BMI (Body Mass Index)

BMI (Body Mass Index) is calculated by dividing a person's body weight [in kg] by the square of their height [in m]:

BMI [kg/m²] = (weight in kg) /(height in m)²

BMI has become an international indicator of overweight as it is easy to calculate and is currently one of the best indirect Methods for calculating fat mass.

Carrying excess weight is not an illness in itself, but is has been proven that being overweight results in a clear risk of developing Accompanying and secondary diseases.

To support the individual efforts of preventive behaviour it is possible to set Goal values for this parameter.

If overweight exceeds a certain level it is known as obesity, which is classified as a disease.

The following categories are given for adults in the WHO guidelines [WHO 2000]:

BMI is also influenced by build and muscle mass. So, for example, inaccurate figures will be obtained for people

• with above average muscle mass (e.g. sportsmen and women)
• who suffer from muscular dystrophy (muscle wastage) or
• who suffer from a water balance dysfunction (e.g. dehydration or oedema).

Consequently: BMI as the sole criterion indicating overweight and obesity is only informative up to a certain point!

Moreover, the BMI is modified depending on age. It was discovered, that there is not only a slightly higher BMI with increasing age [Mensink 2005] on the average of population. Also there is a change in the protective value of BMI at high age: While in younger years a low BMI stands for a higher life expectancy, it is a moderate increase of BMI in higher years [Stevens 1998]. Our Overview of the classification areas used by the GMON deals with these general limits.

• A moderate increase in BMI as one gets older is not critical. Firstly, BMI increases if there is a slight loss of weight without there being any changes in body composition (Example calculation of BMI if there is a reduction in height) [Sorkin 1999]. Secondly, moderate excess weight for older people can to all intents and purposes represent an advantage as a weapon against illness and disease.
• BMI guideline values for children and young people have been calculated in recent years as there has been an increased incidence of overweight and obesity among children.

To valuate the BMI it is common in Asia also to follow the recommendations of the societies JASSO (Japan Society for the Study of Obesity) and AOASO (Asia-Oceania Assiciation for the Study of Obesity). The limits in JASSO are equal to the WHO recommendations except the classification „Overweight" which is already called „Obesity" from 25 kg/m² up:

According to the body fat valuation AOASO defines lower limits [Nishida 2004]; Please see Overview of the Asian classification areas used by the GMON.

In spite of all potential influencing variables, if BMI goes outside the normal range then regular medical check-ups are recommended to prevent the risk of becoming overweight.

Underweight as a health risk should also be taken seriously and requires medical advice particularly if there is a tendency towards weight loss!

Refer:

Overview of the classification areas used by the GMON

Overview of the Asian classification areas used by the GMON

BMI guideline values for children and young people

Underweight as a health risk

Methods for calculating fat mass

Example calculation of BMI if there is a reduction in height