Digestive System: An overview of function and process.

What is the digestive system?

According to Stephen Macallan the digestive system is the engine that drives the body and whatever our goal might be (better health, bigger muscles, leaner and stronger muscles, losing/gaining weight, maintaining health), the first step must be the digestive system.

The digestive process begins with the sight of food – merely looking at an appetising meal will trigger an assortment of mechanisms (unless one is already satiated with food) – saliva will be released by the salivary glands, the gall bladder will contract and squirt some bile into the stomach and bowel and the pancreas will start to create some enzymes in preparation for the imminent arrival of food.

Food divides into four main categories – proteins, carbohydrates, fats and fibre. Let’s look at this in a bit more detail:

The things we digest: components of foodstuffs


Proteins are, any foodstuff derived from an animal - meat, fish, eggs, milk/cheese, and there are proteins of vegetable origin – principally legumes and nuts. It used to be that animal proteins were called first class proteins and vegetable proteins were called second class proteins – this classification is not popular these days due to the rise in the number of people following a vegetarian or vegan lifestyle but the core of that classification holds true today. Animal proteins readily provide all of the amino-acids that we need and it is a little trickier to obtain all the amino-acids that we need from vegetable proteins only.


Carbohydrates are found in most other foods in varying proportions but it is most useful to think of carbohydrates as being the 'starchy' foods - cereals, such as rice, corn, oats and wheat, these are the ones we know mostly in the West. Less well-know cereal carbohydrates are buckwheat, millet, sago, tapioca, quinoa (higher in protein than than the others), sorghum and triticale. In addition there are vegetables which are high in carbohydrates, principally the root crops - potatoes, parsnips and swedes. An interesting historical note is that for hundreds of years wheat was comprised of approximately 90% protein and a mere 10% starch and was a good food. Then about 120 years ago farmers began to cross-breed different strains of wheat, a process called hybridisation - producing larger ears of wheat, wheat that managed with poorer soils, coped with drier climates, grew faster, and so on. The result is that wheat nowadays comprises 90% starch and only 10% protein and is far from a good food. It can be argued that the extreme hybridisation that wheat has endured has created a 'novel' food and as such humans are no longer adapted to it - hence the increasingly common situation of people becoming allergic to it.


Fats are properly called Essential Fatty Acids and there is a vast amount of misunderstanding about EFA's. We live with an increasingly overweight population - fat people. The idea has arisen that eating fat makes you fat - total nonsense - in fact carbohydrates make you fat. Fat does not make you fat. However there are good fats and there are bad fats. Good fats are; cold-pressed, unrefined and non-hydrogenated vegetable oils - such as olive, sunflower, sesame, walnut and the king of good fats is coconut butter. Soya is a bad fat and indeed is an all-round bad food and should be avoided. Rape and Canola are not exactly bad fats but they are poor quality fats and best avoided. Animal fats are good fats as long as they are grass-fed and organic otherwise animal fat is a bad fat.


Fibre is everything that is in food that is not protein, fat, sugars, minerals and vitamins. Fibre is what is left when all the 'good stuff' is extracted from the food and is a fibrous substance that provides bulk to our diet. Bulk is important, it gives our digestive system something to work with, providing a stimulus to peristalsis and providing something for our bodies to drop toxic material into for elimination in our daily bowel motion .


The digestive system is also responsible for breakdown and absorbption of micronutrients. Micronutrients are nutrients such as minerals, vitamins and antioxidants that are only needed in miniscule quantities relative to that of macronutrients.

Protein digestion

The digestion of protein begins in the stomach in the presence of hydrochloric acid and pepsin – these two compounds break the bonds in the protein structure and reduce the complex nature of protein down to polypeptides, which enter the small intestine where further enzymes break the polypeptides down to shorter and shorter chain peptides until they eventually become single peptides which the body can absorb and then re-assemble into the various proteins which make up our body. For this process to function correctly we need a, healthy liver/gall bladder (for the bile, HCL and pepsin), pancreas (for the trypsin and chymotrypsin digestive enzymes), stomach (to mix it all up) and small intestine (breaking it down and absorbing it).

Carbohydrate digestion

Carbohydrates meet amylase in the saliva in the mouth – chewing and amylase begin the process of breaking carbohydrates down from complex sugars, polysaccharides, into simpler sugars, mono and diglycerides. In the stomach the acid neutralises amylase and it is not until the carbohydrates enter the small intestine that more amylase begins to work on the polysaccharides eventually producing diglycerides and then lactase, sucrose and maltase convert digylcerides into monoglycerides which can be absorbed by the small intestine.

Fat digestion

Fats do not mix with water and in the presence of water, fat coalesces into larger and larger globules and in the watery environment of the digestive system large globules of fat are indigestible. In order for our digestive system to process fats the fats must be emulsified into smaller droplets and this is achieved by bile salts and phospholipids in the small intestine. Once the fat has been emulsified into small droplets then the lipase can get to work on the fat droplets and break them down into micelles – these micelles can pass into the villi of the small intestine where they are further processed into lipo-proteins and then they enter into circulation in the body. For this process to work correctly we need a healthy liver/gall bladder (for production of enzymes) and a healthy small intestine (for emulsifying, digesting and transporting fats.

The importance of flora and probiotics for a healthy digestive system

The last four paragraphs detail the process of digestion as it has been understood for many years and represent the current thinking of mainstream science. However mainstream science is 15 – 20 years behind the leading edge of scientific thinking. In the last 10 – 15 years the importance of the gut bacteria has come to the forefront of the science of our health – some experts are saying that our gut flora represents 80% of our immune system. It is now emerging that the gut bacteria produce enzymes that are involved in the metabolisation of all the above four food groups and that the enzymatic processes discussed above are only half the story.

irritable bowel syndrome and gut flora

Approximately 40% of the population of the UK suffer with some aspect of irritable bowel syndrome according to the latest research – that’s a lot of people! The symptoms of IBS are many: constipation, diarrhoea, flatulence, pain and discomfort, bloating, indigestion, reflux and so on. Medical diagnoses that end in syndrome are medical jargon for ‘haven’t got a clue’, meaning that orthodox medicine does not have an identifiable cause for the symptom picture. In my experience IBS always includes dysbiosis as one of the causative factors and in many cases it is the only causative factor.


Dysbiosis means a disorder of the biome or the gut flora. The gut comprises 36 feet or so of tube, 32 feet of small intestine and 4 feet of large intestine and this 36 feet of tube is home to a complex ecology of bacteria, and it is an ecology! It comprises a delicate balance of upwards of 1000 different species of micro-organisms inhabiting different sections of the tube/bowel, each organism having a particular task/role and working hand in hand with the various enzymes that our organs produce.


The world we have created is a world where these micro-organisms are ignored and forgotten about and many aspects of our western culture represent a threat to the well-being of our biome – threats such as:

The main other biome-compromising factor is our mother – at birth, our mother provides the ‘seed’ from which our biome will bloom and our mothers and grandmothers and even our great-grandmothers (depending on our age) will have been exposed to those same threats in their lifetime before we were born and so, their biome was already compromised before our birth. Thus the ‘seed’ from which our biome grew was already impaired, and if her seed was impaired from her mother’s compromised biome, well….. need I go on?

This is the reason for the increasing prevalence of allergy related illness and bowel disorder in children and young people today. Without a major wake-up by all and sundry the situation will only get worse.

The digestive system is the engine that drives the body. If the digestive system is in disorder, nothing else will work properly, so anyone striving to better their health in any aspect whatsoever must start with the digestive system. If we want to be healthy we have to have a good digestive system.

Article by holistic healer Stephen Macallan.