People often talk about being overweight, meaning that they have too much loose flesh around the abdomen (men), and around the abdomen, thighs and buttocks (women). However, your bodyweight is made up of a number of things; bone, muscle, fluids, body organs, fat and other tissues all contribute to your total weight. Take a sauna and you will lose weight because you sweat water, but this is not a permanent weight loss. Begin a weight training programme and your muscles will become sleek, firm and toned. This may be desirable, but because muscle weighs more than fat you may actually gain a few pounds. What we really mean when we say someone is overweight is that they have too much fat, which is possibly linked to flabby muscle.

Body fat occurs in different types. Essential body fat is found around the body organs and within the marrow in the centre of the bones. Women have more fat than men because they carry additional sex-specific fat which is important for a variety of hormonal functions. If the level of fat is reduced too much, as can be the case in young girls who diet excessively, for example, a woman’s periods will often stop due to the hormonal changes caused by the low body fat. The other type of fat is storage fat which is found beneath the skin and acts as a depot for energy. It is the storage fat which often becomes excessive.

In order to lose inches from the waistline we need to reduce the amount of body fat, while maintaining a healthy, balanced diet, but this must be coupled with exercise to tone and shape the muscles of the abdomen or they will remain flabby.

Obesity is simply an excessive amount of fat in the body. The World Health Organisation
(WHO) defines obesity in terms of body mass index or BMI, saying that a person with a BMI over 30 is obese (see table 5.1). BMI is calculated by dividing a person’s weight in kilograms (kg) by their height in metres squared (m2). So, for example, if you weigh 70 kg (155 lb) and are 1.82 m (6.0 ft) tall, your BMI is 70 divided by 1.82 squared (3.3) which is 21. Looking at table 5.1 we see that a BMI of 21 is within the normal weight section.

Although BMI is a useful measure, it does not take into account the ratio of lean tissue (muscle) to fat (adipose tissue). As a consequence, BMI values can overestimate body fat in athletes who are very muscular, and underestimate it in those who are frail or wasted, especially the elderly. For this reason age, sex, body type, and race (ethnicity), should also be considered.

From the point of view of cardiovascular risk factors especially, where the body fat is stored is important. Central obesity, where body fat is concentrated around the middle of the body, is more dangerous than general obesity where the fat is evenly distributed all over the body. This is because central obesity sees body fat stored around the organs (visceral fat) resulting in a ‘beer belly’ appearance. This type of fat can change the concentration of the hormone insulin in the blood and is an important factor in the development of diabetes. If excessive, central obesity is obvious, but clinically its presence is determined by waist measurement and waist-hip ratio. Central obesity is present when the waist measurement is greater than 102 cm (40 inches) in men and 88 cm (35 inches) in women, and the waist-hip ratio is greater than 0.9 and 0.85 for men and women respectively.

The rapid rise in obesity during the last 25 years is due to a combination of factors, the two most important being diet and lack of exercise (sedentary lifestyle). The consumption of energy- (calorie-) dense fast food has tripled in the Western world during the last quarter of the 20th century. A sedentary lifestyle fails to burn off these excessive calories, and it is both general activity as well as exercise which is important here. For example, the school run (driving children to school rather than encouraging them to walk) is thought to be a prime mover in the development of childhood obesity. That small walk to and from school may not seem much but, because it is regular, it is a vital amount of exercise in an otherwise predominantly sedentary Western world.

One of the main factors which assists in the control of an ideal bodyweight is the feeding control mechanism (FCM). This is situated within the brain in an area called the hypothalamus. The FCM controls bodyweight by matching the amount of energy obtained from food to the requirements of the body through activity. If the amount of energy going into the body is exactly equal to the amount going out, the bodyweight will remain constant. Individuals who are overweight tend to have lost the ability to match their energy requirements to their diet. Unless the FCM is re-set, long-term control of an ideal bodyweight is unlikely. One of the problems with crash diets is that although they lead to a short-term reduction in weight, because they restrict the amount of energy going in, the FCM tries to conserve energy and the ‘tick-over speed’ of the body (the ‘basal metabolic rate’) is slowed by as much as 45 per cent. This means that weight loss will slow down and a person can quickly lose motivation because they always desire more food than they are getting. When they stop the diet, the weight goes back on and we get a yo-yo effect of repeated weight loss and weight gain over a period of time. A more effective method of weight control is to combine good dietary habits with regular activity as this type of programme has been shown to re-set the FCM to the correct levels.

The energy taken into the body as food, and that expended during activity, is measured in calories, a measure of the heat a food would produce if it were burnt. One kilocalorie or Calorie (with a capital ‘C’) is the more common measure, and this is equivalent to 4.2 joules, the joule being the other measure of food energy seen on food packaging. Some of the main constituents of food are carbohydrate, a starchy or sugary material giving energy; fat, an energy store and protein, used to build the body tissues. All of these substances can be used by the body for energy, and so may be measured in Calories. Both carbohydrate and protein produce the same amount of energy. Fat is a more concentrated energy source, and can produce more than double the energy of the other two types of foods. This is why fat is used as an energy store, and reducing it in the diet is a good way to lose weight. Another source of energy is alcohol which has almost the same number of Calories as fat.