It might seem obvious and straight-forward, but digestion is one of the most basic foundations of good health. This incredible process, through which our body extracts nutrients from food, is responsible for sustaining our very survival. Digestion is a series of complex and interdependent chemical reactions that together break down food into molecules that will nourish us at a cellular level.

In this 3 part series we look at the 4 stages of digestion and how even the slightest imbalance can have negative cascade of impacts on the rest of your body.

Having a proper understanding of how digestion works is a critical foundation for looking after your health without a host of drugs and medication.


Every cell that makes up every tissue, that makes up every organ, depends on the body’s digestive system to provide the nutrients it needs to function.

Stage one: Brain, mouth and oesophagus

Digestion is a north to south process that really starts in the brain. When we see or smell food, the brain registers this and sends a signal to the rest of the digestive system to prepare. We will start to salivate, as the brain tells the salivary glands to produce salvia.

The mouth acts as the physical gateway to the rest of the digestive system. Both mechanical and chemical digestive actions occur here. Our teeth and jaw perform the mechanical function as we chew food into small pieces. The salivary glands complete the chemical function as they secrete saliva, which moistens food and facilitates swallowing.

Digestion of carbohydrates begins in the mouth as the digestive enzyme salivary amylase is produced. As carbohydrates are broken down, the molecules become simple sugars. This is why foods like bread, broccoli and carrots will start to taste slightly sweet if you chew them well enough. As regular A No Grainer readers will know, everything that isn’t protein or fat is a carb and this digestion occurs first.

Chewing is a critical part of digestion that many of us do not do well. With our busy lives it is sometimes hard to find time to eat, let alone to sit down to a quality meal and eat it slowly and with thought. However, to facilitate a healthy downstream digestive process, chewing is absolutely crucial.

We can all make small changes that will have profound impacts on our health – chewing food sufficiently is one of them.

The brain, mouth and oesophagus are responsible for the first stage of digestion.

When we swallow food it passes through the oesophagus, which is the hollow tube between the mouth and stomach. The cells that line the oesophagus initiate a series of contractions (peristalsis) to propel food into stomach. At the top end of the stomach is the lower oesophageal sphincter (LOS), which open up to allow the chewed food contents through. After swallowing the LOS pressure drops and remains low for about 6-8 seconds to allow food to pass through. Stomach contractions then increase pressure and LOS tightens again.

In healthy digestion the LOS remains closed unless it is letting food pass through to the stomach, or in the rare instance we need to quickly expel the contents of the stomach (due to a pathogen or bug) when we vomit. When the LOS becomes weak and stomach contents is able to escape, then we experience the symptoms of heart burn.

In part II of this series on digestion we look at the stomach. 

I cover heartburn and the real reason we experience it in great detail in this article.



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