Obesity (excess body fat) is an increasingly important issue in Australia. Doctors use the body mass index (BMI) to determine whether a person’s weight is in the healthy range. To calculate your BMI, divide your weight in kilograms by your height in metres squared. For example, if you weigh 70 kg and you are 1.7 m tall, your BMI is (70 / 1.7 x 1.7) = 24.2 kg/m2. A BMI of 25 kg/m2 or more indicates that you are overweight, while a BMI of 30 kg/m2 or more indicates that you are obese.
Obesity can cause problems with many organs in the body — view this animation to discover why obesity is bad for your health.
Being obese can increase your risk of stroke. In obesity, the arteries in the brain can become narrowed by fatty deposits (atherosclerosis).
Blood clots may then form, blocking the supply of blood to the brain and causing a stroke.
Obesity is also associated with high blood pressure, another factor that increases the risk of stroke.
Obesity is strongly linked to obstructive sleep apnoea, a condition in which the airway partially collapses during sleep.
Obstructive sleep apnoea is more likely in obese people than in other people because of fat deposited in the neck area.
Approximately 60–70 per cent of people with obstructive sleep apnoea are obese. The good news is that weight loss can improve obstructive sleep apnoea.
Obese people often have abnormal levels of cholesterol and other blood fats. This encourages fatty deposits to build up in the walls of arteries (atherosclerosis). If atherosclerosis narrows the arteries supplying the heart, angina (chest pain) or heart attack can occur. This situation is known as coronary heart disease.
Obesity in childhood sets the scene for heart and blood vessel disease in adulthood.
Obesity makes it hard to breathe easily — it reduces lung function and weakens the muscles that help us breathe.
Researchers are increasingly recognising the links between obesity and chronic (long-term) breathing difficulties. The association between asthma and obesity is unclear, but research shows that asthma symptoms improve in obese people who lose weight.
High blood pressure is another disease related to obesity — as weight increases, blood pressure tends to rise. High blood pressure may not cause any symptoms itself, but it increases the risk of heart attack and stroke.
Most research has shown that obese people can reduce their blood pressure by losing weight. It’s best to get down to a body mass index (BMI) of less than 25, but losing even approximately 5 kg can reduce your blood pressure enough to lower the risk of dying from stroke or heart disease.
Carpal tunnel syndrome (compression of a nerve in the wrist area causing pain, tingling or numbness of the fingers and a weak grip), is 4 times more common in people who are obese than in people who are not.
After menopause, obese women are at a higher risk of developing breast cancer than women with a body mass index (BMI) in the healthy range.
Weight gain after menopause seems to be especially important when it comes to increasing breast cancer risk. However, even before menopause, women with breast cancer who are overweight are less likely to survive the cancer than those with a lower BMI.
Obesity is also a risk factor for breast cancer in men.
Alcohol-related liver disease — including cirrhosis and hepatitis — is more common in people carrying excess weight than those who are not.
Obesity also increases the risk of fatty liver disease; a range of conditions in which fat accumulates in the liver.
Gallstones are more common in overweight and obese people than in people of normal weight — this can be related to abnormal cholesterol levels.
Gallstones affect one in 3 obese people compared to one in 10 people with a body mass index (BMI) in the healthy range. However, rapid weight loss (more than about 1.3 kg a week) is also a risk factor for gallstones, so more gradual weight loss is recommended.
Obesity is strongly linked to cancer of the oesophagus — the higher your body mass index (BMI), the greater your risk.
Obese people are also more likely than non-obese people to develop cancer of the top part of the stomach (gastric cardia).
Carrying too much weight can be bad for your immune system, reducing your resistance to infections. Scavenger cells, which destroy invading microbes, may not work properly in people who are obese.
Obesity is also associated with an increased risk of infections following wounds and burns.
Research suggests that obesity increases the risk of kidney failure — the higher the body mass index (BMI), the greater the risk of kidney failure. This may be because obesity forces the kidneys to work harder.
Obese people, especially women, are also more likely than other people to develop cancer of the kidney (renal cell cancer).
Obesity is the strongest environmental risk factor for type 2 diabetes, a condition where the body doesn’t respond properly to the hormone insulin. Ninety per cent of people with type 2 diabetes are overweight or obese.
Being obese also makes diabetes hard to control, with diabetes medicines being less effective in obese people than in people whose weight is in the healthy range.
The good news for people who are obese and have type 2 diabetes: lose as little as 5 per cent of your body weight and your blood sugar levels should become more manageable.
Cancer of the colon or rectum (bowel cancer) is more common in obese people than in people with a body mass index (BMI) within the healthy range.
Large waist size (abdominal obesity) seems to be especially important when it comes to developing bowel cancer.
Women who are severely obese are 3 times more likely to have menstrual problems than women who are a healthy weight.
Obese women also have a 3–4 times higher risk of cancer of the endometrium (lining of the womb) than women with a body mass index (BMI) in the healthy range. Women who are obese and also have diabetes have an even greater risk of endometrial cancer.
Obesity reduces fertility in both men and women.
For women, being obese before getting pregnant increases the risk of pregnancy complications like high blood pressure, pre-eclampsia and gestational diabetes.
When it comes to giving birth, obese women seem to be more likely than women of normal weight to have an overdue birth, induced labour or longer labour. Obesity is also linked to an increased Caesarean section rate and greater blood loss during birth, and it increases the risk of complications after labour.
Among women, obesity increases the risk of stress incontinence (leakage of urine when you laugh, cough, sneeze, exercise or lift something heavy) and urge incontinence (a sudden strong urge to urinate, followed by leakage of urine).
Obese people are more likely than people with a body mass index (BMI) in the healthy range to have osteoarthritis, especially of the knee, but also of the hip, hand and lower back.
If you have knee osteoarthritis and you are obese, losing 4.5 kg or more should improve your symptoms.
Obesity also increases the risk of rheumatoid arthritis.
Obesity increases the risk of deep vein thrombosis (DVT), a condition in which blood clots in the deep veins, often in the legs. In people with DVT, a blood clot can break off and lodge in the blood vessels in the lung. This process, called pulmonary embolism, can be fatal.
Carrying too much weight also increases the risk of chronic venous insufficiency — in this condition there is not enough blood flow through the veins back to the heart. This means that blood may pool in the legs, causing swelling and pain with redness, thickening and ulceration of the skin.
Sever’s disease, which causes heel pain in children during the early part of puberty, is more common in obese children than in other children.
Obesity increases the risk of gout, a condition where uric acid is deposited in the joints. The big toe is a common site for gout, but other joints throughout the body can also be affected.
Last Reviewed: 11 June 2010