Leaky gut is a term that is often over used and without much consideration for the pathology behind it.
Leaky gut refers in the main to a condition that can occur in the hindgut, in horses involving the caecum and the large and small colon. The hindgut is the area of the digestive tract where fibre is broken down by bacteria fermentation and converted to Volatile Fatty Acids (VFAs), which are absorbed across the gut wall and are a valuable source of energy for the horse.
This process requires a healthy mix of bacterial populations, often referred to as the gut biome. There are many factors that can disrupt this biome, including disease, excessive or poorly digestible sources of carbohydrates in the diet, certain medications, stress, rapid changes to hard feeds or fibre sources. Any disruption can cause the rapid proliferation of a group of these bacteria referred to as ‘Amylolytic ’. This group of bacteria unfortunately produce both VFA’s and Lactic Acid.
As the Amylolytic bacteria build in number the hindgut becomes acidic, rather than the normal neutral or slightly alkaline environment. This change of pH to acidic, causes the death and destruction of the other bacterial populations within the hindgut biome. This then reduces competition for space and nutrients and the Amylolytic bacteria levels can increase further and lactic acid concentrations to build. The death and destruction of the other bacterial populations also results in endo and exo toxins being released into the hindgut.
The presence of increasing lactic acid and these endo and exo toxins within the gut then results in the irritation of the gut wall. The gut wall is a complicated structure, but fundamentally it’s role is be provide a selective semi-permeable wall between the blood/abdominal cavity and contents of the gut. Allowing nutrients and water to be absorbed, but to block the transfer of harmful substances contained within the digested materials.
Irritation to the gut wall can impede it’s ability to perform this function. If the irritation to the hindgut wall is significant enough it will result in inflammation. This inflammation causes the swelling and stretching of the gut wall, pulling the cells of the gut wall further apart. As the space between these cells increase so to does the permeability of the gut wall. Allowing for molecules that would normally be blocked from ‘leaking’ out of the digestive tract, including the lactic acid and toxins. Once no longer contained within the digestive tract these molecules can have a system impact.
Consider the image of a partially blow up balloon, now imagine drawing a series of squares bunched up close to each other on it’s surface, forming a solid wall appearance. Now if you were to imitate inflammation and blow that balloon up further, those squares would stretch away from each other and the gaps between these squares would become obvious. While this is a simplified explanation of how inflammation of the gut wall creates ‘spaces’ for molecules to leak through, I feel it’s a good visualisation example.