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Page last reviewed: 13/07/2011

Obesity is when a person is carrying too much body fat for their height and sex. A person is considered obese if they have a body mass index (BMI) of 30 or greater.

Today's way of life is less physically active than it used to be. People travel on buses and cars, rather than walking, and many people work in offices, where they are sitting still for most of the day. This means that the calories they eat are not getting burnt off as energy. Instead, the extra calories are stored as fat.

Over time, eating excess calories leads to weight gain. Without lifestyle changes to increase the amount of physical activity done on a daily basis, or reduce the amount of calories consumed, people can become obese.

How common is obesity?

In 2011 the National Adult Nutrition Survey conducted by the Irish University Nutrition Alliance showed that 26% of men and 21% of women were obese.In the same year the National Longitudinal study of Children showed that 19% of 9 year olds were overweight and a further 7% were obese.

The number of overweight and obese people is likely to increase. The Foresight report, a scientific report used to guide UK government policy, has predicted that by 2025, nearly half of men and over a third of women will be obese. 


Obesity can cause a number of health problems, such as type 2 diabetes (a condition caused by too much glucose in the blood), and heart disease (when the heart's blood supply is blocked).

Being overweight or obese can also shorten life expectancy (how long a person should live). In obese adults over 40 years of age, obesity can shorten life expectancy by 6-7 years. 

Obesity is treated by losing weight, which can be achieved through a healthy, calorie-controlled diet and increased exercise. The lifestyle changes necessary for long-term weight loss can be challenging to achieve, but there is a wide range of support available.

Surgery can be used to treat people who are severely obese and have tried other methods of weight loss with no success. There are a variety of techniques, although these do carry risks and may not be suitable for everyone.

Definition of obesity

Obesity can be measured in different ways. An easy way is to simply step on the scales and compare your actual weight with your ideal weight.

The most widely used way to measure your weight is to calculate your body mass index (BMI). This is your weight in kilograms divided by your height in metres squared.

  • If your BMI is between 25 and 29.9, you are over the ideal weight for your height (overweight).
  • If your BMI is between 30 and 39.9, you are obese.
  • If your BMI is over 40, you are very obese (known as ‘morbidly obese’).

The BMI calculation cannot take into account if you are particularly muscular, or if you are going through puberty (when your body is still developing).

Page last reviewed: 13/07/2011

Being a little bit overweight may not cause too many noticeable problems. However, once you are carrying a few extra kilograms (or pounds), you may develop symptoms that affect your daily life.

Short-term problems

Day-to-day, obesity causes problems such as:

  • breathlessness,
  • increased sweating,
  • snoring,
  • difficulty sleeping,
  • inability to cope with sudden physical activity,
  • feeling very tired every day, and
  • back and joint pains.

Long-term problems

Obesity can also cause changes that you may not notice, but that can seriously harm your health, such as:

  • high blood pressure (hypertension), and
  • high cholesterol levels (fatty deposits blocking up your arteries), and 
  • type 2 diabetes - a chronic (long-term) condition that is caused by too much glucose in the blood.

In the longer term, obesity greatly increases your risk of a number of serious medical conditions. See the complications section for details of these.

Psychological problems

In addition to the day-to-day problems of obesity, many people may also experience psychological problems (problems to do with mental health). These may include:

  • having low self-esteem,
  • having a poor self-image (not liking how you look),
  • having low confidence levels,
  • feeling isolated in society, or
  • having reduced mobility leading to a poor quality of life.

These can affect your relationships with family members and friends, and if they become severe, may lead to depression.


Joints are the connection point between two bones that allow movement.
Arteries are blood vessels that carry blood from the heart to the rest of the body.
High blood pressure
Hypertension is when the pressure of the blood in your bloodstream is regularly above 140/90 mmHG.
Cholesterol is a fatty substance made by the body that lives in blood and tissue. It is used to make bile acid, hormones and vitamin D.
The sac-like organ of the digestive system. It helps digest food by churning it and mixing it with acids to break it down into smaller pieces.
The gallbladder is a small organ found just under the liver, which stores bile for digestion.
The heart is a muscular organ that pumps blood around the body.
Obesity is when a person has an abnormally high amount of body fat.

Page last reviewed: 13/07/2011

Obesity does not just happen overnight, it develops gradually from poor diet and lifestyle choices and, to some extent, from your genes (the units of genetic material inherited from your parents).

