Obesity

 Obesity is defined as having a Body Mass Index (BMI) over 30 kg/m²

 Other measures used to define obesity are hip-to-waist ratio and percentage body fat

 Obesity is increasing in the Western world and has been estimated to be responsible for 300 000 excess deaths each year

 The medical complications of obesity include diabetes, hypertension, heart disease, gallbladder disease and cancer

Obesity can be prevented by careful attention to the risk factors which predispose someone to the condition

 Obesity can be treated using lifestyle intervention, and where this fails drug treatment

 

What is obesity?

Obesity is defined using a measure called the Body Mass Index (BMI). This is calculated as follows:
BMI = mass (kg)/ height (m)²

A person is considered obese when their BMI is greater than or equal to 30 kg/m². Overweight is regarded as a BMI between 25 and 29 kg/m².

BMI is regarded as a relatively good measure of body fat in most people except someone who is very heavily muscled. In this case, the BMI could be high, but the percentage of body fat low.

Other measures are often used in overweight or obese people to gauge the level of risk associated with their degree of overweight. The percentage body fat and the distribution of this fat are important and the waist-to-hip ratio is a simple method for determining a person’s distribution of body fat. This is determined by dividing the waist circumference by hip circumference. Waist circumference is defined as the smallest circumference between the rib cage and belly button. Hip circumference is defined as the largest circumference of the hip-buttocks region.

The table below relates BMI and waist-to-hip ratio with disease risk:

Waist-hip-ratio

BMI	Disease risk	Men	Women
22.00 to 24.99	Very low	Less than 0.85	Less than 0.80
25.00 to 29.99	Low	0.85 to 0.89	0.80 to 0.84
30.00 to 34.99	Moderate	0.90 to 0.99	0.85 to 0.95
35.00 to 39.99	High	1.00 to 1.10	0.96 to 1.05
40.00 and above	Very high	Greater than 1.10	Greater than 1.05

Since the development of obesity is deeply rooted in the enlargement of fat cells, a person’s percentage body fat is important. This is accurately measured using a series of skin-fold estimates from different parts of the body. Other techniques such as electrical impedance are far less accurate.

The table below shows body-fat norms based on the percentage of mass which consists of fat:

Percentage fat

Classification	Women	Men
Essential fat	13.0 - 14.0	3.0 - 5.0
Athletes	12.0 - 22.0	5.0 - 13.0
Acceptable	16.0 - 25.0	12.0 - 18.0
Potential risk	26.0 - 31.0	19.0 - 24.0
Obese	32.0 and higher	25.0 and higher

What causes obesity?

Simply put, obesity results when there is an imbalance between food eaten and energy expended. There are three components to energy expenditure:

“resting” energy expenditure

physical activity

 thermic effect of food

Resting energy expenditure is most strongly associated with fat-free body mass. The metabolic mixture used by the body is related to the types of food eaten, to the adaptive capacity of the body and the rate of energy expenditure. The maintenance of energy balance requires that the mix of foods eaten can be used by the body – oxidised.

It is difficult to store carbohydrates and protein. Only the fat stores can readily expand to accommodate increasing levels of food intake above those required for daily energy needs.

The amount of energy expended in physical activity is directly related to body weight. In most people, physical activity declines as they age and the vast majority find it difficult to maintain a regular exercise programme, particularly as they get older.

The thermic effect of food is the third component of energy expenditure. After eating, there is a rise in energy expenditure equivalent to about 10% of the day’s total energy expenditure. However, in very fat or obese people this effect is not as marked because of problems with insulin resistance which will be discussed later.

Obesity is a reflection of increased fat stores, in both the stores under the skin and in the rest of the body. Obese people have enlarged fat cells. The many chemicals made and secreted by these fat cells play an important role in the clinical consequences of obesity. The enzyme insulin plays an important role in the deposition and mobilisation of fat.

The detailed physiology and biochemistry of the development of obesity is now much better understood. This greater understanding is starting to contribute to the way in which obesity is treated.

Who is obese and what are the risk factors for developing obesity?

People can become overweight at any age, but it is more common at certain times.

Several surveys show that one third of overweight adults become overweight before the age of 20 and two thirds do so after that. This means that between 75% and 80% of adults will become overweight at some time in their lives.

Between 20 and 25% of the population will become overweight before the age of 20 and 50% will do so after the age of 20.

