Our Digestive System

What is our digestive system?

Our digestive system, also referred to as our gastrointestinal system, consists of a number of tube-like organs that start at the mouth and end at the anus. There is approximately nine meters of these connected tube-like organs inside each of us. It includes our mouth, throat, oesophagus, stomach, small intestine, large intestine, rectum, anus, pancreas, liver and gallbladder.

Our digestive system also includes approximately 100 trillion microorganisms that live in our gastrointestinal tract, known as gut microbiota or gut flora. These microbiota provide health benefits to us as their host and also support healthy digestion.

What is the role of our digestive system?

Our digestive system is responsible for converting the food and liquids we consume into energy and eliminating the indigestible components as waste products. It allows food to be broken down into nutrients, vitamins and minerals so they can be absorbed in the bloodstream and used by the body for energy, growth and repair. Carbohydrates are broken down into simple sugars glucose, fructose and sucrose, proteins are broken down into amino acids and fats are broken down into fatty acids and glycerol.

Our microbiota also have an important role in strengthening gut integrity, energy production and immune protection.

How does digestion work?

Digestion is controlled by hormones and nerves that allow your brain and gastrointestinal tract to communicate. Digestion starts in the mouth where food is chewed, grinded and combined with saliva and enzymes to become a small round bolus for swallowing. The bolus is then transported down the throat to the oesophagus. Muscular contractions known as peristalsis then transport the bolus to the stomach. The stomach combines digestive juices with the bolus to breakdown proteins and fats. The stomach also secretes hydrochloric acid to help dissolve the bolus and eliminate any harmful bacteria. The stomach then slowly releases the end product called chime into the small intestines.

The small intestine is the primary site for the digestion and absorption of nutrients. It is responsible for transporting nutrients into the bloodstream and to the liver. Then the remaining food mass passes in to the large intestine. In the large intestine billions of harmless microorganisms feed on the remaining food mass. Dead cells are excreted, and any remaining water is reabsorbed to form a more solid mass known as the stool. Peristalsis then moves the stool from the large intestines to the rectum where it stays until it is excreted from the anus.

The liver, gallbladder and pancreas also have an important role in digestion. The pancreas produces digestive enzymes that are pumped into the small intestine and the gallbladder releases bile for dissolving fats. The liver detoxifies nutrient-rich blood transported from the gut and further processes nutrients, so they can be used by the body.

We don’t often consider the significant amount of work performed by our digestive system as it is mostly an involuntary process. However, while we are busy getting through our day our digestive system is working hard to help us feel our best. 

Structure of the digestive system

Our digestive system is made up of the gastrointestinal tract, a number of hollow organs that start at the mouth and finish at the anus. Each organ in the gastrointestinal tract has an important role in the maintenance of digestive health and our overall health and wellbeing.

The gastrointestinal tract organs include the:

  • Mouth: Digestion begins in the mouth where food is broken down through chewing and saliva making it possible for the body to use.
  • Throat: The throat transports food from the mouth to the oesophagus and prevents food from travelling up the nose or down our windpipe towards the lungs.
  • Oesophagus: The oesophagus receives food from the mouth and produces muscular contractions known as peristalsis to allow the food to be moved to the stomach.
  • Stomach: The stomach is responsible for storing food. It also uses hydrochloric acid and enzymes to breakdown food into smaller pieces for easier digestion.
  • Small intestine: In the small intestine the food mass is diluted with enzymes and bile to form a more liquid mass. It is also the primary site for the absorption of fats and nutrients.
  • Large intestine: The large intestine absorbs water from the food mass to form a solid mass. It is also home to a number of bacteria that can support digestion and are essential for healthy intestinal function.
  • Rectum and anus: These organs signal the waste products of digestion to be excreted from the body as a stool. 

The digestive system also includes several organs outside of the gastrointestinal tract that help facilitate digestion. These organs are housed in the abdominal cavity that is behind our abdominal wall and in front of our spine. They include the:

  • Pancreas: The pancreas produces the digestive enzymes including amylase for carbohydrate digestion, lipase for fat digestion and trypsin for protein digestion.
  • Liver: The liver detoxifies nutrient-rich blood transported from the gut and further breaks down nutrients so they can be used by the body. The liver also produces bile that is essential for digestion.
  • Gallbladder: The gallbladder stores bile and is responsible for the release of bile into the small intestines.

As digestion is an involuntary process it is easy to forget how much work our digestive system is responsible for. Yet there is plenty of reason to appreciate these organs that make up our digestive system as they are essential for healthy digestion, nutrient production, immune system function and brain function.

