Body mass index (BMI) is a measurement that uses your height and weight to determine if your weight is healthy.
The BMI calculation divides an adult's weight in kilograms by their height in meters squared. For example, a BMI of 25 means 25 kg/m2.
BMI ranges.
For most adults, an ideal BMI is in the range of 18.5 to 24.9. For children and youth ages 2 to 18, the BMI calculation takes into account age and gender, as well as height and weight.
If your BMI is:
Below 18.5: you are in the underweight range.
Between 18.5 and 24.9: you are in the healthy weight range.
Between 25 and 29.9: you are in the overweight range.
30 or more: you are in the obese range.
If you want to calculate your BMI, you can use the healthy weight calculator.
BMI accuracy.
The BMI takes into account natural variations in body shape, giving a healthy weight range for a particular height.
In addition to measuring your BMI, health professionals may take other factors into account when assessing whether you are at a healthy weight.
Muscle is much denser than fat, so very muscular people, such as heavyweight boxers, weight trainers, and athletes, can still be at a healthy weight even though their BMI is classified as obese.
Your ethnic group can also affect your risk for some health conditions. For example, adults of South Asian origin may be at higher risk for some health problems, such as diabetes, with a BMI of 23, which is generally considered healthy.
You should not use BMI as a measure if you are pregnant. Ask your midwife or GP for advice if you are concerned about your weight.
Clinical relevance of BMI.
BMI is an indicator of total body fat in many people. Therefore, it is considered an indicator of health risk. Health professionals use BMI to detect people who are overweight or obese. The BMI is used to assess a person's health risks associated with obesity and being overweight.
For example, those with a high BMI are at risk of:-
· High blood cholesterol or other lipid disorders.
· Type 2 diabetes.
· Heart disease.
· Stroke.
· Hypertension.
· Certain types of cancer.
· Gallbladder disease.
· Sleep apnea and snoring.
· Early death.
· Osteoarthritis and joint disease.
BMI, however, is one of the tools used to calculate healthy risk. Other factors such as blood pressure, cholesterol level, blood sugar level, family history of heart disease, age, gender, waist circumference, level of physical activity, menopausal status, smoking, etc. are also taken into account when assessing the health risk.
Does the BMI apply to everyone?
For most people, the BMI can be used to provide a good measure of obesity. But BMI doesn't give you real information about body composition, such as the amount of muscle, bone, fat, and other tissue.
For some people, BMI is a more accurate measure of body fat than for others. For example, very muscular people may fall into the “overweight” category when they are healthy and physically fit. These people with a very low percentage of body fat could have the same BMI as someone who is overweight.
Similarly, an elderly and frail person may be in the normal weight category when they have low muscle mass and a high percentage of body fat.
BMI, when used for children and adolescents who are still growing, those with large body frames or small builds, pregnant women, and very muscular individuals, therefore should be carefully evaluated and interpreted.
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