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Obesity is a growing health problem in the UK. Currently, over half of the adult population is overweight, with 17% of men and 21% of women being classified as obese.

However, in general, the public view obesity more as an aesthetic problem than as the serious health problem it is. The fact is, excess weight is a major risk factor for premature death, cardiovascular disease, type II diabetes, certain cancers and other chronic health problems. Despite this, obesity rates continue to rise.


Obesity is defined as an accumulation of body fat. Although it would be better to assess body composition, the simpler calculation of body mass index (BMI) is more commonly used. BMI is a marker for obesity and is calculated by dividing an individual's weight (in kilograms) by the square of their height (in metres).BMI does not account for the distribution of body fat, which may differ between race, gender and age. For instance, excess fat stored around the abdomen - central obesity (apple shaped) - is more commonly associated with health risks, such as diabetes and cardiovascular disease, than fat stored elsewhere. Measurement of BMI may also give misleading results for individuals who are unusual in body composition, for example athletes who have a large proportion of muscle.

Causes of obesity

A great deal of scientific study has been undertaken in an attempt to understand why some people become over-weight and obese. Researchers have also tried to devise the best methods to lose weight and to assess the affects of weight loss on health.

Maintenance of energy balance is dependent both on energy intake and energy expenditure. If energy intake from food and drink exceeds the amount used for physical activity and bodily functions, the excess is stored as body fat, resulting in weight gain. The optimal combination to avoid positive energy balance and obesity is a low-fat, high-carbohydrate diet and regular physical activity.

There is an increasing realisation that the emerging epidemic of obesity cannot simply be attributed to dietary factors. One of the clearest indications to support this is the fact that, in general, energy intakes are declining while average body weight is increasing. This indicates that physical activity levels are probably declining even faster, possibly as a consequence of increasing mechanisation and transport use.

Avoiding weight gain

The balance of the available evidence suggests very strongly that eating a diet that contains a high proportion of fat encourages an increase in body fat stores (Bray and Popkin1998; Astrup 2001).This effect is probably mainly attributable to the high energy density of such diets (Poppitt 1995) and the tendency of such diets to lead to a greater energy consumption before satiation. Individuals who do little physical work or exercise seem to be particularly likely to gain weight on a high-fat diet (Stubbs et al.1995). Conversely, a diet that is high in carbohydrate (and low in fat) seems to offer some protection against weight gain (Astrup 2001a). Since this style of diet (high carbohydrate/low fat, especially low in saturated fat) is recommended for general health, especially cardiovascular health (Yu Poth et al. 1999; American Heart Association 2002), it is now regarded as the most suitable diet for most people (Astrup 2001b).

The few studies that have compared sugar with other carbohydrate foods and drinks have not shown any differences between the different carbohydrate sources. All seem to offer some protection against weight gain (Food and Agriculture Organization 1998; Health Council of the Netherlands 2001). This protection does not seem to require the subjects to consciously limit their calorie intake (Astrup, 2000).

Studies of different population groups have shown that leaner people tend to consume more sugar and less fat than those who are fatter (Bolton-Smith and Woodward 1994; Hill and Prentice 1995). Interestingly, these leaner people also seem to have higher overall food consumption, suggesting that they are more active (Bolton Smith and Woodward 1994). However, these studies cannot show why the higher fat consumers are fatter, despite a lower total food energy intake, but it seems reasonable to assume that it is because they are less active than the others.

Losing weight

The basic rule for losing body weight is simple: take in fewer calories in food and drink than you expend. In practice, this is extremely difficult to achieve and maintain for the long periods of time that may be necessary. Weight loss that is too rapid may cause serious health problems, so it is generally recommended that slimmers should aim to lose no more than 1kg (2lb) per week. A reasonable target is to try to lose 1kg every 2 weeks.

Research has shown that reducing the proportion of fat in the diet leads to weight loss, even when energy intake is not consciously restricted (Astrup et al. 2000; Saris et al. 2000).

Provided substantial reductions in fat intake are not made abruptly, and subjects are not forced to eat above appetite, this has no adverse affects (Astrup 2001; Parks and Hellerstein 2000). Participation in some form of exercise seems to be a key element of successful weight loss programmes, and of attempts to avoid putting the weight back on (Miller et al. 1997). Visit Successful Dieting for more information.

Physical activity

There is a growing body of evidence that shows physical inactivity to be a better predictor of obesity than measures of diet quantity or quality. Furthermore, research shows us that people who are overweight but fit, have a lower risk from dying from all causes, including heart disease, than people who are unfit but a healthy weight.

Exercise is also important in the treatment of people who are already obese and has a particularly useful role in the long-term maintenance of any weight loss. Physical activity is associated with improved motivation and therefore with better dietary compliance, increased lean body mass, and an amelioration of the usual suppression of metabolic rate which accompanies weight loss.

Participation in some form of exercise seems to be a key element of successful weight loss programmes, and of attempts to avoid putting the weight back on. The first step for people who are obese is simply to modify their lifestyle to build in more physical activity. Simply moving around is difficult for someone who is very obese, but expends a lot of energy. Simple lifestyle changes are about becoming less sedentary, so include advice to decrease the amount of time spent watching television, surfing the internet, and playing computer games. The next stage is to become more active, for example taking the stairs instead of the lift/escalator, parking further away from the shops, getting off the bus a stop earlier, or walking to the shops. The aim is to gradually build up to 30-40 minutes of sustained exercise, such as brisk walking, cycling or swimming, at least five days a week.

The role of sugar

Adherence to a low fat diet can be difficult because fat is so important in the flavour of foods. Research has shown that the incorporation of sugar within the carbohydrate component of a weight maintenance diet (Saris et al. 2000) or, particularly of a calorie-reduced slimming diet (West and de Looy 2001) can help compliance with these diets by improving palatability without noticeably reducing their effectiveness.

Health benefits of weight loss

Weight loss in overweight and obese individuals improves the physical, metabolic, hormonal and psychological complications. Losing weight can eliminate some of the health complications and improve an individual's quality of life. A weight loss of up to 10 kg is a realistic target and will lead to several health benefits.


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Eating a healthy, balanced diet along with taking regular exercise is key to physical and mental wellbeing.

No foods should be considered as ‘good or bad’ as all foods play an important role in the diet. It is only when foods are eaten in excess that health problems result.

Read more about eating healthy