Lifestyle choices

Lifestyle choices are an important factor in influencing your weight. Eating more calories than you need may be down to unhealthy food choices. For example, unhealthy food choices could be:

  • eating processed or fast food that is high in fat,
  • not eating fruit, vegetables and unrefined carbohydrates, such as wholemeal bread and brown rice,
  • drinking too much alcohol - alcohol contains a lot of calories, and heavy drinkers are often overweight, and
  • eating out a lot - as you may have a starter or dessert in a restaurant, and the food can be higher in fat and sugar,
  • eating larger portions than you need - you may be encouraged to eat too much if your friends or relatives are also eating large portions, and
  • comfort eating - if you feel depressed or have low self-esteem you may comfort eat to make yourself feel better.

Unhealthy eating habits tend to run in families, as you learn bad eating habits from your parents. Childhood obesity can be a strong indicator of weight-related health problems in later life, showing that learned unhealthy lifestyle choices continue into adulthood.

Lack of physical activity

Lack of physical activity is another important factor that is related to obesity. Many people have jobs that involve sitting at a desk for most of the day, and rely heavily on their cars to get around. When it is time to relax, people tend to watch TV, or play computer games, and rarely take any regular exercise.

If you are not active enough, you do not use up the energy provided by the food you eat, and the extra calories are stored as fat instead.

The National Guidelines on Physical Activity for Ireland recommend that adults do at least 150 minutes (2 hours and 30 minutes) of moderate-intensity aerobic activity (i.e. cycling or fast walking) every week.


Some people tend to stay the same weight for years without much effort, whereas others find they put on weight quickly if they are not careful about what they eat. This could be due, in part, to your genes.

Some genetic conditions can increase your appetite, so you end up eating too much. There are also genes that determine how much fat your body stores. A particular genetic variation could mean that your body is more likely to store fat than somebody else. 

Medical reasons

Medical conditions that can cause weight gain include:

  • Cushing's syndrome - a rare disorder that causes an over-production of steroid hormones (chemicals produced by the body),
  • an under-active thyroid gland (hypothyroidism) - when your thyroid gland does not produce enough thyroid hormone (called thyroxine, or T4), and
  • polycystic ovary syndrome (PCOS) - when women have a large number of cysts in their ovaries.

Certain medicines, including some corticosteroids and antidepressants, can also contribute to weight gain. Weight gain can also be a side effect of taking the combined contraceptive pill, and from quitting smoking.



Obesity is when a person has an abnormally high amount of body fat.
Genes contain information that you inherit from your parents, such as eye or hair colour. They are carried by chromosomes.
The thyroid is a jointed piece or cartilage that enclosed the vocal cords and forms the Adam's apple in men.
Antidepressant medicine is used to treat depression. For example Fluoxetine, Paroxetine.

Page last reviewed: 13/07/2011

Body mass index (BMI) is currently used as the most accurate and reliable way of measuring how overweight you are. You can use the healthy weight calculator to calculate your BMI. You will need to know your height and your weight.

For most adults, a healthy weight is having a BMI between 18.5 and 24.9. A BMI between 25 and 29.9 is considered overweight. A BMI over 30 is considered obese.

The BMI calculation cannot take into account very muscular figures. Muscle can add extra weight, and this may give you an overweight or obese BMI, when you are not an unhealthy weight. For example, a heavyweight boxer would be classed as obese using the BMI, when he is in fact a healthy weight.

Though for most people, BMI remains an accurate method of assessing their weight.

Children and young people should not use BMI to calculate if they are a healthy weight, as their bodies are still developing. Instead, children and young people should visit their GP, who will be able to tell them if they are overweight or obese for their height and sex.

Most modern leisure centres have weighing scales that can electronically measure the percentage of your body weight that is fat. This can be compared with what would be ideal for you depending on your height, age and sex. This may give you an indication of how overweight you are.

Visiting your GP

If you are overweight or obese, you should visit your GP to find out if you are at increased risk of health problems, and how you can safely lose weight. Your GP will ask about:

  • any underlying causes for your obesity - for example if you are on certain medication or if you have a medical condition that causes weight gain,
  • your lifestyle - particularly your diet and how much physical activity you do, and also whether you smoke, and how much alcohol you drink,
  • how you feel about being overweight - for example, if you are feeling depressed about it,
  • how motivated you are to lose weight, and
  • your family history of obesity and other health conditions, such as diabetes (a condition caused by too much glucose in the blood).

Further tests 

As well as calculating your BMI, your GP may also perform some further tests. These will help determine if you are at increased risk of any heath complications because of your obesity. These could include:

  • measuring your blood pressure,
  • measuring your waist circumference (the distance around your waist), and
  • measuring the glucose (sugar) and lipid (fat) levels in a sample of your blood.

Your GP may also consider your age and ethnicity, as these can affect your risk of certain conditions. For example, some people of Asian, African or Afro-Caribbean ethnic groups may be at increased risk of high blood pressure (hypertension), and some older people may be at lower risk.

Page last reviewed: 13/07/2011

The aim of treatment for obesity is to lose weight in order to improve your general quality of life, both physically and psychologically (see symptoms). For example, losing weight may help you sleep better, or help you to improve your self-esteem.

