Last partial update: July 2017 - Please read disclaimer before proceeding
Defining obesity
Obesity is an increasing problem in developed societies due to an increasingly sedentary lifestyle and the ready availability of foods high in fat and sugar. In Australia, the incidence of obesity has reached epidemic proportions. It directly causes about 4.4 per cent of the total burden of disease in Australia and the combination of obesity and physical inactivity is Australia’s greatest health problem.
The average weight of an Australian woman has increased from 67kg in 1995 to 74kg in 2012.
Source: Australian Institute of Health and Welfare 2000 |
The figure above shows that excess weight increases with age. This is partially explained by the increase in fat stores that accompanies increasing age. Fat comprises 20 per cent and 30 per cent of body weight in lean young men and women respectively and 25 per cent and 35 per cent in lean older men & women. (see table below.) Ageing is, however, only a minor factor in causing obesity when compared with poor diet and lack of exercise.
Australia is fast becoming a ‘takeaway food society’. Thirty-three per cent of money spent on food is used to purchase foods prepared and eaten outside the home. Most of these foods have a high fat content that is high in saturated fat. They are also usually high in energy (calories/kilojoules). Even so-called ‘low fat’ foods, such as low fat biscuits, muffins etc., are sometimes still relatively high in fat and they usually still have the same high energy content. A change towards healthier low-fat, low-energy foods is needed to ward off diseases associated with obesity, such as those outlined below.
Body fat as a percentage of body weight in people |
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Women (% fat) |
Men (% fat) |
Essential fat |
10-12% |
2-4% |
Athletes |
14-20% |
6-13% |
Fittness |
21-24% |
14-17% |
Acceptable |
25-31% |
18-25% |
Obese |
32% plus |
25% plus |
* Minimum fat level needed to maintain normal body functioning. |
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Fat distribution and Brown fat verses white fat
Fat distribution: Fat distributed around the abdomen is more harmful that fat distributed in the buttochs or the limbs. Abdominal fat is also more harmful if the person has a low musclewe mass generally.
White and Brown Fat: White fat is the fat that people acculmulate as a way of storing energy and it is the fat that is associated with obesity. Brown fat is a tissue that burns sugar and fat andin doing so generatesheat to keep us warm. It also helps us loose weight and thus people with more brown fat are leaner and have lower sugar levels. It is mostly located around the shoulder reguion and large levels are present in babies. In adults its production can be stimulated by exposing the body to cold conditions. People with brown fat tend to have more stable blood sugar levels.
The BMI - a way of measuring obesity
To minimise their risk of illness from being overweight, people need to keep within a normal weight range and not increase their weight during adult life. After the age of 25,the risk of developing diabetes or coronary artery disease is increased with any weight gain over 5 kg in female and with any weight gain at all in males. There are two methods used to define obesity.
The traditional way of defining weight categories is by using the Body Mass Index (BMI), which can be calculated using the formula below or from the graph available on this web site. The table below shows the generally accepted weight categories for BMI readings. Anyone with a BMI of 25 or above is classified as having an excess weight problem.
BMI = Weight (in kg)
Square of Height( in m)
For example, if a person weighed 75kg and were 1.70m tall -
BMI = 75 divided by 1.7 squared = 75 divided by 2.89 = 26.0
It is worth noting that most makes of bathroom scales are only accurate up to about 120kg. More accurate scales are needed for measuring people heavier than this weight.
Weight category according to ethnic group (as measured by BMI level)
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Ethnic group |
Overweight |
Obese |
Caucasian |
25 to 29.9 |
30 and over |
Asian |
23 to 24.5 |
25 and over |
Polynesians |
26 to 31.9 |
32 and over |
Also of concern is the fact that 20 per cent of young women in Australia are classified as underweight. This causes health problems, such as osteoporosis or weak bones, and very underweight people also have an increased mortality rate. This is discussed further in the section on childhood obesity. |
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The significance of a high BMI does to some extent depend on the amount of fat and muscle in the body. A person with a high proportion of muscle compared to fat, such as an athlete, and who also has a slightly high BMI, is less likely to suffer from ill health than an unfit person with the same BMI. Inversely, a person with a lowish BMI who has a relatively high amount of body fat and is very unfit (i.e. has relatively little muscle), can be at increased risk of ill health.
