foods composed most if not all of their diets.⁠

Priced noted main culprit of poor dental health was our modern diet: white flour and rice, packaged pastries and baked goods, refined sugar and jams, canned and chemically preserved goods, and processed vegetables oils. The common thread between these foods? They require little to no chewing, have high sugar content, and create a suboptimal oral environment. When we eat refined carbohydrates, sugar mixes with the natural bacteria in our saliva and creates acid, driving up the pH level and leaving us with a more acidic oral environment.⁠

Price’s conclusion: getting rid of refined grains and added sugar, which are highly cariogenic, can help oral health. The piece he didn’t connect was linking the importance of oral health to other systems in the body, specifically gut health…stay tuned.⁠

Head bacteria in charge: exploring the microbiome

The flora of the mouth and gut have changed significantly over human evolution. The types of food our ancestors consumed proliferated different bacteria for the specific digestion of their hunter-gatherer diet. These bacteria have now migrated into different parts of our GI tract. Visitors from the oral microbiome reach the stomach through swallowed saliva, food, and beverages. In general, these bacteria aren’t great at colonizing a healthy GI tract. In severe diseases, however, increased amounts of oral bacteria have been reported in the intestine (i.e.: IBS, liver cirrhosis, colon cancer, gastroesophageal reflux disease, and alcoholism). Diseases associated with periodontal disease are also associated with imbalance of the gut microbiome. Impairment of the gut barrier function and modulation of the gut immune profile induced by oral bacteria-mediated gut dysbiosis result in systemic inflammation.

TLDR: your oral microbiome can act as the lobby for your gut microbiome. You are what you eat.⁠

One-tract mind: the oral-gut health connection

Did you know the GI tract runs from the inside of your lips to the end of your colon? The bacterial communities present in the human body play a critical role in many functions including: digestion, metabolic regulation,  detoxification, immune system, and more. Maintaining good oral health through hygiene practices can prevent gut dysbiosis-associated diseases such as metabolic, inflammatory, and autoimmune disorders. Oral bacteria are associated with several systemic diseases. Recently, their association with inflammatory bowel disease (IBS) and colorectal cancer has attracted the most attention. To flip the switch, gut health is just as important for oral health (for example, a classic sign of gut dysbiosis is bad breath).

Since the tract is one long tube, symptoms can manifest in different areas. So when you take care of your gut health, you’re taking care of your oral health, and vice versa. That’s what we call a two-for-one deal.⁠