Most sources agree that the human body requires a certain amount of fat for good health. Fat helps regulate body temperature, stores energy, and cushions and insulates organs. The percentage of body weight that makes up this “essential fat” is around 4% of body weight for men and 10% for women. Beyond that, there’s a somewhat wide range of what is considered a healthy percentage of body fat.
The American Dietetic Association recommends that men have 15-18% body fat and women have 20-25% body fat. Healthy male athletes might be as low as 5-12% body fat, and healthy female athletes could be as low as 10-20%.
Body Mass Index was invented by Belgian polymath Adolphe Quetelet in the eighteen hundreds and is a measure of your weight relative to your height that estimates overall body composition. Doctors increasingly use the Body Mass Index (BMI), not body fat measurements, to determine whether or not a person is overweight.
While BMI is a reliable indicator of total body fat, which is related to the risk of disease and death it does have some limits. It (I was going to use the word “may” here but instead will use “does”) does overestimate body fat in athletes and others who have a muscular build. I have, at the time of writing 11% bodyfat but a BMI of 24.5. According to the BMI this is on the high side of normal, 1 more point and I’d be classified as over weight! It may underestimate body fat in older persons and others who have lost muscle mass.
The basic problem, especially in athletes, is that muscle is denser than fat. Some professional athletes are “overweight” or “obese” according to their BMI – unless the number at which they are considered “overweight” or “obese” is adjusted upward in some modified version of the calculation. In children and the elderly, differences in bone density and, thus, in the proportion of bone to total weight can mean the number at which these people are considered underweight should be adjusted downward.
While BMI was originally intended as a broad indicator of general health, it has now become a standard diagnostic tool of heart disease risk but may not be such an accurate indicator as it lumps muscle and fat into one category.
A study carried out by researchers at the London School of Hygiene and Tropical Medicine concluded, after analyzing data on 15,000 patients, that BMI is not a good indicator of health risks for elderly people. They favour a calculation which looks at hip-waist ratio.
Other researchers agree and suggest that in a comparative study of BMI, waist-to-hip ratio, waist measure and hip measure, waist-to-hip was the best predictor of heart attack risk and BMI should be disregarded as a clinical and epidemiological measure of cardiovascular risk.
As the researchers point out according to BMI calculations the whole of the English national rugby team would be classed as very-overweight to obese and at high risk of cardiovascular disease along with many other sportsmen.
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