Digestion 101: this might be why you have digestive issues

Have you ever been told you've got digestive issues?

Or that you might be low in iron?

Maybe you feel that you're not absorbing properly?

Someone might of even said "you need to take digestive enzymes."

But what actually do any of these things mean?...

To understand the how and why things go wrong in the digestive system you must first understand how it works.

Often just thought upon as the body’s internal plumbing, the digestive system plays more than a number of essential roles within the human body. One of the most important being food digestion.

“Good health starts in the gut”

It is here that your inner body first meets the external world…

It is here that your microflora flourish…

It is here that your immune system dominates…

And it is here that all essential nutrients are extracted and absorbed...

All of which are influenced by proper digestion.

Eating food provides us with one or more of the nutrients required to nourish our bodies. Essentially we need six classes of nutrients for normal functioning. These include: carbohydrates, lipids, proteins, vitamins, minerals and water.

For the body to use these nutrients, the foods we consume must first be digested.

Digestion = breaking down food mechanically and chemically.

Did you know… that the lining of your digestive tract is actually super thin. If you took a strand of hair, snapped it in half and compared it to the digestive tract lining, that snapped hair end would still be thicker. Consequently, there’s not much separating your internal body from the external world. Another reason to take care of your gut health.

Now considering your digestive tract has quite some length in it, accounting the distance from your mouth to anus (about 10m in length), as well as the millions of villi (I’ll explain soon) that cover it, you will find that it therefore has a great surface area. Laid out flat, it would cover the size of a tennis court, which is about 250 square metres. This large surface area is of utmost importance regarding its capacity to digest and absorb normally.

Contrary to popular belief, you are more than what you eat… you are what you digest, ferment and absorb. On average, a human like yourself will eat around 800 to 1000kg of food each year; that's up to 100,000kg of food over the course of a lifetime! Now considering how significant this amount of food is, it therefore makes sense to take good care of your digestive system.

And so…

What is digestion and how does it work?

Our digestive symptom comprises an upper and a lower section. Within these two sections there are a number of certain segments, which all have their own unique, and consecutive, role in food digestion. This is how it works...

The upper digestive tract

1. Food thoughts

As soon as you think about, see or smell food, your body initiates digestion via producing and prepping digestive enzymes in anticipation of what is about to enter your mouth.

2. Food enters the mouth

Once food is placed into your mouth, the process of chewing (masticating) causes the food to physically breakdown. At this point your salivary glands release saliva which has two predominant roles. The first is to lubricate the food for ease of swallowing. The second is to initiate starch digestion via the work of one of it's enzymes 'amylase'.

3. The stomach

From the mouth, food parts are moved through the oesophagus and into the stomach. This movement of food is caused by the actions of muscles lining the digestive tract, and is known as peristalsis. Within the stomach, digestive juices (hydrochloric acid, mucus and enzymes) are released which further break the foods down, particularly proteins. The stomach muscles further get to work mixing the food and digestive juices together.

The lower digestive tract

4. The small intestine

The small intestine is where where majority of food digestion occurs. A number of very important accessory organs help this process via producing or storing secretions that eventually end up in the lumen (interior passageway) of the intestinal tract. These secretions aid digestion, as well as absorption.

The accessory organs include:

  • The Pancreas – releases digestive juice into the small intestine via small ducts. This juice contains digestive enzymes that break down carbohydrates, fats and proteins.

  • The Liver – makes a digestive juice called bile. Bile helps digest fats and some vitamins. Bile is made in the liver and delivered to the gallbladder for storage, before being released into the small intestine for use.

  • The Gallbladder – stores bile and then releases it into the small intestine when you eat.

The small intestine is made up of 3 different sections: the duodenum, jejunum and ileum. This is what happens to food once it enters your small intestine:

(i) Food moves from the stomach and into the duodenum (start of the small intestine). Here the food mixes with digestive juices, bile, and pancreatic juices.


(ii) This tropical mix (juices and bile) goes to town on all the food parts and completes the breakdown (digestion) of proteins, carbohydrates and fats into their smallest components.

Water is pulled from the circulation into the small intestine to help in the mixing and breakdown of the different food parts.


(iii) Further to this, bacteria living within the small intestine also assist the digestive process via producing enzymes that help breakdown carbohydrates.


(iv) At this point the foods have been broken down into their simplest forms… amino acids/peptides, sugars (glucose, galactose, fructose etc.), fatty acids and glycerol. As well as their vitamins and minerals released. All of these nutrients are now ready for absorption.


Now as mentioned earlier, the small intestine is made up of a number of sections, and it is at certain points along these sections that particular nutrients are absorbed. For example, iron and calcium are absorbed in the first section of the small intestine (duodenum), sugars and amino acids in the second section (jejunum) and fats in the end section (ileum).

Amino acids, sugars, glycerol, some vitamins, and minerals are absorbed across the intestinal wall and into the blood circulation.

Fatty acids and some vitamins (the fat soluble ones e.g. vitamin D) are absorbed across the intestinal wall and into the lymphatic system.

5. Large intestine

Any food parts that were not digested and absorbed in the small intestine move through to the large intestine. It is here that leftover water is absorbed back into the circulation, including with it some sodium and potassium. On top of this, bacteria living within the large intestine break some of the undigested food parts further down into their absorbable nutrient form. Furthermore, these gut bacteria use some of the undigested food parts (prebiotics) as fuel and synthesise certain nutrients, including Vitamin K and some of the B Vitamins.

Whatever is leftover, including waste products of digestion, large undigested food parts and dead bacteria, become the stool (and that’s a shit ending).

Want to learn how to eat for good gut health? Click here.