Read on to see how our diet affects our digestive health...

The role of diet on our digestive health

The old saying “we are what we eat” has never been more relevant with evidence showing that our diet plays an important role in our digestive health. What we choose to put into our mouths can impact digestive function and the approximately 100 trillion microorganisms that reside in our digestive tract. These microorganisms called gut microbiota have an important role in our body affecting digestion, inflammation and immune health.

It is understood that poor dietary habits can impact the number and diversity of microbiota populations causing dysbiosis. Dysbiosis is where there is an overgrowth of unfavourable gut microbiota species. Dysbiosis has been associated with compromised digestive well-being.

For those of us looking to improve our dietary intake it is reassuring to know that by making healthy dietary choices you can rapidly alter your microbiota for improved digestive health.

Some dietary sources to include in your diet that have been shown to support healthy microbiota and digestive health include:


Consuming adequate dietary fibre is necessary for digestive health particularly the well-being of the large bowel. The National Health and Medical Research Council recommend that women consume 25g of fibre daily and men consume 30g daily. Some of the best food sources high in dietary fibre include whole grain breads and cereals, vegetables, legumes and fruit.

The soluble fibre found in vegetables, fruits, oats and legumes helps to slow the emptying process of our stomachs. This enables us to feel fuller for longer and maintain blood sugar levels.

The insoluble fibre found in nuts, seeds and the skins of fruit and vegetables helps to ensure satiety and maintain a healthy bowel environment. Insoluble fibre supports regular bowel motions through absorbing water to help soften the large intestine contents.

Resistant starch found in cooked and cooled potato and under-ripe bananas is not digested in the small intestine and is transported to the large intestine. Here it is able to support bowel health and assist the production of beneficial microbiota.


Protein when combined with carbohydrates in the large bowel can contribute to digestive health. Protein is a dietary source of nitrogen that the microbiota in the colon need for growth, the breaking down of carbohydrates and also the production of short-chain fatty acids (SCFA). We need SCFAs as an energy source for our microbiota and tissues as well as to maintain healthy tissue integrity.


Prebiotics are non-digestible food components that can alter the microbiota living in our digestive tract to offer us health benefits. Prebiotics have the potential to boost digestive health, support the immune system and improve mineral absorption

Aim to include at least 5g of prebiotics in your diet each day for digestive health. Foods that are a good dietary source of prebiotics include onion, Jerusalem artichokes, chicory root, garlic and bananas, however you would need to consume large amounts of each to reach the recommended amount. To ensure you receive the beneficial quantity of prebiotics you could consider using a prebiotic supplement to help boost your digestive health.


A probiotic is a live organism that when consumed can provide benefits to the host. Probiotics can help aid digestion, produce vitamins, assist nutrient absorption, support healthy immune function and discourage the overgrowth of harmful microorganisms.

Probiotics are a source of live bacteria that introduce and establish good bacteria in our gut, while the above-mentioned prebiotics help to nourish and support our good bacteria.

There are a number of probiotics consumed for their health benefits with some of the most common species being Lactobacillus and Bifidobacterium. Common dietary sources of probiotics include yoghurt and fermented foods such as kimchi, sauerkraut, kefir and kombucha. Probiotics are also available in supplement form and usually have a higher number of probiotics compared to food sources.

Scientific studies have shown the benefit of some particular probiotics for individual digestive conditions,. However, to use probiotics for these specific digestive issues it is important to use each probiotic strain at an adequate amount scientifically shown to support the condition, as not all types of probiotics have the same effect in the body.


Adequate water is essential for healthy digestive function as low water intake can reduce the water content of stools and contribute to constipation. Ensure that you consume the recommended 3.4L of water daily for men and 2.8L of water daily for women from foods and fluids. You may require greater quantities of water if you are exercising frequently, living in a warm environment or consuming caffeine.

There are also some food elements that can impair digestive function and should be limited in the diet for optimal digestive health. These include:

Unhealthy fats

Unhealthy dietary fats such as trans-saturated fats have been shown to alter the composition of gut microbiota. Diets that are high in these unhealthy fats increase lipopolysaccharide (LPS). LPS is found on the outer cell wall of gram-negative bacteria and can affect tissue inflammation and immune responses.


Too much alcohol may also compromise gut health.

If including alcohol in your diet you should follow the National Health and Medical Research Council’s guidelines of no more than two standard drinks on any day.

Here we’ve looked at some elements that may affect digestive health. Perhaps you would like to know more about the signs and symptoms of poor digestive health...

