In today's world, people tend to be judged by their appearance - especially when it comes to health. We often think someone who's slim is healthy, whereas someone with a large girth isn't. Recently, the second annual American Body Fat Perception poll found that most of those surveyed believed managing body weight and maintaining appearance were the most important criteria to being healthy and fit. Almost half (43 per cent) felt their body weight had a greater impact on their health than the percentage of body fat they carried, and more than half (52 per cent) said they didn't need to worry about body fat as long as they didn't appear fat. Until recently, most fitness experts believed health could only be achieved by attaining an 'ideal' weight or body mass index (BMI) - an estimate of body fat using weight and height. Today, this emphasis on thinness for health is slowly shifting to fitness. President of the Cooper Institute in Dallas, Dr Steven N. Blair, says focusing on an ideal weight or BMI is ridiculous. 'This is like saying people should be an ideal height or have an ideal eye colour - it's meaningless,' he says. 'Even with optimal diet and physical conditioning, there is vast variation in weight.' Blair was one of the first researchers to try to find out if one could be both fit and fat. In the 1990s he studied almost 22,000 men in the US aged from 30 to 83. All the study participants went through treadmill tests to measure their cardiovascular fitness levels, had their body fat levels measured and were given complete physical checks. Blair found that their fitness levels were much more important in predicting health and longevity than either body weight or BMI. A similar study published last month in the Journal of the American Medical Association came to similar conclusions regarding women's health. In this study of almost 10,000 women, physically fit subjects had a lower risk of developing cardiovascular disease, regardless of whether they were fat or thin. These moderately fit women of different weight ranges averaged 48 per cent lower risk of dying early than unfit women. And the fittest women had a lower risk of premature death than the thin, but unfit, women. While intriguing, these studies don't advocate being overweight as good for your health. High blood pressure is still twice as common in obese people as in people of normal weight. Also, gaining weight itself is a risk. According to the Yale Centre for Eating and Weight Disorders in Connecticut, gaining six to nine kilograms doubles the chance of developing Type II diabetes compared with people who maintain their normal weight. Women who gain more than 9kg between the ages of 18 and 40 double their risk of developing menopausal breast cancer, and for every kilogram of weight gain there is a 9-13 per cent rise in the chances of developing arthritis. What's the message in all this? To begin with, taking off excess weight can have an incredible impact on your health. Any sedentary person who starts to exercise on a regular basis, while maintaining the same diet, will drop weight. And while researchers still agree that the leaner and fitter we can be, the better, being healthy doesn't mean being pencil thin. According to Blair, 'thinness may not always be attainable - especially the extremely slim promulgated by Hollywood - but nearly everyone can become fitter'. And between fitness and thinness, fitness seems to contribute greater to a long and healthy life.