Adolphe Quetelet, a Belgian scientist, was the developer of the ‘Quetelet Index’, which we know today as BMI (Body Mass Index). The calculation is done using a person’s weight and height to arrive at a BMI index (number) to measure their body fat. The BMI number assists physicians in diagnosing health problems that may be weight related. However, BMI should not be used as the only tool to determine if a person’s weight poses a health risk. A skinfold thickness test should also be carried out and, before making a final assessment, the physician should take the patient’s medical history, family history, diet and level of activity into account.
The formula for calculating BMI is:
METRIC: The person’s body weight in kilograms divided by the height in meters, squared.
IMPERIAL: The person’s body weight in pounds divided by the height in inches, squared.
Having arrived at the BMI number, using the above formula with weight and height, the following was established:
Below 18.5 – underweight.
18.5 – 24.9 – normal.
25.0 – 29.9 – overweight
30.0 and above – obese.
The international classification of underweight, overweight and obesity, according to BMI, is clearly shown by the WHO (World Health Organization). The World Health Organization has used BMI since the 1980s to observe obesity, as well as underweight conditions such as anorexia nervosa and bulimia nervosa. Symptoms of these eating disorders are explained in more detail later in this article.
Due to the fact that the BMI calculation uses weight and height, it is popular way to determine if a person is overweight or obese. It is an inexpensive and easy method to establish a person’s weight status in comparison to those of the general public.
A 1994 survey carried out in America using the BMI calculation revealed that 49% of women and 59% of men had a body mass of more than 25. This clearly indicates that more than half of population had weight problems. Four percent of women, and two percent of men, in the same study, had a BMI of more than 40 which is considered to be morbidly obese. Another survey, conducted in 2007, revealed that 63% of Americans were overweight, with 26% being in the morbidly obese category. This shows an alarming increase in weight problems over a 13-year period.
On the other side of the coin, a BMI of 15 indicates that a person is suffering with starvation, while someone with a BMI of 17.5 is considered to have a serious eating disorder, e.g. anorexia nervosa, or bulimia nervosa. Anorexia nervosa is an eating disorder that, due to psychological dysfunction, causes the patient to believe they are overweight. People suffering with anorexia nervosa will starve themselves and even use diet drugs in an effort to prevent weight gain. This obsessive fear of gaining weight can often lead to death.
Unlike the sufferer of anorexia nervosa who endeavours to avoid food completely, the person with bulimia nervosa will have repeated episodes of binge eating, followed by self-induced vomiting. During the episodes of binge eating, there is a complete lack of control of how much, or what, they are eating. The abuse of laxatives and diuretics goes hand-in-hand with bulimia nervosa .
When calculating a BMI for children, it should be remembered that the criteria differs from adults. A child’s body fat will vary, depending on their age. In addition, boys and girls have different levels of body fat, especially during puberty. So, bearing this in mind, BMI in children and teens is age and sex related. The child’s individual bone and muscle density should be taken into account when calculating a BMI.
It must be pointed out that BMI is calculated by weight and height, and some people, for example athletes, may show a high BMI because their weight is made up of fat and muscle. In such cases, the BMI calculation does not reveal the accurate amount of body fat. The BMI calculation is high because of the increased muscle content, and therefore weight problems are unlikely. It must also be pointed out that weight is just one factor when establishing that a person is at risk of a disease. Other factors that should be taken into account are diabetes, hypertension, heart disease, cancer, stroke, high levels of cholesterol, gall bladder problems, osteoarthritis, sleep apnea and other respiratory conditions.
In addition abdominal fat, in the form of a person’s waist measurement, is considered to be health risk. Physical activity, or lack of it, must also be taken into account. A person who is overweight but does not carry excess weight around the waist has a much lower risk of developing an obesity-related disease. However, they must ensure that they do not put on any extra weight.