Signs and symptoms of poor digestion

Digestive complaints are commonly experienced and on the rise with 50% of people complaining of a digestive problem over any 12 month period.

Healthy digestive function is essential for food absorption, stabilising your gut microbiota, maintaining immune function and allowing you to feel your best.

There are a number of common digestive signs and symptoms that may indicate impaired digestive function including:


Constipation is a hard, or infrequent, or difficult or incomplete bowel motion. Almost one in five people over the age of 30 have experienced constipation. Some of the common symptoms of constipation can include hard stools, the feeling of not completely emptying the bowel, abdominal bloating, straining when having a bowel motion and infrequent bowel motions.

When diagnosing an individual’s constipation, it is important to note that each individual’s normal bowel function can vary. Healthy bowel function can range from passing one to three stools a day to passing a stool every three to four days. Identifying any changes in the frequency, size and consistency of your stool compared to what you would consider normal is important to consider when diagnosing constipation.

Constipation is most commonly caused by the consumption of a low-fibre diet, inadequate fluid intake, medications and drugs that alter bowel function, and the consumption of constipating foods such as rice, bread, bananas, meat, poultry and fish.

While constipation is a common condition it doesn’t need to be tolerated as it may have long-term health implications. Constipation can be managed and modified with regular exercise, eating a high fibre diet and consuming adequate water.


Diarrhoea is an increase in the frequency, volume or liquid consistency of a stool for an individual. It can be accompanied by urgency to have a bowel motion, cramping, gas, vomiting and/or nausea.

Diarrhoea occurs when insufficient water is removed from the stool during digestion so it becomes loose and poorly formed. This can occur when the stool passes too quickly through the digestive tract, contains excess water secreted by the intestines or contains substances that prevents water absorption in the large intestine.

Dehydration can often coincide with diarrhoea due to excessive fluid being excreted.

Diarrhoea lasting less than a week is most commonly caused by an infection from bacteria, virus or parasite, food poisoning, stress, anxiety or a medication side effect. Diarrhoea lasting for longer than four weeks may indicate something more serious and the advice of a healthcare professional should be sought.

Some foods can also cause diarrhoea when particular food substances cannot be absorbed through the colon wall and remain in the intestine causing excessive water to remain in the stool. Some of the most common food intolerances that can cause diarrhoea include fruits, beans, dairy products containing lactase and packaged foods containing sorbitol and mannitol.

Diarrhoea can lead to a loss of key electrolytes including sodium, potassium, magnesium, chloride and bicarbonate. It can also cause nutritional deficiencies, weakness, fainting and should not be endured long-term.


Bloating is the feeling of distention or swelling of the abdomen that can be uncomfortable and painful. It is common for bloating to increase as the day progresses and can sometimes cause clothing to become tight and uncomfortable.

Around 10-25% of people commonly experience bloating symptoms. Bloating frequently occurs alongside bowel discomfort and constipation.

While the exact cause of bloating isn’t well understood it is known that some drugs and medications, as well as digestive disorders such as poor stomach emptying may contribute.

A number of foods can also cause bloating in some individuals. Some of the most common foods that can cause bloating include onion, garlic, wheat, rye, stone fruit and lactose products such as cow’s milk.


Reflux occurs in about 10-20% of adults and frequently in infants. It is when there is impaired functioning of the lower oesophageal sphincter muscle that allows the contents of the stomach to flow back into the oesophagus. This can be spontaneous and involuntary and result in oesophageal inflammation and irritation, pain felt in the lower chest and heartburn. Additional symptoms of reflux can include regurgitation, the sensation of having a lump in the throat, cough, wheezing and difficulty swallowing.

Various factors have been associated with exacerbating GORD such as pregnancy, high fat foods, consumption of a large meal, caffeine, carbonated beverages, alcohol, smoking and some medications.


Heartburn is a painful burning sensation felt in the chest behind the breastbone. It is a commonly experienced symptom with seven in ten Australians suffering from heartburn at some stage in their life. A bitter or sour taste in the mouth may accompany heartburn when the acidity of the stomach contents flows upwards.

Heartburn can be exacerbated by the consumption of a large meal, lying down immediately after eating and pregnancy.


Indigestion is where discomfort and pain is felt in the upper abdomen and symptoms may include fullness, burning or gassiness. Indigestion can often be accompanied by additional symptoms such as nausea, poor appetite, diarrhoea, constipation, flatulence and burping.