The best way to treat obesity is to reduce the amount of calories in your diet and to exercise more. The type of diet and exercise that will benefit you, and that you can follow safely, will vary from person to person. You should visit your GP before making any significant changes to your lifestyle.

Diet advice

A healthy diet should contain:

  • meals based on starchy, high-fibre carbohydrates, such as wholegrain bread, pasta and rice
  • at least five portions of fruit and vegetables every day
  • a moderate amount of low-fat protein, milk and dairy products
  • a very small amount of foods that are high in fat, sugar or salt

In order to lose weight, you need to eat a healthy diet and reduce the amount of calories in your diet. This will mean changing your eating habits. You need to do this a way that you find acceptable, and that you can maintain long-term (see tips for weight loss, in the box to the right).

Types of diet

Your GP may recommend a calorie-controlled diet. This will be based on how much you are currently eating, and then attempting to cut the amount of calories you eat every day by around 600. Alternatively, you may be advised to follow a low-fat diet. See diet for tips to cut down the amount of fat and sugar in your diet.

A calorie-controlled or low-fat diet should only be attempted with expert support and advice. You should also have a follow-up appointment with your GP to check your progress.

If you attempt a low-calorie diet (only 1,000-1,600 calories a day) without the advice of a health professional, you may miss out some of the vital nutrients you need to stay healthy.

Very-low-calorie diets (VLCDs) may be used by people who are obese and have reached a plateau in their weight loss. The National Institute of CinicalExcllence in the UK defines VLCDs as being less than 1,000 calories a day. They should only be used with expert support and any diet of less than 600 calories a day should be used only under the supervision of a qualified health professional.

Diets that are very restrictive, for example, those that cut out entire food groups, should not be used. This includes diets that cut out all carbohydrates or proteins. These diets are not usually sustainable in the long-term and may be harmful. 

Children and diet

As children are still growing, they may need to follow a special kind of diet to make sure that they are still getting all the nutrients they need to develop healthily. If your child is overweight or obese, consult your GP before making any significant changes to their diet.

Increase your exercise

Research suggests that increasing the amount of exercise you do is an effective way to lose weight, and the results are even better when combined with changes to your diet.

The advice from your GP about exercise will vary depending on how fit you are to start with, and what it is safe for you to do. You should start by decreasing the amount of time you are physically inactive, such as how long you spend watching television or sitting at a computer.

You should then build up slowly to at least 150 minutes (2 hours and 30 minutes) of moderate-intensity aerobic activity (i.e. cycling or fast walking) every week.

Moderate intensity means that you are breathing slightly more than normal, but you can still comfortably talk as you exercise. For more information go to www.getirelandactive.ie

Types of exercise

The most effective types of exercise are 'aerobic' activities. Aerobic activities are any kind of rhythmic, moderate intensity exercises that use the large muscles in your legs and buttocks. The exercise should raise your heart rate and make you breathe harder. 

Recommended types of physical exercise include:

  • activities that can be incorporated into everyday life, such as brisk walking, gardening, or cycling,
  • supervised exercise programmes, and
  • activities such as swimming, walking (where you aim to walk a certain number of steps a day), and stair climbing.

Chose physical activities that you enjoy, as you are more likely to continue doing them.

Further information

Children and exercise

Children should be encouraged to do at least 60 minutes of moderate activity each day. The activity can be in one session, or several sessions that last 10 minutes, or more. As with adults, children who are overweight, or obese, may need to do more than 60 minutes of exercise. You should check with your GP before your child starts a new exercise programme.


Medication for obesity may be available from your GP in some cases. You need to show you can lose weight on a calorie-controlled diet before it is considered. Medication is normally one part of a weight loss programme and requires a long-term change in lifestyle for lasting results.

The only medication currently prescribed is orlistat. See the box to the left for information on sibutramine, which is no longer used due to safety concerns.


Ortlisat works by blocking the action of an enzyme (a protein that speeds-up and controls chemical reactions in the body) that is used to digest fat. The undigested fat is not absorbed into your body, and is passed out with your faeces (stools). As you are absorbing less fat, you should lose weight.

One orlistat capsule is taken with each main meal (a maximum of three capsules a day). You can take the capsule either before, during, or up to one hour after each meal.

If you miss a meal, or the meal does not contain any fat, you may not need to take the orlistat capsule. Your GP should explain this to you, or you can check the patient information leaflet that comes with your medication.

You have to have made significant effort to lose weight through diet, exercise or changing your lifestyle before taking orlistat. Even then, orlistat is only prescribed if you are on a low calorie diet and you have:

  • a body mass index (BMI) of 28 or more, and other conditions related to weight, such as high blood pressure (hypertension), or
  • a BMI of 30 or more.

