What is obesity? And where will you find it?

How fat is fat?

	Someone is obese if they have a very high amount of body fat in relation to lean body mass. Scientifically, obesity is defined by the Body Mass Index, which is a measure of an adult's weight in relation to his or her height¹. Above 25 is overweight, above 30 is obese.

A number of factors can influence the onset of obesity. Most directly, weight gain is caused by an energy imbalance between calories consumed and effort expended. We generate around 1lb of fat for every 3500 body calories gained.

Body mass is also influenced by other factors such as our genes, metabolism, behaviour, environment and culture, any of which may increase our risk of gaining weight. And the increase is alarming.

It's not just in the industrialised countries where obesity has risen at an epidemic rate. The UN has found obesity in all developing regions. Figures for the developing countries point to in excess of 115 million people, in an environment where obesity often masks underlying deficiencies in vitamins and minerals.

In China, a first comprehensive population weight survey in 2002 classified 22.8% of the population as overweight, and 7 % as obese. A study conducted by the Centre for Obesity research in Kanpur counted 39 million Indians with obesity in 2000. In October last year, the International Association of the Study of Obesity held its first conference in South Africa, a reflection of the growing problem of obesity in the region, quantified in 1998 as 29% of men and 56% of women overweight or obese.

Environmental changes such as easy access to cheaper processed foods have clearly had an impact. High sugars and fats have replaced traditional diets of grains and vegetables. Even in countries such as Japan, famed for its healthy diet, the incidence of obesity is rising dramatically.

¹ Weight in kilograms divided by the square of height in metres