Some overweight individuals will develop clinically significant problems such as diabetes, hypertension, gallbladder disease or the metabolic syndrome. The latter is a syndrome (collection of symptoms and signs) which is characterised by resistance to insulin (the body cannot use insulin effectively), problems with glucose tolerance, abnormal levels of lipids (fats) in the body (dyslipidaemia), central obesity (fat around the midriff), problems with the blood which mean that thrombosis is more likely and increased uric acid levels. It is easy to see how the metabolic syndrome will lead to other clinical problems such as diabetes, hypertension and heart disease in general.

Obesity is on the increase in the Western world so it is important to understand the risk factors associated with developing obesity.

Risk factors associated with obesity

Overweight parents

 Lower socioeconomic status

  Stopping smoking

 Low level of physical activity

 Low metabolic rate

 Being overweight as a child

 Being a heavy baby

 Lack of maternal knowledge of a child’s sweet and cooldrink eating habits

 Recent marriage

 Having multiple births

 Eating an unbalanced diet rich in fat

Along with these risk factors there are other things to take into consideration when looking at the risks of becoming obese.

Body weight during adolescence is a good predictor of adult weight status. Overweight adolescents had a five to twenty-fold increased chance of being overweight as adults.

Most women gain weight after puberty, which may be precipitated by pregnancy, oral contraceptives and menopause.

Pregnancy itself may leave a legacy of increased weight with some women never regaining their pre-pregnancy weight.

Can obesity be prevented?

A population can be divided into four subgroups – never overweight, pre-overweight, preclinical overweight and clinically overweight.

The first – never overweight – are people who will never become overweight. The second group includes all people who have a BMI below 25 kg/m².

When someone becomes overweight without any medically significant problems, then they are pre-clinically overweight. As time goes on, these same people may develop the medical complications associated with obesity such as diabetes, hypertension, dyslipidaemia – once these are present they are then classified as clinically overweight.

Prevention strategies focus around these groupings. Pre-overweight and preclinically overweight people are assessed in terms of the risk factors outlined above. Those normal weight people who appear likely to become overweight should start measures such as a sensible, low-fat diet and a regular exercise programme to ensure that they do not gain weight.

People who are already overweight, but who do not yet have medical problems associated with this should be encouraged to lose weight through a sensible, low-fat eating plan and a regular exercise programme.

If these interventions are made early enough, and people stick to them, then obesity can be prevented.

How is obesity treated?

The basic idea behind treating obesity is simple – reduce energy intake and increase energy expenditure. However, to be successful this involves completely changing someone’s lifestyle – never easy for anyone.

It is important that the overweight or obese person understands the potential medical complications which can result from remaining overweight. This provides motivation for weight loss.

People should be encouraged to change their eating patterns in such a way that they can maintain these changes for life. Fad diets, slimming supplements and pseudo-scientific diet programmes are seldom successful in the long-term and can be positively harmful.

A diet that is high in complex carbohydrates, contains medium amounts of protein and low in fats – particularly saturated fats – will aid weight loss.

Exercise has a major role to play in aiding and maintaining weight loss. Very high intensity exercise – generally sport-specific training - will increase the rate of weight loss with an appropriate diet. However, this is not possible for most people since they are not prepared to go to these lengths. But there is plenty of evidence to show that moderate to low intensity exercise will also aid weight loss. What is more important is that regular exercise helps to maintain weight loss over time. All adults should be encouraged to exercise at moderate intensity for around 30 minutes on most days. This can be walking, swimming, jogging, cycling or any other activity that is enjoyable.

Changing from a generally sedentary lifestyle also helps. Parking the car further from the shops and using stairs instead of lifts are simple measures which can increase your daily energy expenditure.

Drugs are a last resort and should only be used for people whose BMI is more than 30 kg/m² and who have failed to lose weight through diet and exercise. Most of the drugs currently available to treat obesity are appetite suppressants which act on the central nervous system and are only approved for short-term use.

One drug which is approved for use for up to one year is sibutramine. The evidence is that people using this drug can achieve weight loss of up to 5 to 10% of their body weight. Its side effects include dry mouth, insomnia and constipation. It also produces a small increase in heart rate and a small rise in blood pressure. People using the drug should be carefully monitored by their doctor.