Abdominal obesity (waist size) and disease
While obesity has traditionally been defined in terms of a person’s BMI, it is the distribution of fat in the body that has the major influence on health. Excess abdominal fat, the so-called barrel-shaped body, increases the risk of heart attacks, high blood pressure, non-insulin dependent diabetes, lipid disorders, gall bladder disease and breast cancer, all of which are part of the ‘dangerous’ Metabolic Syndrome. (See boxed section.) There is less disease associated with excess fat distributed around the hips (i.e. a ‘pear-shaped’ body). Abdominal fat is composed of fat under the skin (two thirds) and fat surrounding the organs in the abdominal cavity, termed visceral fat, (one third).
Abdominal causes health problems in several ways. Firstly, abdominal fat releases compounds (adipocytokines) that increase arterial (blood vessel) damage. It is thought that this might be due to visceral fat outgrowing its blood supply and the resultant lack of oxygen to this fat tissue causes damage that triggers the release of these compounds. Secondly, and most importantly, the fat in the abdominal cavity is responsible for causing increased insulin resistance. (This is partly caused by the above mentioned compounds.) Increased insulin resistance means that the insulin produced by the pancreas is not as efficient at maintaining normal blood sugars. Initially the body copes by producing more insulin. However, if the situation worsens, the body can not produce enough insulin and blood sugar (glucose) levels start to rise above normal levels. If severe, blood sugar readings may reach levels high enough for diabetes to be diagnosed. This situation is an even bigger problem in older people as insulin secretion decreases with age. Even if diabetes does not develop, increased insulin resistance is still harmful as it is associated with deleterious changes in blood fats (a lowering of HDL or good cholesterol and an increase in triglycerides). It is a major factor in causing cardiovascular disease. Finally, intra-abdominal fat also breaks down more easily, releasing free fatty acids that can damage the liver and other organs.
The degree of abdominal obesity can be gauged from measuring waist circumference, which is generally considered to be a better measure of likely illness due to obesity than the BMI reading. Normal and abnormal waist circumference readings are shown in table 13. Males with a waist circumference over 100cm and females with a waist circumference over 90cm need to be especially concerned with reducing their waist size. It is important to realise that people can have a BMI at the upper end on the normal range and still have an abnormally large waist measurement that increases their risk of illness due to obesity.
Waist measurements in relation to health risk |
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|
Ideal waist Measurement |
Moderately increased waist measurement |
Seriously increased waist measurement |
Men |
Less than 94cm |
94 to 102 cm |
Greater than 102cm |
Women |
Less than 80cm |
80 to 88 cm |
Greater than 88cm |
Vascular disease and diabetes risk due to level of obesity |
Normal |
Moderately increased |
High |
Notes: 1. The waist should be measured at the level of the naval. 2. Waist measurements should be about 10cm lower for Indian and Asian people. 3. Waist measurements are a better predictor of vascular disease risk than BMI levels. |
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Disease caused by obesity
Source – Adapted from Australian Institute of Health and Welfare: Begg, S. et al: 2007. |
Excessive weight is responsible for close to five per cent of all illness in Australia with central obesity being the biggest problem. The numerous consequences of obesity are detailed below and figure 10 shows their contribution to total burden of disease caused by obesity. The burden of disease due to obesity is maximum in the 45- to 65-year age group in men and in the 55- to 75-year age group in women. Individuals who are obese (i.e. have a BMI over 30) have a 50% to 100% increased in risk of dying prematurely.
Luckily, losing weight does help greatly. For example, a 9 kg weight loss in an otherwise well, obese woman aged between 40 and 65 can give a 25 per cent reduction in overall mortality.
The overall treatment of obesity should include looking for and treating appropriately conditions that are caused, at least in part, by obesity (such as diabetes, sleep apnoea and high blood pressure), and conditions (such as raised cholesterol or blood pressure) that may exacerbate the obese person’s already increased risk of cardiovascular disease.
