What is obesity?

The definition of clinical obesity is a body mass index (BMI) of 30 or above. BMI is a value that is calculated from your weight and height. For example, for a person weighing 65kg who is 1.7 metres tall the BMI is calculated as follows:

65      = 22.5
(1.72 )

This value indicates whether you are underweight, normal weight or overweight for your height. The ideal BMI is between 18.5 and 25. A person with a BMI between 25 and 30 is classified as overweight. A person with a BMI of 30 or above is classified as clinically obese. Being overweight is associated with increased health risks, which are increased further in obesity (see below).

For the average person, BMI is a good indicator of whether there is a serious weight problem. However, in some circumstances (for example, when the person is an athlete with a heavy musculature) the BMI may be greater than 25 even though the person is not overweight.

The prevalence of obesity in the UK is increasing. For example, the Health Survey for England 2003 showed that 22.2 per cent of men and 23.4 per cent of women were clinically obese, up from 13.8 per cent of men and 17.3 per cent of women in 1994. A Department of Health report published in 2006 predicted that by 2010 a further 2.3 million men and 1.2 million women would be obese compared with 2003.

What causes obesity?

Some people have a greater tendency to put on weight than others, and obesity does tend to run in families. There may be a genetic link but, in addition, diet and eating patterns are often passed on to children from their parents. Therefore, obesity can be caused by a combination of factors. To become overweight, you must eat more calories than the body requires - the excess calories are then stored in the body as fat.

What are the risks of obesity?

The health risks associated with overweight and obesity increase in proportion to your BMI. Hence, the more overweight you are (and the greater your BMI), the greater your risk of developing serious health problems. Overweight people are at an increased risk of death from coronary artery disease, such as stroke and heart attack and have an increased tendency to develop diabetes or gall bladder disease. Obesity has also been linked to some types of cancer. In addition, overweight or obese women who become pregnant are at increased risk of hypertension and diabetes developing during the pregnancy. 

If you have an existing condition, such as hypertension, diabetes or heart disease, these will be exacerbated by an increase in weight.

Osteoarthritis, particularly of weight bearing joints such as the knee, can be increased in people who are overweight, especially middle-aged women. Obesity can also increase the incidence of back pain and shortness of breath.

What treatment is available?

The management of overweight and obesity involves balancing the intake of energy (calories from food) against output of energy (energy used by the body). If intake is greater than output the excess energy will be stored as body fat. Therefore, a change in diet and lifestyle is necessary to achieve weight loss. Advice from a doctor should always be sought initially. Referral to a dietitian may be necessary, particularly if you have an existing disease such as diabetes.

There are many slimming clubs and associations that can help to increase your motivation to lose weight and which offer dietary advice and emotional support. Changes in diet are necessary - you need to increase your intake of fruit and vegetables and to decrease excess calorie intake, particularly excess calories from fat. In addition to dietary adjustment you should also increase your energy output by increasing the amount of exercise you do. Besides aiding weight loss, exercise has also been shown to be beneficial in the prevention of diseases such as coronary heart disease and diabetes. However, advice from an expert should be sought before a fitness programme is started.

Sometimes a doctor may feel that it is appropriate to prescribe medical treatment to help weight loss. The medicines available must always be given in conjunction with a low calorie diet. They can only help if they are used in addition to dieting and will not be successful without dietary changes.

Bulking agents such as methylcellulose (eg, Celevac®) create a feeling of fullness in the stomach and may help to alleviate hunger.

Orlistat (eg, Beacita®, Xenical®) is a drug treatment available for use in obesity. It is only recommended for people with a BMI of 30 or over (or for overweight people with a BMI of 28 or over and associated risk factors). Orlistat is a lipase inhibitor, which acts by inhibiting the amount of fat absorbed from the diet. The level of fat consumed must be restricted while taking these tablets.

Liraglutide (Saxenda®) is another, newer drug treatment available for the treatment of obesity. It is recommended for use in people with a BMI of 30 or over (or for overweight people with a BMI or 27 or over and associated risk factors). Liraglutide belongs to a group of drugs called GLP-1 agonists. It is thought to regulate appetite by increasing feelings of fullness and satiety while lowering feelings of hunger.

Self-help measures:

  • Seek help from a doctor or other health professional and find out what help is available in your area
  • Try to increase the amount of fresh foods such as fruit and vegetables in your diet. Aim for at least five portions a day (not including potatoes)
  • Reduce your intake of dairy products such as cheese, full-fat milk and butter. Choose low-fat versions and eat in moderation
  • Limit snacks such as cakes, biscuits, chocolate and crisps which all contain a high percentage of fat
  • Grill food instead of frying and eat lean meat such as fish and chicken or meat with the fat removed
  • Be aware of the hidden calories in alcohol and try to limit your intake
  • Take more exercise, after seeking advice from your doctor

Further information available from:

British Nutrition Foundation
Imperial House 6th Floor
15-19 Kingsway
London WC2B 6UN
Tel: 020 7557 7930
Email: postbox@nutrition.org.uk
Internet: www.nutrition.org.uk

The British Dietetic Association
5th Floor, Charles House
148/9 Great Charles Street Queensway
Birmingham B3 3HT
Tel: 0121 200 8080
Email: info@bda.uk.com  
Internet: www.bda.uk.com

Fact sheet provided by MIMS

Date last reviewed: November 2008

MIMS Clinics

Prescribing news and resources for key therapeutic areas, collated by the MIMS editors.

Register or Subscribe to MIMS

GPs can get MIMS print & online and GPonline for free when they register online – take 2 minutes, and make sure you get your free MIMS access! If you're not a GP, you can subscribe to MIMS for full access.

Register or subscribe

MIMS bulletins

News and updates straight to your inbox.

Prescribing Update: Fortnightly news bulletin
Urgent prescribing updates
Spotlight: Disease-themed monthly round-up

Sign me up

MIMS Dermatology

Read the latest issue online exclusively on MIMS Learning.

Read MIMS Dermatology

Mobile apps

MIMS: access the full drug database and quick-reference tables on the go

MIMS Diagnosis and Management: concise information on signs and symptoms, investigations and diseases

Promo Image

Clinical calculators

Handy calculators and conversions for primary care.