BMI this… BMI that… Well, body mass index (BMI), is arguably the most popular and definitely, the most thrown-about term in fitness circles. Many take it as an absolute indicator of fitness. It is calculated by taking into account the height and weight of the person. While it gives you a parameter for what the ideal weight of a person should be with respect to their height, it is not a very accurate indicator of health and has several limitations, say experts.
What is BMI?
“The formula to calculate the BMI (body mass index) involves taking the weight in kilograms and dividing it by the square of the height of the person in meters,” says Ashish Paurana, a Bengaluru-based weight-loss management specialist.
The number obtained gives an idea of whether you are underweight, normal weight, overweight or obese.
“When the BMI is anything less than 18.5 then you are underweight,” says Dr. Nasiruddin G, consultant internal medicine, Fortis Hospital, Bangalore. “If it is between 18.5 to 24.99 then you fall in the normal range and above 25 is overweight. Pre-obese is anything between 25 to 29.99, and obese is anything more than 30.”
Limitations of BMI
BMI provides the ideal weight range for different heights and can be used as a basic indicator of your weight status. But here are some limitations of BMI.
- One formula for all: “Adult BMI calculator is used for people more than 20 years of age. And for people aged less than that, we cannot really use it,” says Dr Nasiruddin. Moreover, the formula is used for all and does not take into consideration the age and gender of the person which are big variables as far as fitness and body composition are concerned.
- Lacks body composition details: “It does not give you details about the body composition such as muscle mass, bone density, water content, fat percentage and distribution,” says Paurana.
- Not an accurate indicator of health: The classification of BMI helps in assessing the risk of hypertension, diabetes, cancer, high cholesterol and other chronic disease. However, it cannot be assumed that people who fall within the ‘normal’ weight range will not have health risks nor that two people with the same BMI will have the same health risks. “A person with high muscle mass can have the same BMI as another person with high body fat. The [health] risks will be different in these two,” adds Dr Nasiruddin.
- Cannot be used for athletes and hardcore fitness enthusiasts: With BMI being a tentative indicator of body fat, people with a high BMI are assumed to have a high-fat content. This may not always be true. “For instance, in the case of athletes, sportspersons and hardcore fitness enthusiasts, they might end up on the heavier (overweight and obese) side of the BMI chart. This could be because of high muscle mass and not high-fat content,” says Paurana.
Alternate ways to measure health
Since BMI has its limitations, it should be used only to keep a basic tab on weight. Other popular ways to measure health or fitness levels include measuring the WHR (waist-hip ratio) using body composition analyzer machines. Routine health checkups are a great way to keep a tab too.
Hip-waist Ratio: To calculate the waist-hip ratio, you must divide the circumference of the waist by the circumference of the hip. This gives you an indication of the amount of abdominal fat present.
“The abdominal fat poses greater health risks than the fat stored in other parts of the body,” says Dr Nasiruddin. “The waist-hip ratio indicates the risk of developing some serious health condition. The risk is high when the ratio is greater than 1 in men and greater than 0.85 in women, the risk is moderate when the ratio lies between 0.9 to 1 in men and 0.8 to 0.85 in women. The risk is low when the ratio is less than 0.9 in men and less than 0.8 in women. In our practice, waist-hip ratio has shown to be a better predictor of cardiovascular diseases than body mass index.”
Body composition analyzer machines: These machines are found in gyms and health care centers. “It not only considers your height and weight but gives much more information on the fat content present, its distribution, the muscle mass, bone density, water content, etc. This makes it easier to understand the health risks associated as well,” explains Paurana.
- BMI is a calculation done by taking the height and weight of the person into consideration. It gives information about what the ideal weight should be with respect to height.
- There are many limitations to BMI calculation such as, it does not take gender and age into account. It does not give information about body mass composition and cannot be used for athletes, sportspersons or people with certain conditions.
- Waist-hip ratio, body composition analyzers and routine general checkups are other popular means to measure health or fitness.