Guest Post


“All disease begins in the gut” – Hippocrates

It turns out he may have only been half right. All diseases begin in the mouth.

In recent times we’ve learnt so much about how our gut influences our health. The scientific breakthroughs in understanding the human microbiome have revealed the amazing role of microbes that live inside our digestive system. Research is now finding connections between diseases like digestive, autoimmune, metabolic and mental degeneration may all have a common cause of bacterial dysbiosis.

However amongst all this conversation, there’s been one notable omission. Our mouths.

Dentists have long known the bacterial basis to dental disease. They’ve also long been stressing the way the mouth links to the body and our overall health. However, new knowledge of the oral microbiome may reveal exactly how dental disease is a serious sign of problems all over our body and the intimate relationship between nutrition, our mouth and disease.

Oral microbiome – our connection to the world

There aren’t many of us who could say we’ve never missed a dental appointment. Our teeth are often the victims of neglect; however, skipping that trip to the dentist may mean that you’re missing crucial contributors to your overall health.

Until the mid 90s, general belief centred around all bodily fluids being completely sterile. By sterile, we mean without the presence of microbes. What a naïve world we lived in.

Our body has since been shown to be crawling with bacteria, so much so they outnumber our own cells 10 to 1. Living in separate, related, yet distinct populations, the human microbiome includes our skin, gut and you guessed it, our mouths.

The entire length of our digestive system is populated with trillions of microbes, with the mouth and the stomach containing a 45% overlap between species.

At birth, these tracts are sterile and the mouth is the first point of colonisation of bacteria. It then proceeds to manage and ‘seed’ the gut population.

During the first two weeks after birth, oral and stomach microbial populations are identical, before eventually establishing themselves as separate functioning entities.

However, throughout life they remain in constant communication with the mouth acting as a kind of ‘bodyguard’ that screens and ushers only suitable bacterium to the gut population.

How dental disease disrupts the gut

Got a hole in your tooth? No big deal, a filling will plug that up right away. Problem fixed. Right?

Well, it turns out there may be more to it than this.

It’s estimated that swallowed saliva carries around a trillion bacteria into the body everyday. Overgrowth of harmful species in the mouth provides a continual source of these microbes to the gut, a likely starting point of imbalance throughout our entire digestive system.

Early research is showing how species known to be largely present in gum disease will colonise the gut bacteria at late stages of other diseases such as diabetes and may play a role in obesity.

As microbial sequencing techniques improve, it may not be long before a simple saliva test at the dentist enables us to gain an indication of how our diet is influencing the health and function of our entire microbial population.

How food affects your teeth first, then everything else after

Tooth decay is a dietary driven disease where the mouth environment is overwhelmed by bacteria that thrive on metabolising simple carbohydrates and producing acid.

Scientists who measured fossilised dental plaque from our ancestors revealed that modern human mouths have undergone a significant loss in diversity.

This has coincided with the proliferation of disease causing bacteria, due to the large-scale consumption of processed flour and sugar that happened to pop up right at the time of the agricultural and industrial revolutions.

Are carbohydrates the enemy?

Dental diseases like tooth decay which popped up since we began to eat the modern industrialised diet seem to teach us a stern lesson about food. We’ve all heard that sugar causes tooth decay, but there’s more to it than this. Sugar is a form of simple carbohydrates that feed a certain type of bacteria in your mouth.

The reason why dental disease (and other problems associated with gut health) were so little known in traditional societies was because they consume food in their natural form. In the wild, sugars are encased in complex carbohydrate walls called ‘cellulose’ which makes up the basic structure of the plant world. Also known as fiber, these complex carbohydrates are indigestible to humans – when we eat them they pass through our system untouched.

The main difference between ancestral carbohydrate intake and our carbohydrate intake today is that their dietary sources were nearly solely delivered encased in cellular carbohydrates in the form of fibrous cellulose. Modern processing of foods strip the fibrous coating away to create foods such as rice, grains, wheat and of course, sugar. Even though we can’t digest dietary fiber found in fruits and vegetables, it is essential for health, with both soluble and insoluble fiber regulating the digestion process and promoting bowel movement.

Feeding your inner factory

We’re not the only ones who use carbohydrates as fuel. Trillions of bacteria, referred to as the microbiome that live in our mouth, gut and intestines, also feed on carbohydrates and depend on us ingesting them for their own metabolic processes.

What’s really interesting is that our body’s entire ecosystem of bacteria evolved to simultaneously digest our food. This microbial population is designed to break down carbohydrates from natural, whole foods. A vegetable, for example, requires slower digesting microbes to move in, break down the cellulose casing and release the simple sugars to feed other bacteria and of course the human.

How processed food change our bacteria

A diet too high in simple carbohydrates will shift the microbial populations to favour the bacteria that feed on these smaller molecules. In the mouth when we eat too much sugar, a bug called Streptoccocus mutans overgrows, releasing acid and resulting in tooth decay.

In your stomach, shifts in the microbiota have been shown to cause leptin imbalance as well as low-level inflammation, both markers of weight gain. Add this to insulin release and you’ve got the perfect environment for obesity and the true reason as to how modern carbohydrates trigger weight gain.

Much of the negative image around carbohydrates is due to the fact that we have consumed the modern processed version of them for so long. Simple, acellular carbohydrates like flour and sugar change our microbiome, which forms the likely connection to insulin driven metabolic disease and weight gain.

French paradox: why cheese and wine are healthy

In the 1980’s, whilst the Western world was rolling out the low-fat craze, it was noticed that the French were doing everything that doctors were telling us not to do. Instead of pining over low-fat high sugar food they kept eating their traditional high fat cheeses – and drank lots of wine while they were at it.