Sudden indigestion can be caused by excessive food consumption, alcohol or medications, whereas recurrent indigestion may be caused by delayed stomach emptying or may indicate more serious conditions


Flatulence is gas produced by bacteria in the large intestine that is expelled through the anus and is commonly referred to as passing wind. The gasses expelled are most commonly hydrogen, methane and carbon dioxide gases and they may or may not have an odour. It is normal to pass wind 2-30 times a day. This equals between half to one and a half litres of gas daily, although this may vary for each individual. Men report passing wind an average of 12 times a day compared to seven times a day for women. When an individual passes more gas than what they would normally produce it is considered excessive flatus. This excessive gas can be caused by impaired absorption in the digestive tract known as malabsorption and may result in inadequate nutrient absorption.

Excessive gas can also be caused by the consumption of certain foods. Common gas producing foods include those with poorly digestible carbohydrates and fats, such as those high in dietary fibre like baked beans and cabbage, foods with sugars such as fructose and foods with sugar alcohols like sorbitol.


Belching, commonly referred to as burping, is the expulsion of air from the digestive tract out the mouth. It usually occurs shortly after the consumption of a meal but can also occur when you are feeling stressed.

Belching is caused by the consumption of air while eating or drinking or from gas created through the consumption of carbonated drinks. It can also be caused by excessive air consumption during smoking, stressful periods, or excessive salivation.

Food intolerances

A food intolerance is a non-immunoglobin E (IgE) mediated food sensitivity and refers to a difficulty in digesting specific foods. A non-IgE mediated reaction means it does not trigger the immune system and is different from a food allergy that does trigger the release of IgE.

Food intolerance symptoms can include bloating, headaches, abdominal pain, rash, mouth ulcers, cough, runny nose and an irritable bowel. The symptoms of a food intolerance usually occur within 2-48 hours after ingesting the trigger food and may continue for several hours to a number of days.

Some of the most common food intolerances are to monosodium glutamate (MSG), gluten, dairy, beans and legumes. There are also some naturally occurring chemicals in food that have been associated with food intolerances including salicylates, histamines and amines. Salicylates are plant chemicals found in herbs, spices, fruits and vegetables. Histamines are chemicals that are produced in an allergic response and are found in pickled vegetables, sauerkraut, aged cheeses, smoked meats, chocolate and nuts. Amines are formed by the breakdown of protein or the fermentation of foods and are found in chocolate, red wine, aged cheese, avocado, citrus fruits and baked meats.


Vomiting is where a forceful contraction of the stomach that causes its contents to be expelled out the mouth. It can often be uncomfortable and violent and can be accompanied by nausea.

Vomiting can occur with any digestive tract dysfunction and some of the most common causes include digestive tract infections, medications, drugs, alcohol and toxins.


Nausea is the feeling of needing to vomit and can often be uncomfortable and unpleasant. Nausea can be accompanied by mouth watering, loss of appetite, abdominal discomfort and dizziness.

Pain and cramping

Abdominal pain is pain or cramping that is felt in your lower or upper abdominal area. It is also often referred to as stomach pain. Stomach pain is common with 30% of Australians suffering stomach aches and cramps every few months or more.

Common causes of abdominal pain include constipation, food intolerances, indigestion, and medications. Abdominal pain can also be experienced due to more serious conditions so if abdominal pain persists for three months or more, is severe or is associated with weight loss, bleeding from the bowel, difficulty swallowing or persistent vomiting you should consult your healthcare practitioner.

Bad breath

Bad breath, medically recognised as halitosis is an unfavourable smell from the mouth. Odourous substances are present when air is exhaled, such as volatile sulphur compounds produced by bacteria. It is understood that halitosis affects 25-30% of the world’s population.

Bad breath is most commonly caused by poor dental hygiene, bacterial coating of the tongue, gum conditions and different foods. Other causes of bad breath can include poor diet, alcohol abuse and smoking.

Anal itching

Anal itching is an itch at the end of the digestive tract where the stool is evacuated from the body, known as the anus. Anal itching can also occur at the skin surrounding the anus known as the perianal skin.

Anal itching can be caused by medications, skin irritants, poor hygiene habits, bacterial or yeast infections or skin conditions like dermatitis and psoriasis. Anal itching can also be triggered by certain foods such as chocolate, caffeine, beer, milk products, chilli, nuts, tomato products, spices and citrus.

When to seek help

If you are experiencing any of these digestive signs or symptoms on an ongoing basis it is recommended that you speak to your healthcare practitioner. It also may be worth noting any digestive changes as this may highlight impaired digestion. Keeping a diary with your symptoms and any potential triggers such as food, stress, medication, alcohol, tobacco or toxins may help to identify the underlying cause.


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