What is BMI?
BMI or body mass index is a value used to determine whether a person has a healthy weight in relation to his or her height. It can be calculated as body mass divided by the square of height and is expressed in kg/m2.
How is BMI used?
BMI is used to assess whether or not a person’s weight is appropriate for his or her height, i.e., whether or not he or she is at a healthy weight. There are four main categories to which a person can belong:
- Underweight
- Normal weight
- Overweight
- Obese
These categories can be subdivided to assess the degree to which a person is underweight or obese.
BMI or body mass index is a value used to determine whether a person is at a healthy weight in relation to his or her height.
If a person’s BMI is particularly low or high, he or she may be advised to make lifestyle changes or even receive treatment if the doctor believes his or her weight is affecting his or her health.
Patients with high BMIs are at increased risk for a number of serious conditions, such as coronary artery disease, hypertension and stroke; while people with low BMIs may suffer from malnutrition or an eating disorder.
What is a healthy BMI?
A BMI of 18.5-25 kg/m2 is considered a healthy weight for an adult, according to WHO (World Health Organization) guidelines.
A BMI between 25 and 30 is considered overweight, while those with a BMI over 30 are considered obese. Obesity can be classified as moderate (BMI 30-35), severe (BMI 35-40), very severe (BMI 40-45), morbid (45-50), super (BMI 50-60) and hyperobesity (BMI 60+).
BMI is used differently for children. Instead of categorizing them according to fixed thresholds, children’s BMI is compared to percentiles for age groups and genders. Those with a BMI below the 5th percentile are classified as underweight children and those with a BMI between the 85th and 95th percentile as overweight.
Thresholds for adults differ in some Asian countries.
Limitations of BMI
Although BMI is considered a fairly reliable indicator of whether an individual is at a healthy weight, there are certain limitations:
- It does not distinguish between fat and muscle – muscle tissue is heavy, so a healthy individual with a high muscle mass may be “overweight” according to their BMI.
- It does not take into account physical characteristics such as body structure – thin individuals may have a lower ideal weight compared to someone of the same height with a stockier build.
- Some people argue that because BMI uses the square of height rather than the third power, it produces unfair and inaccurate results for particularly short or tall people.