Thursday, January 21, 2021

Body Mass Index: How it Works


Body Mass Index (BMI) is a measurement of a person’s body fat in relation to their height and weight. BMI is used to more accurately assess a person’s risk factors. It’s not enough to simply step on the scale anymore to determine whether you are healthy or not. Since muscle weighs more than fat and metabolizes calories faster than fat, its important to differentiate healthy weight in the form of muscle and unhealthy weight in the form of excessive fat.

Calculating BMI

BMI is calculated by dividing the weight in pounds by height in inches squared and multiplying by a conversion number of 703. The formula looks like this:

[height (in) / (weight (lbs)) 2]

x 703      or

[weight (kg) / [height (m)]


Once you arrive at your BMI calculation, you can determine the corresponding weight status.

  • Underweight = <18.5
  • Normal weight = 18.5-24.9
  • Overweight = 25-29.9
  • Obese = 30 or greater

BMI Reliability

BMI isn’t the most reliable source of body fat measurement. Other factors like sex, age, and race play a part in the amount of body fat a person has. For example, older people tend to have more fat per pound than a younger person. Women usually carry more fat than men. And, an athlete may have a high BMI, when instead of fat the athlete has extra muscle creating more weight.

Alternatives for Fat Measurement

There are other methods for measuring a person’s body fat. The one most commonly used by professionals is underwater weighing. This takes into account the difference in mass of bones and muscle and fat. A person is weighed outside the water and then submerged in the water. They calculate the difference and arrive at the body fat composition.

Another less expensive method for measuring body fat is calipers. Calipers are small, lightweight, and cheap. You can take them with you wherever you go and they measure folds of skin in various places on the body. Their effectiveness is really based on how trained the person is doing the measuring. You need to learn how to use calipers to determine body fat, but once you do it’s an easy way to stay on top of excessive fat.

Bioelectrical impedance is a fancy name for safe electrical currents being sent through your body to determine how much fat it encounters along the way. As the current travels through the muscle, fat, and bone tissue, the electrical signals are calculated. There are scales available that measure body fat this way. You stand on metal sections of the scale and an electrical signal is sent through your body. You don’t feel a thing, it takes only a few seconds, and you can track your progress with weight and body fat with your scale. Tanita is one of the best inexpensive body fat digital scales.

Your BMI is a guideline for you to assess where you are with your weight and body fat percentage. Its not meant as a definitive number that gives you precise measurements.

Medically trained in the UK. Writes on the subjects of injuries, healthcare and medicine. Contact me

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