Coronary artery disease (and resultant sudden death)
Obesity is associated with several factors that increase the risk of coronary artery disease, including an increased work load on the heart, increased blood pressure, and increased vascular disease due to deleterious changes in blood lipids, including reduced HDL and increased LDL (bad cholesterol). This situation is worse in people suffering from the ‘metabolic syndrome’.
Heart failure
OAs well as causing coronary artery disease, there is evidence that obesity causes gradual mild injury to heart muscle that over time can leads to significant heart muscle damage / reduces heart muscle function i.e. causes function failure. This is independent of the affect obesity has on cardiovascular risk factors such as high blood pressure, high cholesterol and diabetes.
Diabetes type 2 (non-insulin dependant diabetes)
This type of diabetes, which occurs mostly in adults, is responsible for 90 per cent of diabetes in Australia and is closely related to obesity levels. If people have a BMI of say 22, they are very unlikely to get diabetes. However, if a person is overweight with a BMI of 25 to 30, his or her risk of developing diabetes increases nine fold. Very over weight people with a BMI greater than 35 have a diabetes incidence about twenty times that of a normal weight person. Obesity is a principal cause of increased resistance to the hormone insulin and it is this insulin resistance that is responsible for type 2 diabetes in over weight people.
Cancer
Obesity increases the risk of developing a variety of cancers, with about 14 per cent of the disease burden caused by obesity is due an increased incidence of cancer. Obesity is thought to be directly responsible for about three per cent of cancer deaths in Australia.
In obese women, the extra fat tissue present causes increased production of the hormone oestrogen and this extra oestrogen increases the risk of developing postmenopausal breast cancers and endometrial cancer (cancer of the uterus or womb). They occur to a greater extent in people who have abdominal rather than ‘hip’ obesity. Other cancers increased by obesity include colon, kidney, and digestive tract cancers.
Cancer attributable to obesity |
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Type of cancer |
Proportion of cancer type attributable to obesity |
Colon |
11% |
Breast cancer (post menopausal only) |
9% |
Uterine (endometrial) |
39% |
Renal |
25% |
Oesophageal (adenocarcinoma) |
37% |
Gall bladder |
24% |
Source: Cancer Council of Australia: National Cancer Prevention Policy 2004-06, pp66-7 |
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Gall Bladder Disease and liver disease
Cholesterol is excreted from the liver into the intestine via the bile ducts and the gall bladder. This cholesterol is a major component of most gall stones. Increased gall bladder disease in obese people is probably due to increased secretion of cholesterol from the liver into the gall bladder.
Fatty liver disease is common in Australia, affecting up to 20 per cent of the population. It is caused by fat deposited in the liver damaging the liver tissue and is more common in obese people. It also occurs in people with diabetes or high blood triglycerides. Generally fatty liver disease produces few symptoms and is only found when tests of liver function are performed. However, in severe cases it can go on to cause significant liver damage. Weight loss and abstinence from alcohol have been shown to reduce liver damage associated with this problem. This problem is the third largest reason for liver transplantation in the USA, a situation that will only worsen as the number of obese people increases.
Arthritis – Osteoarthritis and gout
Obesity is associated with increased wearing out of joints (osteoarthritis) in both weight-bearing joints, such as the hips, and non-weight-bearing joints, such as those in the hands. Gout is also increased by obesity, due to impaired uric acid clearance from the kidney. (Uric Acid is the compound that causes gout.) Obesity is associated with as many as 40 per cent of gout cases.
Obesity and pregnancy and infertility
Excess maternal weight increases the risk of premature birth and foetal death and increases the risk of the mother developing diabetes and high blood pressure during the pregnancy, both of which can adversely affect both the baby and the mother. It also increases the likelihood of delivery by caesarian section.
For overweight women, losing weight before becoming pregnant is one of the most important things that they can do to reduce risk to both the mother and the baby.
Obesity can also cause infertility and many overweight women who have problems conceiving fall pregnant following significant weight loss.
