The last few years have seen a marked paradigm shift in the way that medicine views the link between digestion and health. Gradually we are realising just how critical gut health is to our immune system impacting autoimmune conditions in particular. Between 70-80% of our immune system is located in the gut and in an area that is so susceptible to damage when lifestyle and digestion are out of whack, it is no surprise that impaired digestion system is directly related to the development of autoimmunity.
This article will examine how an impaired digestive system can lead to “leaky gut” and ultimately autoimmunity.
Defining the gut
The gut refers to the hollow tube that connects the mouth to the anus. The entire digestive process takes place between these points with food being broken down, nutrients absorbed and waste excreted. The gut is supposed to be an intact passageway that prevents food particles from entering into the blood stream. However, a plethora of lifestyle factors such as stress, inappropriate foods, not adequately chewing our food, can lead to an impaired digestive system, and in turn a damaged gut. When the gut is damaged and not able to perform the most critical role of separating food from the blood stream our immune system becomes compromised.
The importance of healthy upstream digestion
When working effectively the role of the mouth, stomach, pancreas, liver and gallbladder is to adequately pre-digest food so that the particles are very small once they reach the intestines. In a healthy system food will be chewed properly, stimulating both mechanical and chemical digestive processes before the bolus (chewed food) travels down the oesophagus. The stomach should be an environment that is very acidic, a pH lower than 3, which enables significant break down of food as well as destroying any bacteria that might have made it into the stomach. This acidity is very important but unfortunately low stomach acid is very common. Once the chyme (digested food) leaves the stomach via the pyloric sphincter, proteins should be broken down into amino acids and short polypeptides; carbohydrates should be monosaccharides; and, finally the bile released by the gallbladder in the duodenum further emulsifies fats. If stomach acid is not sufficient then the problems become two fold – solid particles can make it into the small intestine and bacteria that should have been destroyed can also pass through into this very sensitive area.
In a healthy digestive system the above processes will enable the delivery of small particles to the small intestine where 90% of nutrient absorption takes place. To enable absorption of nutrients in the small intestine, the surface of the tract is lined with millions of epithelial, (meaning slightly permeable) cells. These cells are referred to as villi and microvilli, which are folds of cells that increase the surface area of the small intestine to maximise nutrient absorption. The villi allow nutrients to be absorbed through tiny spaces and sent off into the blood stream so the body can feed the nutrients to the cells. Fats are also absorbed and moved into the lymphatic system.
Lymph nodules called Peyer’s patches also line the intestinal walls and have the job of killing bacteria that has made it into the intestines from the stomach. They act as a kind of filter and should remove bacteria from the nutrients to ensure that only the required nutrients are absorbed into the blood stream. Peyer’s patches also line the large intestines. When digested chyme moves through the ileocecal valve into the large intestines, which is home to an incredibly diverse range of bacteria. Here the “good” gut flora should offset any remaining “bad” bacteria that have made it this far down the digestive process.
Leaky gut – where things go wrong
The permeable nature of the intestines means that the walls are prone to damage. When food particles are not adequately digested upstream due to inadequate chewing of food, low stomach acid and insufficient bile to break down fats, intact particles can make it into the small intestine. These particles can damage the lining of the gut leading to intestinal permeability, a common condition that is colloquially referred to as “leaky gut.” When the gut is leaky food particles are no longer correctly filtered through the intestinal walls into the blood stream, but can escape through the holes between the villi lining the walls.
Leaky gut can develop as the result of undigested food particles entering the intestines but can also be an inherited condition. The intestinal wall may be inadequately formed as the result of a Caesarean section birth, lack of breast-feeding during infancy or inappropriate foods being fed to an infant prior to the gut being properly formed, which can take up to two years. Breast-feeding actually promotes formation of the intestinal walls and should be encouraged. Leaky gut can also develop as the result of alcohol consumption, chronic stress and medications including antibiotics and non-steroidal anti-inflammatory medications, all of which damage the intestinal wall.
Correct vs incorrect nutrient absorption
Nutrients should be absorbed through the epithelial cells that line the intestinal walls. However, there is a fine balance between what is sufficient nutrient absorption and what is too much. When peptides are absorbed through the correct epithelial cell channels, the body recognises them as the amino acids ready for performing their many functions throughout the body. In this case the body correctly perceives these amino acids as friend, not foe. However, if these peptides are able to sneak out through the holes between epithelial cells lining the intestinal walls, then the body perceives them as foreign invaders and will launch an attack to prevent the “invader” spreading. If a protein escapes and is recognised as foreign, the body may also develop an acquired immune response. This means that on future occasions when the protein is consumed also become targets for an immune response. Wheat, dairy and soy are problematic foods for many people because the gluten, casein and soya proteins respectively can cause the body to launch an attack on these proteins. The medical definition of an allergen is anything that is protein-based; however, the body may also perceive non-protein molecules that escape the gut as foreign invaders that must be countered. If the body is constantly on high alert and attacking proteins then ongoing inflammation and autoimmunity can ensue.
Gut dysbiosis worsens the problem
Further compounding links between gut health and autoimmunity is the fact that gut bacteria is critical to the health of the epithelial tissues that line the intestinal walls. Without a correct balance of gut flora, the epithelial cells will not regenerate which ultimately worsens leaky gut. Furthermore, so-called “good” gut bacteria are essential in destroying pathogens that make it into the intestines. The predominant type of antibody that lines the gut is IgA, which is supported by an abundance of “good” bacteria. Without this supporting balance the body’s ability to destroy pathogens in the gut is impaired and these pathogens are able to escape into the blood stream further increasing the need for a strong immune response.
An allergic reaction is the body doing its job in preventing the spread of foreign bodies; however, when these reactions are to food the immune response can be overplayed. This is when autoimmune conditions can arise. If a person is consistently consuming proteins that escape the gut and their body is attacking then the body will constantly be on high alert and inflamed. This overactive immune state can ultimately lead to autoimmunity as the body becomes used to attacking substances that are always present in the body. The immune system can mistake parts of the body as a pathogen and attacks its own cells as though they are “non-self.”
Common autoimmune conditions include:
1. Coeliac disease, where the body attacks the villi lining the small intestine;
2. Rheumatoid arthritis, the immune system attacks the joints; and
3. Multiple Sclerosis, the immune system attacks the myelin sheath of nerves leading to neuro-degeneration.
We are seeing a growing body of anecdotal and empirical evidence that reducing inflammatory foods in the diet and improving gut health can have very positive impacts on these autoimmune diseases. When the body is not constantly under stress from foreign particles in the blood stream then the overall immune response is lessened thereby improving the condition.
The digestive sytem impacts every other cell in our body. Look after it.
This article has explored the very strong links between digestive health and autoimmunity. As a critical foundation to health the digestive process can be a source of great nourishment or if damaged, a source of great stress to the body. This is why consuming a properly prepared, nutrient dense diet that is low in inflammatory foods such as gluten, diary and soy is critical to the prevention and treatment of many autoimmune conditions. Additionally, from my own experience although I do not have an autoimmune condition, since adopting an anti-inflammatory diet I have seen marked improvement in my own immunity. No longer do I get bronchitis and flu multiple times each winter, but feel more energetic and vital.
Hippocrates was very much right when he said so many years ago: “All disease begins in the gut.”