Reasons why your BMI is wrong- BMI will classify him obese
The WWE superstar, Stone Cold Steve Austin was at the time 6ft 2ins in height and 114kg (252lbs) in weight, but when calculated, his BMI will be 32.4 meaning he is classified obese.
Experts say at least 75 million U.S adults are wrongly classified when BMI is used as the health yard stick, study reported in the International Journal of Obesity and led by A. Janet Tomiyama, assistant professor of psychology, University of California-Los Angeles (UCLA).
54 million Americans classified as overweight and obese according to their BMI are healthy and 21 million classified healthy based on their BMI are actually unhealthy as shown by cardiometabolic measures.
What is BMI?
BMI refers to “body mass index” and it is used to determine if a person is overweight obese or normal weight. This is based on the height and weight of the person. BMI = weight in kilograms divided by height in meters squared. Using the BMI, your weight is classified according to these BMI ranges;
· 18.5 and 25, – normal weight,
· 25 and 30 – overweight,
· 30 and above – obese.
Did you know that?
Your muscle weighs more than your fat?
· A cubic inch of muscle weighs more than a cubic inch of fat.
· Muscle is denser than fat.
BMI does not take into account your body fat versus muscle or lean tissue content
But here is the problem, experts say BMI does not take into account your body fat versus muscle content, hence BMI will falsely classify muscular athletes as fatter than they really are.
The BMI calculation for a sprinter measuring 6ft in height and weight of 90kg (200lbs) compared to a person with a sedentary life style with the same height (6ft) and weight- 90kg (200lbs) will be 26 meaning that they are both over weight.
The experts say this classification for the athlete is wrong, but likely true for a person with a sedentary life style.
Here is why BMI should not be the yard stick
1. Experts say it does not measure body fat content correctly and does not take into account your muscle mass, bone density, overall body composition, as well as racial and sex differences. (The Perelman School of Medicine, University of Pennsylvania).
2. 34.4 million Americans classified overweight by BMI measurement are found to be healthy using cardiometabolic measures. The cardiometabolic health data used, measures blood pressure, triglycerides, cholesterol, glucose, insulin resistance and the marker of inflammation known as C-reactive protein.
3. In a study on patients survival rate after surgery, Patients with a BMI of 23.1 or less, were more than twice as likely to die within 30 days of surgery than those with a BMI of 35.3 or more.
4. BMI escalate thinness in short people and fatness in tall people.
5. Waist size has been linked to diabetes risk, regardless of BMI. According to research waist circumference is highly and independently connected to type two diabetes risk, even after accounting for BMI. The experts say that a non-obese, overweight male or female with a waist circumference of 40.2 inches (102cm) and 34.6 inches (88cm) or more respectively, faces similar or higher risk of type 2 diabetes as an obese male or female. The team recommends waist circumference for estimating type 2 diabetes risk and should be measure more widely.(Reported in PLoS Medicine by Medical Research Council (MRC) Epidemiology Unit, UK Study leader, Dr Claudia Langenberg).
6. The higher rate of diabetes seen amongst people in some countries is attributed to having much fat around their middle sections. The experts say “Americans carry more fat around their middle sections hence the higher rate of diabetes evident especially among American women. Hence waist size was referred to as the missing new risk factor that needs to be studied. (Study published by the RAND Corporation).
7. These experts recommend waist-to-height ratio to be considered as a screening tool instead of BMI, because BMI does not take into account the distribution of fat around the body despite the fact that abdominal fat affects organs like the kidney, liver and heart more severely than fat around the bottom or hips. Waist circumference gives an indication of abdominal fat levels.
Why the waist-to-height ratio as a screening tool?
§ Waist circumference gives an indication of abdominal fat levels.
· A waist circumference that is less than half your height can aid increase in life expectancy in every individuals across the globe.
· Using waist-to-height ratio, a 6ft-tall man should have a waist circumference of 36 inches or less, while a 5ft 4in woman’s waist should not exceed 32 inches.
· Your waist circumference should be less than half your height.(Dr Margaret Ashwell, consultant/ ex-director of the British science and Nutrition Foundation).
In the comparison between the 100m athlete and the person with a sedentary life style, the athlete with a waist circumference, at 34ins, is considered to have a healthy weight – if his height is 72 inches, his waist is less than half his height.
But the person with a sedentary life style with a waist of 40 inches is over half his height.