Does it matter?
Obesity, as defined by a body mass index (a measure of body fat based on height and weight) greater than 30, has major health implications. It has been estimated that it is responsible for more than 9,000 premature deaths each year in England alone and reduces life expectancy by an average of nine years.

Being overweight increases the risk of heart disease, stroke, diabetes, high blood pressure, colon cancer, gall-bladder disease and osteoarthritis, to name but a few. Equally important, though less well documented, are the psychological and social problems experienced by the obese.

Is obesity becoming more common?
Recent statistics show that obesity levels in England have tripled in the past 20 years. Around a fifth of men and a quarter of women are now obese, and between 1996 and 2001, the proportion of obese children aged between six and 15 rose by 3.5 per cent.

Why is this?
There are a few medical conditions that can lead to obesity, the most common being polycystic ovary syndrome, underactive thyroid (hypothyroidism) and Cushing's syndrome. These can be diagnosed with simple blood tests. Certain drugs can also produce marked weight gain, particularly steroids.

There is no doubt that some people have a genetic tendency towards being overweight, but obesity is not achieved by genetic predisposition alone. While a small percentage of obese people can cite their genetic make-up as a contributory factor, diet and exercise play a very important role in almost all obese people.

Diet
Dietary surveys in the UK suggest that calorie intake within the home is falling, but the number of meals and snacks eaten out has increased as disposable income has increased. In 2000, around 675 million restaurant meals were eaten in England, and in 2001, 2 billion fast-food meals were eaten. Meals and snacks eaten out tend to be higher in fat than those eaten at home, which means people have an increased intake of calories.

People are also snacking more than they used to. Industry surveys show that sales of confectionary and snacks rise year on year and that we are the biggest snackers in Europe. The consumption of fizzy drinks has doubled in the past 10 years, and while some of these are low-sugar brands, many more are very sugary and highly calorific. There is also evidence that portion sizes are significantly larger than they were 30 years ago, particularly when t comes to fast food. Who can resist the offer of a 'supersize' portion for only a small extra cost?

Alcohol consumption has also played its part, as all alcoholic drinks have a calorific value. Alcohol intake, particularly among women and young men, has increased significantly in the past decade.

It has been estimated that even if you have a daily intake of calories only 50-100 calories above your energy needs it can lead to a weight gain of between 5lbs and 10lbs in a year.

Exercise
Increasing exercise levels is considered to be as important as dietary restriction in the battle against obesity. The recommended exercise level for adults is 30 minutes of moderate intensity activity (such as brisk walking) on five days each week. For children, the recommendation is an hour a day. Surveys show that 60 per cent of women and 70 per cent of men do not achieve the recommended level of activity. Around half of all children are also getting less exercise than is ideal.

Perhaps more important is the lower level of activity in everyday life. Walking and cycling for short journeys have commonly been replaced by a car trip, more people are employed in sedentary occupations, and leisure time is often spent on sedentary pastimes such as watching TV, using a computer or playing and video games. Sport in schools is on the decline and a decreasing number of children play outdoors because of parental concerns about safety.

So where do you start?
It follows from the above, that a shift in the equation between calorie intake and expenditure is the key to weight control. It is important for people who are trying to lose weight to have a realistic goal and a realistic time-frame for achieving it.

Weight loss of 2lbs a week is ideal. If you lose more than this it is usually due to water loss in the initial stages, and muscle loss with prolonged dieting. Neither of these is healthy or desirable. Losing 2lbs of body fat a week is the recommended goal, and can be achieved with a relatively modest increase in activity and decrease in calorie intake. Weight loss of 22lbs (achievable in 11 weeks) in an obese person can produce major health benefits, so it isn't necessary to achieve an ideal weight in order to reduce health risk.

These issues are important to remember for those who are very obese and find it difficult to contemplate the long haul back to a healthy weight. It is easy to become demoralised if you are five stone overweight, and easy to feel that the goal is beyond your reach. I usually advise people to look away from the goal of 5 stone weight loss, and look towards the goal of 2lbs weight loss this week. Short-term goal-setting is much more likely to be successful and focuses on repeated achievement rather than on the length of the task ahead.

A policy of smaller portions, fewer snacks, less calories from sugary and fatty foods, less alcohol and a more active lifestyle will work for most people. Rigid diet plans hardly ever succeed, faddy eating plans never result in permanent weight loss, and the more flexible your eating plan is, the more likely you are to follow it. Try to have as much variety in your diet as possible because this prevents boredom from setting in and reduces that feeling of deprivation that is so depressing when trying to lose weight.

Weight-control groups help a lot of people to sustain the effort. The 'kindred spirit' aspect can be very helpful and the weekly weigh-in can be very motivating. The feeling of achievement when the numbers are getting smaller is great, even if the change is quite small. I know these things to be true because I've done it!

What about drugs?
At present, there are two drugs that are licensed for the treatment of obesity. Xenical acts by blocking the absorption of fat from the diet. It can be very useful, but only if taken in conjunction with a low-fat diet. Higher fat intakes result in unpleasant diarrhoeal side-effects. Reductil is a drug that acts on the brain to suppress appetite. It is only suitable for some people as it is a complex drug and can lead to many side-effects, including the possibility high blood pressure, so close monitoring is necessary.