Despite low levels of exercise and high rates of smoking, they had half the rate of heart disease and live 2.5 years longer. For years researchers were stunned with the paradoxical nature of French health outcomes when they directly contradicted the supposed ‘known’ risk factors for coronary heart disease.

It was later hypothesised that their secret to longevity was due to higher levels of red wine consumption in France – which was eight times that of the average Americans at the time. The theory suggested that wine negated the fact that their diet was high in saturated fat, with the French estimated to eat 24 kg a year per person which is nearly double that of the average American and Brit (13kg).

Traditional cultures are known to have a higher intake of fermented foods rich in bacteria and the French diet is an excellent example of this. Winemaking is a careful process of fostering bacterial fermentation reaction by the family of lactic acid bacteria. Malolactic fermentation can aid in making a wine “microbiologically stable” in that the lactic acid bacteria consume many of the leftover nutrients that other spoilage microbes could use to develop wine faults. It’s thought that it creates a rounder, fuller mouthfeel, which may show that our tastebuds are designed to be drawn to the presence of microbes.

The French language has 27 different words describing the different tastes of cheese. It doesn’t take long to see why – with their rich cheese culture it’s estimated that across the country they have a thousand different varieties with many of the traditional cheese making practices protected by law.

French cheese differs from that of other Western countries in that the majority is consumed as real cheese purchased from the shop rather than added to processed foods. Of the top 10 best sellers, at least four cheeses are unpasteurised, as it’s common belief that this gives them more taste and special properties.

The most well known and respected cheese making processes are notably less sterile as it’s known that increased diversity of microbes including moulds add to the tastes and textures compared to industrial preparations of cheese. They contain a staggering variety of microbes including bacteria, yeasts and fungi with hundreds of species – most of which are unknown.

Some types of cheese are known to arrive with chubby mites crawling and gorging on the cheese they’re living within. Interestingly, cheese-related food poisoning is very rare. The complex tradition around making cheese is known to involve cheese regularly rubbed with a milky rag from a vat on the floor of a cellar to give it a good crust due to the presence of bacteria and fungi. This milky rag is known to be dipped in other substances like horse urine to give it distinctive flavours and a sensory experience!

How bacteria were lost in our nutrition

Across the world people were known to eat a high amount of fermented foods. The Romans ate sauerkraut, the Indians would have lassi as a pre-dinner yoghurt drink. In Bulgaria incredible health was seen through the consumption of raw fermented milk and kefir. Across various Asian countries it was pickled vegetables of all types. Chinese workers were known to eat acid-fermented vegetables while building the Great Wall of China. Centuries ago, the Koreans developed kimchi by acid-fermenting cabbage and other vegetables. Today African cultures still routinely use lactic acid-fermentation as a way of preserving crops like corn.

It’s no coincidence that fermented foods were consumed across the globe in all civilisations. They are chock full of probiotic bacteria as well as prebiotic fibres that we know feed the entire microbial colony.

The key lies within the chemistry of Lactobacillus bacteria which have the ability to convert sugars into lactic acid. These bacteria readily use lactose or other sugars and convert them to lactic acid. Lactic acid is a natural preservative due to it inhibiting the growth of harmful bacteria. It also increases or preserves the enzymes and vitamins improving digestibility.

When fresh vegetables weren’t as readily available throughout the year, they were often preserved through fermentation. Due to improved transportation and storage, vegetables are available all year around; whilst refrigeration and canning have become the methods of choice. Whilst convenient for retaining vitamin content, they lack many of the crucial elements that fermented foods provide to feed our mouth and gut microbiome. Dairy is boiled and homogenised and plants sprayed with fertilisers and therefore we’ve lost the connection to the intricate bacterial processes of food.

Feed your mouth and gut bacteria with fermented vegetables

Today with good quality raw dairy very hard to get our hands on, an alternative is to eat a small serving of fermented vegetables with every meal you can. If you’re purchasing fermented vegetables it’s important to note that cheap jars will usually be devoid of any live bacteria. Good quality fermented vegetables should be packaged in glass not plastic, submerged in juices and refrigerated. They should be cultured for a minimum of 10 days and cured in the fridge for 6-8 days.

Make your own fermented vegetables

  1. Use organic vegetables like carrots, peppers, kale, seaweed, collards, broccoli, and celery for the brine.
  2. Juice the stalks of celery to create the brine. The sodium in celery helps to encourage the growth of bacteria.
  3. Put the vegetables and celery brine in an airtight jar; make sure to fill to the brim. Optionally you can add some herbs of your choice for taste. Then cover the mixture with a cabbage leaf.
  4. Seal the jar and keep in a warm, slightly moist place for 2 to 4 days, such as a portable esky filled with warm water to store the jars. Alternatively warm wet towels can be used to cover them and set them in a casserole dish filled with warm water. Maintain a temperature range 20 to 25 degrees celcius.
  5. After several days, move the jars to the refrigerator to be stored ready for consumption.

Dr Steven Lin Bio

Dr Steven Lin is a dentist, health writer and speaker with a background in biomedical science and nutrition.

He is the creator of A resource that merges dental, nutritional, and ancestral medicine together as a unified model of functional health.

Currently he is writing the publication ‘The Dental Diet’: an exploration of evolutionary diet, genetics and nutritional science. Based on the pioneering work of Dr Weston A Price, Dr Lin explores the link between modern industrialized food, dental disease and chronic degenerative health problems.

You can follow him for dental, food and lifestyle tips @DrStevenLin on Facebook, Twitter or Instagram.