‘A taste on the lips, forever on the hips’ goes the saying and, of course, if we are talking about CARBS and other sugars then that is extremely apt. But what we need to develop is a heightened awareness of what happens once food has left our mouth. It’s amazing that the vast majority of humans (including me for 48 years) eat stuff every day and only ever think about how it tastes. Most people only ever think about the very first step of the process, because it’s the only step that they misguidedly believe they actually experience. The reality of course is very different.

Let’s first look at how we digest food. The act of digestion is the breaking down of food by a combination of chemical and physical means. If we can understand the basics, then we will begin to understand how important it is that we eat the right things. When we talk about digestion, it all starts in our nostrils. We rev up our digestive machine the moment we smell the aromas from food. Whether it is sweets, Sunday dinner or a ripe fruit, our mouths begin to produce saliva, our bellies rumble and our intestinal glands set in motion the secretion of various chemicals. Our eyes can also kickstart our digestive system by sending positive messages to the brain.

Then, as we chew our food, our teeth and tongue work in partnership with saliva
to break it down for delivery into our body. The mush then travels down from our throat into a 25cm long tube called the oesophagus (also called the gastro-intestinal tract or GI tract) and drops into our stomach. It might surprise you that food doesn’t just sit still in our stomach, but is churned like a washing machine, with its contents constantly hitting the sidewalls until they break down into much smaller particles. The physical motion is aided by enzymes (molecules that speed up chemical reactions) and acids that are strong enough to dissolve some metals. The length of the stomach spin cycle varies depending on what we have eaten. Simple CARBS virtually pass straight through, but more fibrous foods and meats can take five or six hours before they are ready to leave the stomach on their way to the small intestine.

Our small intestine is a massive 7m (23 feet) in length, and it is way more complex than we might at first imagine. On the inside its surface is not smooth, but looks like a valley full of billions of little cactus plants. These enable the small intestine to create a huge surface area that is bigger than a tennis court! Each square millimetre of our small intestine is filled with 30 or so of these cactus-like structures known as villi. But what purpose does our small intestine fulfil? It breaks down all of the food we eat into the three macronutrients: fat into fatty acids, carbohydrates into sugar and protein into amino acids. The villi then absorb these molecules, placing the sugar and amino acids into our bloodstream, and dispatching them to the liver to perform a safety check before being passed into the main circulatory system.

The small intestine has to process fat differently. Fat is insoluble and therefore can’t be dispatched into the bloodstream. Instead the small intestine sends fats (along with insoluble vitamins A, D, E and K) on a different highway known as the lymphatic system. This works alongside the blood vessels that carry protein and CARBS (sugars). It’s like a dual carriageway running alongside the motorways of the body.

Although the two run alongside each another, there is one major difference. While
the liver performs a safety check on the sugar and amino acids in our blood before allowing it into the stream, the lymphatic system does not pass its produce through any organ for a safety check. This is one of the reasons why it is important to understand the difference between healthy and unhealthy fats. The fats go straight to the heart to be pumped out into our system. The heart can’t perform any detoxification process like the liver does – it can’t tell the difference between healthy coconut oil or the deadly highly processed so-called vegetable oils found in packaged food - it just simply injects it into our bloodstream.

If you try to picture the small intestine, you might think that, with its complex cactus - like lining and its job of making all different types of food - from curries to cakes - disappear, it is a pretty smelly and dirty environment. However, at the end of each process, it actually goes through its own cleaning and cleansing routine. The problem is that, if we constantly eat food, it never gets time to finish the job properly. This is one of the many benefits of intermittent fasting – it lets our small intestine finish its cleaning routine properly.

Let’s recap on the function of the small intestine (also known as the small bowel).
It acts like a giant cheese grater and breaks down food into the three main macronutrients and dispatches the energy to fuel our body. Picture it as our internal food processor – it’s quick and efficient, and with some types of food gets straight to work after we have eaten. But not everything we consume can be digested by the small intestine, and what it can’t cope with is passed into the large intestine.

happy gut

The large intestine is our wellbeing centre. Its job is to process all the micronutrients and vitamins that our body requires to operate correctly. It is slower and more precise and sifts through all the leftovers passed on by the small intestine. In terms of length, our large intestine is approximately 1.5 metres long (far shorter than the small intestine) but receives its ‘large’ prefix because of its diameter, which is a gigantic 6 to 7cm (2.3 to 2.8in). Yes, we have a pipe inside us that’s as long as a pogo stick and as wide as a drainpipe. When we stop and think about how massive these two organs are, our first impression might be to question the reason for their vast size. After all, their role doesn’t sound as vital as the lungs that keep us breathing or the heart that pumps blood around our body – both of which are tiny by comparison. But their vast size should act as proof of how vital what we eat is to our overall wellbeing.

Let’s get back to the role of our large intestine. Its job is to deal with all of the undigested stuff, and it does this in several ways. Firstly, it tries to reclaim all of the fluids that have been used in the digestive process and put them back into the body. The part of the large intestine responsible for returning water and salts is known as the colon. Another vital role for the large intestine is to process nutrients. It is also home to huge colonies of microbes known as our gut flora, which believe it or not weighs more than our brain. Yes, you read that right, the bacteria in our intestine weighs more than our brain! So maybe it stands to reason that our gut control far more of our health and wellbeing than we realise.

Once the entire digestive tract has finished its job, the large intestine signals to the brain that it’s home time, and together they converse with both the final part of the large intestine, the rectum, and our circadian body clock on the exit strategy for the leftovers, i.e. faeces! The whole procedure of processing food varies in length based on several things, including what we have eaten, our age, stress levels and exercise. On average, assume it’s a 16 to 24-hour cycle.