With the festive season in full swing, spare a thought for your gut. There is more to it than you might think. In fact, it is a part of us that it is easy to ignore, as it tends to get on with the job in hand without us even being aware of it.
You may be surprised to learn that the gut’s network of nerves is as large and complex as the brain, which is why it is called the ‘gut brain’. We can even feel emotions in our gut, hence phrases like ‘gut feeling’ and ‘butterflies in the stomach’. A healthy gut can promote a general sense a wellbeing and an irritated gut can cause anxiety and depression. Serotonin is a hormone that makes us feel good and “95% of the serotonin we produce is manufactured in the cells of the gut, where it has an enormous effect on enabling the nerves to stimulate muscle movement, and acts as an important signaling molecule” [Giulia Enders/Gut].
As you can see, the gut does more than just digest food. That said, digestion is its main job and it does that in four stages - in the mouth, stomach, small intestine and large intestine.
The mouth has several roles in the digestive process: ingestion (taking in food and drink), the mechanical breakdown of food through chewing, starting the chemical breakdown of starch and swallowing.
Saliva is an important factor in this, with the salivary glands releasing about 1 litre of saliva into the mouth each day. Saliva is effectively filtered blood and does many things: it lubricates the mouth for talking and chewing, it contains the starch-digesting enzyme amylase and it helps keep the mouth and teeth clean, protecting against bacterial infection. There are more nerve endings in the mouth than almost anywhere else in the body, so saliva also contains a natural pain killer opiorphin, which is stronger than morphine, but released in very small quantities to numb most minor damage to the mouth from food and teeth.
Chewing food properly is important to help mix it with saliva and to break it down as much as possible before the rest of the digestive process gets to work on it. As a colleague used to point out to her children 'You don't have teeth in your stomach, so use them where you can!'
Food passes from the mouth to the stomach along a muscular tube: the oesophagus. The stomach is a lopsided J shape, starting below the left nipple and ending just below the right-hand-side of the rib cage, so when we have pain lower down in the abdomen, it isn’t really 'stomach' ache. This position is also why the pain of reflux (the back flow of stomach acid into the oesophagus) can feel like it is from the heart, hence the term ‘heartburn’.
The main functions of the stomach are to mix food with gastric juices and to start the digestive process on proteins. The stomach will hold onto meat for up to six hours, digesting the proteins and fat, but it passes carbohydrate-rich foods quickly onto the small intestines. Cooking starts the breakdown process of proteins and so saves our digestive system time, energy and resources, which is why we like cooked food. The acidity of the stomach helps protect against infection from any contaminated food that we may have eaten.
Stress can affect the ability of the smooth muscle of the stomach to stretch, which is why we can lose our appetite or feel sick under extreme pressure.
The small intestine (all 7 metres of it) completes the chemical breakdown of food and is where most nutrient absorption occurs. Once that job is done, it cleans itself, which is the rumbling sound that we mistakenly think is from an empty stomach. The cleaning process in the small intestine will stop if more food is consumed before it has been completed, which is why it is healthy to avoid snacking and to leave a gap of a few hours between meals.
We can feel tired after a meal because although our stomach feels full, we haven’t yet absorbed the nutrients from it. Also, the process of digesting a meal requires extra blood to be diverted to the digestive system, so there may be less available for the brain and the rest of the body (bear that in mind after your Christmas meal and enjoy succumbing to it). Whereas resting after a meal can help optimize the digestive process, stress can inhibit it by redirecting blood to the brain and muscles. That is why chronic stress can lead to digestive disorders.
What is left of the food passes from the small intestine into the large intestine where water and any remaining nutrients are absorbed over a period of about 16 hours. The large intestine is about 1.5 metres in length and moves much less than the small intestine. Fibre in the diet is important as it stimulates the peristaltic motion of the intestines and so aids digestion.
The other function of the large intestine is excretion of waste. If at the end of the digestive process you have difficulty passing the final product, try putting your feet on a low footrest while sitting on the toilet; it mimics the natural squatting posture. Adopting a squatting position can also prevent haemorrhoids and diverticulosis as it reduces the pressure on this part of the digestive tract.
Other ways of avoiding constipation are to ensure that you consume enough dietary fibre from plant foods and to keep yourself hydrated. Our gut is a creature of habit, which is why travel can upset our usual bowel habit, but it usually resumes within a day or two, so don't panic if that happens to you!
On that note, I will end. I hope this post has helped you appreciate the amazing job that your gut will be doing over the next few days of feasting! If you are interested in learning more about the gut, I can highly recommend Giulia Enders’ book Gut: the inside story of our body’s most under-rated organ. And if you would like to treat your gut (and the rest of you) to some rest and relaxation, do get in touch to book a massage.