The epidemics of obesity and Type II, or late-onset diabetes, are rising in parallel, driven by modern lifestyles. A diet of fast foods, high in fats and calories, eaten by people who take the car rather than walk is to blame.

One of the most alarming features is the growing number of children affected. Specialists report increasing numbers of overweight teenagers turning up in diabetes clinics with a disease that a generation ago was confined to people over 40.

They face a lifetime of treatment, and can expect symptoms including eye damage, circulatory problems and kidney failure to worsen as they age. A study by the International Obesity Task Force in the British Medical Journal suggested 1,400 children in the UK have full-blown type II diabetes and up to 20,000 have impaired glucose tolerance, where the body loses its capacity to use sugar, which foreshadows diabetes.

Diabetes causes blood-sugar levels to rise because of a lack of insulin. Raised sugar levels lead to high blood pressure, increasing the risk of heart attack, stroke, blindness caused by retinopathy, kidney damage and ulceration of the feet, which can lead to amputation.

Type II diabetes can be treated by diet and exercise and the effects are reversible if the damage has not gone too far. In more severe cases, drug treatment - tablets or insulin injection - is necessary. Men and women are equally likely to get the disease but women are more likely to die earlier. The affliction is directly linked to obesity, measured in body mass index, a combined measure of height and weight. A person with a BMI over 35 is up to 80 times more likely to develop diabetes over 10 years than someone with a BMI of less than 22. In its early stages, the condition may cause few symptoms and go unrecognised. Common signs are increased thirst combined with increased urination as the body tries to rid itself of excess sugar, weight loss and recurrent infections.

One in 30 of the adult population has diabetes but experts estimate one in five has metabolic syndrome, a precursor of diabetes, which raises their risk of developing the full-blown condition up to five-fold.

The main indicator of metabolic syndrome is a large belly. A waist measurement more than 94cm (37 inches) for men and over 80cm (31.5 inches) for women should be the trigger for tests of blood pressure, fat levels and glucose in the blood. Those affected can then be advised on action to take. "Eat less and walk more is the advice I give," Professor Sir George Alberti said.

n BMI is calculated by dividing the patient's weight in kilograms by the square of height in metres. A BMI showing normal weight is 18.5 to 24. People with a BMI of 25 to 29 are overweight and above 30, obese. A person of average height - 5ft 8in (173cm) - weighing less than 8st 10lbs (55.5kg) is underweight. Up to 11st 9lbs is normal. Overweight is between 11st 9lbs and 13st 11lbs. Above is obese. A BMI above 35 - 16st 5lbs - is "extremely obese".