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A guide to
nutrition


What are
functional foods?

Probiotics &
your health

Obesity –
an Irish epidemic

Nutrition & pregnancy

Your digestive system

The role of vitamins & minerals

Finland – a case
study in healthy
eating


Health Calculators

 


What is the gut?
What role does saliva play in digestion?
How does the stomach work?
What is the small intestine?
How does digestion occur in the small intestine?
What role does the large intestine play in digestion?
What are the more common problems associated with the digestive system?

What is the gut?
Your gut is a muscular tube about seven metres long, which breaks down food for use in the body. Digestion, or the breaking down of food, begins the moment you start to chew your food, when saliva (or spit) comes in contact with it.


What role does saliva play in digestion?

Saliva is secreted by glands in the mouth and is mixed with food as you chew. Certain nutrients, known as carbohydrates, are a more complex form of sugar and begin to be broken down by saliva in the mouth.

When you swallow the food, it passes down a pipe known as your oesophagus (or gullet) from where it passes into your stomach. Part of the gut wall is made of muscle and this contracts in a wave-like motion, helping the food to move further down the intestines.


How does the stomach work?
The stomach is a small, pear shaped, hollow, muscular organ about the size of a clenched fist. Where the gullet joins the stomach, a ring of muscle (or sphincter) acts like a valve, allowing food to pass through and keeping it in the stomach while it is being digested. A similar valve at the other end of the stomach keeps the food there until it is ready to pass on to the next part of the gut, the small bowel.

The stomach secretes juices from glands in its walls which contain chemicals that break down the food further. One of these chemicals, protease breaks down one type of food, protein, while another, hydrochloric acid, destroys any bacteria present in food and provides an acidic environment within which the protease best works.

Once the stomach has partially digested the food, it acts as a reservoir for the food, which, at this stage, is semi-liquid. The stomach releases this through the lower sphincter, into the small bowel (or small intestine), the next part of the gut.


What is the small intestine?
The small intestine is part of the gut. It is roughly two to four centimetres in diameter, earning its name because it is narrower than the large intestine, which is about six centimetres in diameter. However, despite its name, the small intestine is the longest part of the gut and can be five or six metres long.

The small intestine is divided into three parts – the duodenum, the part nearest the stomach; the jejunum, which follows this; and the ileum, which is the part of the small intestine that joins with the large intestine.


How does digestion occur in the small intestine?
Because the food entering your duodenum from the stomach is so acidic, alkaline juices are secreted in the duodenum to neutralise it. These digestive juices continue to digest the food further and are released by an organ known as the pancreas, which is located near the liver. Bile is also secreted by the gall bladder (a small sac underneath the liver which stores the bile made by the liver). Bile breaks down fatty foods.

Food consists of three main nutrients, protein, carbohydrates and fats, which must be digested or broken down in order to allow our bodies to use them. As protein-rich food is digested it is broken down into amino acids, carbohydrates are broken down into glucose and other simple sugars and fat is broken down into fatty acids and glycerol.

As the broken down parts of the food pass down in to the jejunum and ileum they are absorbed through the gut wall and into the bloodstream. The lining of the gut at this point is covered with tiny, finger-like projections which help to absorb the broken down elements of the food.


What role does the large intestine play in digestion?
Once the useful parts have been absorbed, the rest of the undigested food passes further on down the gut, into what is called the large intestine. The large intestine is about one metre long and it is made up of the colon, the rectum and the anus. Its main job is to reabsorb water from the undigested food and to eliminate the parts of the food that are indigestible, such as fibre.

When the water is reabsorbed, what remains is known as faeces, which passes along the rest of the large intestine and are passed through the rectum and out of the body via the anus.


What are the more common problems associated with the digestive system?
Piles/haemorrhoids
Haemorrhoids are small, swollen veins around the rectum or anus. They may occur in the anal canal or at the anal opening and they can lead to anal bleeding, itching and discomfort.


Piles can be caused by constipation and straining during bowel movements, as can a low fibre diet, prolonged sitting or standing, obesity, anal intercourse and pregnancy.
A high fibre diet with more green vegetables, fresh fruit, wholegrain cereals and bran is recommended. People with piles should drink eight to 10 glasses of water every day and exercise regularly.

Constipation
Constipation is the infrequent and difficult passage of stool, the waste products produced following the digestion of the food we eat. The stool may be too hard, infrequent, small or difficult to expel.

