What we eat goes through quite a journey before what’s left ends up in your bathroom, but the chances are that most of won’t think digestion until something goes awry. I see an ever-increasing number of clients with digestive problems, often living with daily bloating and discomfort. Interestingly when asked to indicate where their stomach is, 8 times out of 10 they press their hands just below the navel.
If this sounds familiar, then let me take you on a quick tour of the digestive system. In this post I’ll be covering the earlier stages – saliva, chewing and then the stomach – and in the next post it’ll be the intestines, including absorption and gut bacteria.
The process of digestion doesn’t start in the mouth as one might expect, instead it starts when we see, smell or even think about food. The stimulus causes saliva to be secreted, which increases when we experience the taste. Although saliva is 99.4% water, the remaining 0.6% consists of a variety of enzymes to break down food, notably amylase that helps break down carbohydrates, as well as antibacterial agents and mucus.
We produce around 1.5litres of saliva a day, which may be decreased when dehydrated and so drinking more fluid and eating water-rich foods may help. Saliva may also be affected by both type 1 and 2 diabetes, but also many medications including those for hypertension, depression, diarrhoea, antihistamines and others that influence blood glucose levels. It is worth checking with your GP should you experience a dry mouth, and if you are taking any medication that may be implicated then the dosage may need adjusting.
Chewing is a basic yet often ignored part of digestion, as it breaks down the physical structure of food whilst exposing it to digestive enzymes. The old adage of chewing food 32 times still holds, but this is an average, as soft, water-rich food such as watermelon obviously requires less work than a piece of red meat or a handful nuts. Eating in a rush can mean that food isn’t adequately broken down into a state where there are no lumps, taking your time can help reduce gas and bloating (more of which in part 2)
Once the food is broken down into a form that is easy to swallow, known as a bolus, it travels along the throat to the esophagus and then to the stomach, via a valve, the lower esophageal sphincter. A loose valve may allow small drops of stomach acid to pass through, effectively traveling up, which can lead to reflux, or heartburn.
"Hydrochloric acid production declines with age, starting at 45 or so, which can have a knock-on effect on how efficiently you extract certain nutrients from food."
If you do experience reflux, then you should discuss this with your doctor as when left untreated there can be long term consequences. You may be prescribed a proton pump inhibitor, or PPI, which influences the cells of the stomach to produce less acid but also be advised to pay attention to what you eat.
The general advice is to avoid spicy food, acidic fruit juices, coffee, mint, late night meals, fatty foods, large meals, chocolate, alcohol and carbonated drinks. That’s quite a list, and as the evidence for each is not conclusive, and will vary from person to person, my advice is to keep a food diary and see what works for you so that you don’t have to avoid so many potentially enjoyable foods.
Once in the stomach, the bolus is now exposed to gastric juices consisting of various substances including hydrochloric acid, or Hcl, together with pepsin and protease, both digestive enzymes that work to break down protein. By the way, pepsin is produced by the same cells that make Hcl, and so PPI medication may curb protein digestion and so if reflux can be managed with diet, all the better, although you should always check with your doctor, especially if you are thinking of reducing or ceasing a prescribed medication.
Hydrochloric acid production declines with age, starting at 45 or so, which can have a knock-on effect on how efficiently you extract certain nutrients from food. The nutrients that seem to be most affected are B12, calcium, iron and beta-carotene. It should be pointed out that the decline in stomach acid, in itself, is unlikely to lead to deficiency in any of these nutrients, but even a small reduction in the amount we are able to absorb may contribute to various issues such as reduced energy and bone density.
The combined effects of saliva, chewing and gastric juices leaves what was once your lunch into a fluid made of partially digested food and liquid ready to be passed into the intestines. If food has not been broken down sufficiently it may encourage bloating and gas whilst potentially making nutrients less available for absorption.
There is a case for taking additional digestive enzymes and although most contain only modest amounts of enzymes, they can be helpful, they won’t replace chewing food thoroughly.
"additional digestive enzymes must be taken with food. Taking them too far in advance or long after eating can lead to discomfort, not unlike reflux in some cases."
There are many available, some of which contain animal-derived substances, whilst others don’t and are suitable for vegans and vegetarians. I should stress that unlike other supplements that should be taken with food, additional digestive enzymes must be taken with food. Taking them too far in advance or long after eating can lead to discomfort, not unlike reflux in some cases.
In the next post I’ll be taking a closer look at the intestines, so to speak, which will involve the confusing world of gut bacteria and probiotics.
Ian Marber’s interest in food and nutrition was piqued when diagnosed with coeliac disease in his late twenties. He soon after gave up a successful career in investment to study nutrition at the Institute for Optimum Nutrition, graduating in 1999 and founding the now-globally recognised nutritional consultancy, The Food Doctor.
Departing the Food Doctor in 2012, Ian now advises individuals and industry alike. He has since worked with over 8,000 clients, leads seminars, workshops and lectures and works closely with brands such as Innocent Drinks to formulate new ranges. His expertise has lead him to be recognised as go-to contributor within the press, writing regularly in The Times, The Spectator and The Telegraph, as well as making regular appearances on both TV and radio.