Orlistat is a drug which blocks the absorption of fat in the intestine. In clinical trials lasting up to two years, this drug was associated with an average weight loss of 10% at the end of one year in patients who were eating a diet which only contained 30% fat.

Effective use of either of these medications requires changes in lifestyle as well – there is always diet modification involved in weight loss, as well as an increase in physical activity if possible.

Surgery is reserved for those who suffer serious medical consequences of gross obesity and who cannot lose weight in any other way.

With any treatment it is important to know what your goals are and obesity is no different. For most people, weight rises with age, slowly and inexorably. The main preventative strategy would be to prevent further weight gain, which in itself would be beneficial in terms of preventing the medical complications of obesity and decreasing the incidence of this condition in the population. Weight loss of less than five percent is generally considered inadequate and weight loss of up to 12% is required to prevent the onset of type 2 diabetes in susceptible people.

An ideal outcome of treatment would be a return of body weight to the normal range with no further weight gain later. However, this is unrealistic for most people. A more realistic goal is usually between five and 15% of body weight and good maintenance of that weight loss. This would be a good outcome for which people should be congratulated.

An excellent outcome is weight loss of more than 15%. In practice it is difficult to achieve a weight loss of more than 15% for most patients.

An improved quality of life is also an important outcome which can take many forms. Any reduction in the medical complications of obesity, such as type 2 diabetes and hypertension will improve quality of life, not least because of the costs of treating these conditions. Weight loss also reduces the wear and tear on osteoarthritic joints and in some cases slows or reverses the development of osteoarthritis altogether.

A loss of five percent or more of initial weight almost always translates into improved mobility, increased ability to exercise and improved self-esteem.

What is the outcome of obesity?

The major consequences of obesity are the increased rates of death and disease associated with the condition.

Most of the medical complications of obesity result from increased production of fatty acids due to the enlargement of fat cells. Other consequences result from the increased mass of fat in the body.

It has been estimated that obesity is responsible for nearly 300 000 deaths each year. These excess deaths are usually due to heart disease, diabetes, hypertension and cancer.

Diseases which seem to be associated with enlarged fat cells and their metabolic products include type 2 diabetes, heart disease, hypertension, gallbladder disease and cancer.

Even small increases in BMI and the size of fat cells are associated with a significant increase in the risk of developing type 2 diabetes. It appears that the metabolic products of the fat cells place an increased demand on the pancreas for insulin. Weight loss of 12% or more which is then maintained seems to be able to restore the function of the pancreas to normal, underlining the importance of prevention and early treatment of obesity.

Increasing deaths from heart disease occur with increasing obesity in both men and women. This increase is most pronounced in people with BMIs greater than 27 to 29 kg/m². This increased risk can be attributed to a number of things. Levels of high-density lipoprotein (HDL) cholesterol ("good" cholesterol) decrease in the face of insulin resistance and obesity. There is also an increased concentration of a blood factor which prevents clotting within blood vessels. Increased blood pressure associated with obesity also plays a role in increased risk of heart disease. All these factors revert towards normal ranges with weight loss.

Blood pressure rises with increasing BMI, as does the risk of developing gallstone disease.

Cancer of the womb (endometrium), breast, colon and gallbladder is more common among obese women. Cancer of the prostate and colon are more common among obese men.

Sleep apnoea is a serious problem among overweight people and is more common in men than women. In this condition the airways are intermittently obstructed at night leading to fitful sleep and lack of oxygen. This leads to increased sleepiness during the day. The increased mass of fat in the pharyngeal (throat) area partly explains this complication of obesity.

Osteoarthritis eventually happens to us all, but is far more marked among overweight and obese people. In women in particular, damage to the knee and hip joints is severe in the overweight and obese. This is a potentially costly complication of obesity in terms of the misery caused by the damaged joints and the actual costs involved in replacing them if this becomes necessary.

One of the most damaging consequences of obesity is social disapproval and stigmatisation. Extra weight is obvious to everyone and fat people are generally characterised as being lazy and lacking self-control. Fat men and women suffer social stigmatisation which worsens their quality of life. Social stigmatisation is particularly severe in women, where social disapproval is one of the main pressures for weight loss. Some studies have even shown that fat people have more trouble getting employed, and when they are employed, they are paid less than their leaner counterparts.

When to see your doctor

If you are gaining weight and/or are overweight already, then see your doctor to discuss ways of preventing further weight gain and losing weight if necessary.