In some people, constipation is sudden and often a symptom of another problem in the gut, such as bowel obstruction, where the food and faeces cannot pass through it. The incidence of constipation increases with age, and is most common after 60. A change in bowel habit (without change in diet) is a significant symptom which should be brought to the attention of your doctor.

Constipation may be caused by various medications such as general anaesthesia or iron, analgesics, tranquillisers and sedatives.

Other causes include a diet low in fibre content, colon cancer, irritable bowel syndrome and colonic diverticulosis. The treatment consists of a high-fibre diet, plenty of liquids and exercise.

Reflux/oesophagitis/heartburn/GORD
The escape of the acid is known as reflux and it irritates the lining of the oesophagus, causing inflammation, known as oesophagitis or heartburn. The chronic condition is known as GORD – gastro-oesophageal reflux disorder.

Peptic ulcer
A peptic ulcer occurs when the lining of the gullet (oesophagus), stomach or the duodenum (part of the small bowel) becomes corroded by stomach acid. Such an ulcer in the gullet is called an oesophageal ulcer, a stomach is called a gastric ulcer and a duodenal ulcer occurs in the duodenum.

Most peptic ulcers are caused by a bacteria called Helicobacter pylori or H pylori which is able to withstand the destructive effects of the stomach secretions. Some medications can cause ulcers and for this reason, we are often told to take them with food, in order to prevent the development of an ulcer. These medications include aspirin and certain other prescription drugs, including non-steroidal anti-inflammatories (NSAIDs). These drugs are commonly prescribed for arthritis and rheumatism.

Some rare conditions can also cause peptic ulcers, including Crohn’s disease (see below) and Zollinger-Ellison syndrome. A number of treatments for peptic ulcers are available but in nutritional terms, avoiding alcohol can help, as can limiting the intake of spicy foods, caffeine and very hot liquids.

Irritable bowel syndrome
Irritable bowel syndrome (IBS) is a spasm of the bowel wall due to mild stimulation when eating, when wind develops or due to the presence of stool in the bowel.

Irritable bowel syndrome, which is also known as spastic colon, causes abdominal pain, bloating and irregular bowel habits, such as alternating diarrhoea and constipation. It is thought to be due to abnormal contractions of the large intestine. Dietary factors may also play a role.

Symptoms include explosive diarrhoea, constipation or an alternating combination of both. Excessive wind, a bloated feeling, belching and flatulence may also feature. Stool may be small and mucous, and abdominal pain can be quite severe. Occasionally people with IBS experience heartburn, nausea and vomiting.

Treatment of the problem depends on the symptoms experienced but a high-fibre diet and exclusion of foods that cause the problem is usually recommended.

Flatulence
Excessive flatulence (farting) can occur for many reasons, including smoking, lactose intolerance, certain foods, swallowing too much air and too much bacteria in the colon.

Eating slowly and chewing food for longer allows the enzymes in saliva to begin to digest the food before it enters the stomach. Swallowed air is a prime cause of flatulence and careful chewing helps to avoid swallowing air that can occur when food is eaten too quickly. Excessive flatulence may be a symptom of appendicitis, gallstones, stomach ulcers or irritable bowel syndrome.

Coeliac disease
The exact cause of coeliac disease is unknown, but there is possibly a genetic factor and it is very common in the Irish population. Coeliac disease is a reaction by certain cells in the gut to gluten, a protein found in wheat or related grains, such as rye, barley and oats,
which gives to the dough its tough, elastic consistency.

Normally these cells protect the body against invading organisms, but in coeliac disease the gluten is attacked by mistake. As a result, the small intestine becomes inflamed and has difficulty properly absorbing nutrients from food.

Symptoms include diarrhoea, chronic fatigue, constipation, weight loss due to the malabsorption of nutrients, anaemia due to the poor absorption of iron, amongst other problems.

The only foods that present a problem for a person with coeliac disease are those containing gluten, therefore treatment involves the complete avoidance of gluten in the diet. In most cases, this can lead to healing of the small intestine. A gluten free diet still allows the person to enjoy a very wide range of foods including meat, chicken, fish, fruit, vegetables and dairy products.

Breastfeeding babies is recommended if at all possible as it delays the introduction of food containing gluten to babies, thus making them less likely to develop the disease.

Diverticulitis
Lack of fibre in the diet can cause diverticular disease or diverticulitis. This is the inflammation of the small pouches or diverticula that occur abnormally on the wall of the large intestine or colon.

