Obesity has become one of the most serious medical problems of the western world.

Obesity is excess body fat for a given height and gender. It happens when more calories are taken into the body than are burnt up in a given period of time.

Once adulthood is reached, everyone has a fairly steady rate of calorie burn-up, called the metabolic rate. This is higher in people who are regularly physically active. This means that someone who works in a very physical job, such as a building-site labourer, may need as many as 4000-5000 calories per day to keep an even weight. This contrasts with an office worker who uses a car and doesn't exercise, who may need only 1500 calories per day.

If calories in food energy are greater than the calories used every day, the body stores the excess energy as fat - DI=T (daily intake equals turnout).

This is important as a protection for the body against times of starvation. In developed countries, starvation is rare except in extreme circumstances, so this insurance against hard times is hardly ever needed. Food is plentiful, and a lot of available food is much higher in calories than the human body was originally designed to cope with. The result is that eating more than the body needs is easy.

Obesity can be measured in different ways:

•	An easy way is just to get on the scales and compare your actual weight with your ideal weight. Any calorie-counting book will give this information.
•	A more scientific way is to calculate your Body Mass Index (BMI). This is your weight in kilograms divided by the square of your height in metres. In England, people with a body mass index between 25 and 30 are categorised as overweight, and those with an index above 30 are categorised as obese.
•	Modern gyms and some weighing scales can electronically measure the percentage of your body weight that is fat, and can compare this with what would be ideal for you.

Tim, Aged 37

“I decided to try the Traffic Light Diet after my weight had crept up to 16 stone. I have to admit to being very sceptical because I have tried so many different things to lose weight, and got bored with most of them. Within 6 months I had lost 3 stone, using the Traffic Light Diet, along with a controlled exercise plan. The colour-coded fridge magnet system was fantastic, as I could see what I could eat daily and how many units I was using. This allowed a variety of healthy foods in my daily diet, and I could do away with boring set meals, pills and powders offered by so many other diets. I have stayed at a constant weight for the last 6 months, and feel healthier and fitter. I would recommend the Traffic Light Diet to anyone who really wants to lose weight.”