Hormone (endocrine) problems
In females, abdominal obesity is associated with increased levels of androgens (male hormones). This can cause masculinising features such as facial hair growth.
Extremely obese men have a decreased testosterone (a male hormone) level which causes feminizing features, such as breast enlargement.
Heart failure can also be increased by obesity
There is evidence that heart failure can increase the incidence of heart fallure in older adults. It does this by itself and through increasing other risk factors for heart disease, such as hypertension and diabetes.
Depression, sleep apnoea and other problems
There is evidence that obese people with a BMI greater than 30 are more likely to suffer from depression. Whether the depression or the obesity comes first is uncertain.
Significant obesity is a common cause of sleep apnoea. This can be helped with continuous positive airways pressure machines, hopefully while weight loss is being achieved.
Reflux, stress incontinence, skin problems, back pain, fatigue and shortness of breath with exercise, social isolation, and psychological problems may also occur when someone is obese.
Heart failure is also more common in overweight individuals and there is recent evidence that obese people may have an increased risk of stroke.
Prevention of obesity in adults
By far the best way to avoid obesity and its associated problems is to avoid becoming overweight in the first place. Once people are overweight, losing weight and maintaining that weight loss is difficult.( It is thus very unfortunate that many people develop obesity in childhood.)
There are specific times during life where weight gain is more likely. These need to be anticipated and managed appropriately through increased exercise or decreased energy intake.
Danger times for developing obesity
Childhood: The cornerstone of healthy weight management throughout life is having a healthy home environment during childhood, where good food and physical activity are encouraged. It is vital that people provide this sort of environment for their children. The older children are when obese, the more likely they are to become obese adults.
Families where obesity is a chronic problem that appears in several generations need to be particularly vigilant to ensure their home environment is a healthy one, as their children may have a significant genetic predisposition to developing obesity.
Adolescence / early adulthood: Inactivity, especially for girls, predisposes adolescents to obesity. Weight that is gained after growth in height has finished is more difficult to remove.
Males are usually active and grow quickly during their adolescence and they need a high energy diet at this time. They finish growing in late adolescence and this is also often the time that they stop playing sport. Unfortunately, they are used to a diet high in energy, often provided by ‘junk food’, and tend to stay on it. This means that they are now taking in more energy than they are using and the excess is stored as fat. The same is true for females, although to a lesser extent. Females finish growing earlier, with most girls reaching their maximum height by 15 years of age. Thus they are likely to start putting on weight earlier.
For both sexes, late adolescence is also the time alcohol consuming starts. Alcohol contains high amounts of energy and the extra energy that this adds to the young person’s diet is often quickly added as fat to their waist-line; and, to make matters worse, alcohol is often consumed with high-energy snack foods like peanuts and crisps.
Click here for section about childhood obesity in childhood and how to prevent it.
Pregnancy: Pregnancy itself does not usually cause abnormal weight gain. However, stress levels are often high during this time and after delivery and this can lead to weight gain, especially if depression is a significant problem. Other factors that increase the likelihood of an overall weight gain several months after delivery include a large weight gain with the pregnancy, a greater number of pregnancies, a later return to work after the pregnancy, and not breast feeding. (The additional energy needed for breast feeding can lead to some weight loss.)
Menopause: A slight weight gain is common around this time in most women, mainly due to lifestyle changes such as reducing levels of physical activity and more time for socializing. Fat is also redistributed from the hips to the abdomen at this time; a bad change. There is no evidence that hormone replacement therapy increases this slight ‘natural’ weight gain.
Life events: Any major life event has the potential to cause weight gain, either because of the stress involved or because the event causes lifestyle changes, such as less time for exercise. Such events might include the death of a parent or spouse, retirement, marriage, or a new relationship.
Quitting smoking: Weight gain is common with ‘quitting’ and occurs due to a decrease in the body’s metabolic rate, improvements in taste, and increased appetite. Before quitting, it is essential to get dietary advice as weight gain is a common cause of ‘quit’ failure. (See section on quitting smoking.)