Most people who develop diverticulitis have previously experienced constipation. The increased pressure on the bowel which occurs as a result stretches the bowel wall and causes diverticulae to form. They occur like small balloons and can become inflamed, causing pain and diarrhoea.

A high-fibre diet and plenty of fluids can help the symptoms.

Gallstones
The gallbladder stores bile, a digestive juice produced by the liver. Bile is required to digest fatty food. Gallstones are crystal-like deposits that develop in the gallbladder, for a variety of reasons.

Among the causes is incomplete emptying of the gallbladder, as can happen in pregnancy, along with chronic infection in the bile. Excessive fat in the diet can cause the production of excess cholesterol, which solidifies into crystals, forming gallstones.

Too little fat in the diet may also cause gallstones because the gallbladder is underused and the cholesterol has more time to solidify into stones.

Symptoms include pain in the middle and upper right abdomen, which may travel to the right shoulder, back or neck and which can wake the person from sleep. The person may also experience pain inducing nausea and vomiting, and may develop fatty food intolerance. Recurring indigestion and jaundice may also feature.

Gallstones can be prevented by taking plenty of fibre-rich foods, including fruit and vegetables, wholegrain cereals and bran and avoiding excessive alcohol intake. Avoid dramatically increasing or decreasing the intake of fat and consume a moderate level of olive oil. Lecithin, which is found in mayonnaise, yoghurt, eggs, milk and peanuts, can prevent gallstones by keeping cholesterol from solidifying in the gallbladder.

Ulcerative colitis
Ulcerative colitis is a chronic condition characterised by inflammation in the bowel and diarrhoea, abdominal pain and rectal bleeding, which adopt a pattern of relapse and remission.

There is no medical cure for the condition but several drugs are available to suppress the inflammation in the bowel and relieve the symptoms of diarrhoea, abdominal pain and rectal bleeding.

Good nutrition is vital in the management of ulcerative colitis. It is important to stress that the majority of people with ulcerative colitis can be managed adequately without the need for surgery.

There is no universal diet for ulcerative colitis. Each person’s experience of the disease is individual and each person may find that particular foods exacerbate their condition. While some people find that highly seasoned food makes their symptoms worse others do not.

Crohn’s Disease
Crohn’s Disease also causes inflammation of the bowel, resulting in fever, pain, diarrhoea and significant weight loss. In more severe cases, the diarrhoea may contain blood and pus.

While it can affect any part of the bowel, it usually affects the lower end of the small intestine, where it joins the large intestine. The gut wall becomes inflamed, leading to ulcers and fissures, and abnormal passageways between adjacent parts of the gut. The gut can become so narrow that food can become stuck, causing obstruction.

Pancreatitis
Pancreatitis is inflammation of the pancreas, which causes pain in the upper abdomen, slowly building up to a steady persistent pain, which can extend to the back and other areas. The pain can be quite severe. It may also cause nausea and vomiting.

The pancreas produces enzymes that digest fats, proteins and carbohydrates in the small intestine. It also secretes the hormones insulin and glucagon, which regulate blood sugar.

Pancreatitis causes the digestion of the pancreatic tissue by its own enzymes. Enzymes and toxins may also enter the bloodstream, affecting other organs like the heart and lungs.

Alcohol and drug abuse and gallstones may cause pancreatitis, as can trauma, surgery to the abdomen and infections. People with pancreatitis should cease alcohol or drug taking if these are the cause and should also reduce the level of fat in their diet.

If there is significant damage to the pancreas supplementary pancreatic enzymes may be recommended. These assist the process of digestion and help prevent the loss of non-digested nutrients through the gut.

Dry mouth
In the mouth, a reduction in the secretion of saliva can lead to a dry mouth. The medical term for dry mouth is xerostomia. Saliva is the clear, watery solution that is always normally present. It lubricates the mouth so that we can speak and taste our food and helps prevent tooth decay by washing away food and plaque from the surface of the teeth.

People with this condition have a greater risk of tooth decay, gum disease and a range of other illnesses affecting the soft tissues of the mouth. The diet may also be severely affected because food cannot be tasted as it normally would and the process of digestion which normally starts in the mouth does not occur.

For further advice or information, consult your doctor or dietitian/nutritionist

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Welcome | A guide to nutrition | What are functional foods? | Probiotics & your health
Obesity – an Irish epidemic | Nutrition & pregnancy | Your digestive system
The role of vitamins & minerals
| Finland – a case study in healthy eating
Health Calculators