Treatment with orlistat must be combined with a low fat diet and other weight loss strategies, such as doing more exercise. If you are prescribed orlistat, you will also be offered advice and support about diet, exercise and making lifestyle changes.

Treatment with orlistat should only continue beyond three months if you have lost 5% of your body weight. Orlistat usually starts to affect how you digest fat within 1-2 days. If orlistat has not worked after three months, it is unlikely to be an effective treatment for you.

If you have type 2 diabetes (a condition caused by too much glucose in the blood), it may take you longer to lose weight using orlistat. Your target weight loss after three months may therefore be slightly lower.

If orlistat is successful after three months, your prescription may be continued for up to a year. After that, your GP will review your condition and decide whether you should continue with orlistat or not. 

Side effects and warnings

Side effects of orlistat include:

  • fatty or oily stools,
  • needing the toilet urgently,
  • passing stools more frequently,
  • oily discharge from your rectum (the storage area at the end of the bowel that holds the stools) - you may have oily spots on your underwear, 
  • flatulence (wind),
  • abdominal (stomach) pain,
  • headaches, and
  • upper respiratory tract infections - such as a cold or sore throat

Side effects are much less likely if you stick to a low fat diet.

Women taking an oral contraceptive pill are advised to use an additional method of contraception, such as a condom, if they experience severe diarrhoea while taking orlistat. This is because if you have diarrhoea, your contraceptive pill may not be absorbed by your body, and so may not be effective.

Orlistat is not prescribed to:

  • pregnant women
  • breastfeeding women
  • children

Children and medication

The use of medication to treat obesity is usually not recommended for children (under 18 years of age). In exceptional circumstances, for example if their obesity places their life in danger, orlistat may be considered for children over 12 years of age, with specialist supervision.

Tips for weight loss

  • Set realistic weight loss goals – aim for 5-10kg (11-22lb) over three months. This is around 0.5kg (1.1lb) a week, but reduce this target if it seems too difficult.
  • Eat regular meals and try reducing the size of your portions.
  • Contact a local slimming club if you think this may help you.
  • Tell your friends and family that you are trying to lose weight, as they can help motivate you.
  • Drink less alcohol, as it is high in calories. 
  • Consider using a food diary to keep track of the amount of calories you are eating, and the changes you are making to your diet.

Page last reviewed: 13/07/2011

Weight loss surgery, also called bariatric surgery, has been found to be an effective treatment for some obese people. However, it is only available if your obesity is affecting your health and other treatment options have been tried and have not worked.

The National Institute for Health and Clinical Excellence (NICE) in the UK recommends that weight loss surgery should only be offered if all the following conditions apply:

  • You have a BMI of 40 or more, or you have a BMI of 35-40 and a serious health condition that could be improved if you lose weight, such as type 2 diabetes or high blood pressure.
  • You have tried all the appropriate non-surgical methods, such as diet and exercise, but have failed to achieve or maintain a beneficial level of weight loss for at least six months.
  • You agree to commit to long-term follow-up treatment after surgery at a specialised obesity service.
  • You are fit and healthy enough to withstand the anaesthetic (painkilling medication) and surgery.

In most cases, you need to be  referred for surgery by a specialist obesity management service (not just your GP).

For more information, including how the surgery works, how it is carried out and your recovery afterwards, read the Health A-Z pages on Weight loss surgery

Page last reviewed: 13/07/2011

Being obese can lead to a number of serious health problems, as well as shorten your life expectancy (how long you should live).

Health problems

Being overweight or obese can increase your risk of a number of health problems, including:

  • high blood pressure (hypertension) - this is a major risk factor for developing a serious cardiovascular disease (conditions that can affect the circulation of blood around the body),
  • infertility - when you cannot get pregnant despite having regular unprotected sex,
  • type 2 diabetes - a chronic (long-term) condition that is caused by too much glucose in the blood,
  • many types of cancer - when the body's cells begin to grow and reproduce in an uncontrollable way,
  • heart disease - when your heart's blood supply is blocked, 
  • stroke - when the blood supply to the brain is interrupted.
  • asthma - when the airways of the lungs (the bronchi) become inflamed (swollen),
  • osteoarthritis - a condition that affects the joints,
  • chronic (long-term) back pain - particularly lower back pain, and
  • depression - when you have feelings of extreme sadness, despair or inadequacy that last for a long time.

Page last reviewed: 13/07/2011

The best way to prevent becoming overweight, or obese, is by eating healthily and exercising regularly. As obese children also tend to be obese in later life, it is very important for parents to set the right example to their children from an early age.

Content provided by NHS Choices www.nhs.uk and adapted for Ireland by the Health A-Z.

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