What is BMI

BMI, or Body Mass Index is a tool used to measure the fat composition in a person’s body based on their weight and height.

Calculating a person’s BMI is simple. The formula is a person’s weight in kg divided by their height in metres squared. The result shows if a person is underweight, healthy, overweight, or obese.

BMI for women

A healthy woman’s BMI ranges between 18.5-24.9

BMIWeight classification
Below 18.5Underweight
30.0 or higherObese

For pregnant women, there is a chart which uses their BMI before pregnancy to calculate recommended weight gain during pregnancy.

BMI before pregnancyRecommended pregnancy weight gain
Below 18.528 to 40 pounds
18.5-24.925 to 35 pounds
25.0-29.915 to 25 pounds
30.0 or higher11 to 20 pounds

Lambert Adolphe Jacques Quetelet, a Belgian mathematician, came up with the formula for BMI in the 1830s. The BMI scale was developed to help the government allocate resources by identifying the degree of obesity in its citizens.

BMI has been used a marker for a person’s weight classification measured by their body fat since the last 200 years. In recent years, there have been many reports suggesting that BMI is not an accurate marker of health, especially for women.

There are many reasons behind this:

  • If a woman is an athlete: Active people tend to have more muscle mass. As a result, BMI does not reflect body fat or muscle mass, so it’s useless for athletes. In addition, muscle with a higher density weighs more.  That, in turn, skews BMI results and athletes are likely to fall into the obese or overweight range

  • Postmenopausal Women: In general, as you grow older, your body fat tends to increase. When women go through menopause, their hormone levels drop. When hormone levels fall, muscle mass decreases and belly fat increases. You may have much more body fat at 70 than at 30, even if you weigh the same. There is even evidence that some postmenopausal women with a healthy BMI are overweight or obese.
  • Inaccurate for non-Caucasian women: Your ethnicity can affect your body fat distribution and muscle mass. According to one study, women of Mexican descent have more body fat than white or black women. The study found that Black women tend to have more muscle mass than white women or those of Mexican descent. BMI does not account for these differences. Different ethnicities, including white, black, south asian and middle eastern, have also been found to be at a higher risk of developing Type 2 diabetes at different BMI scores.

The best way to know if your body fat percentage is affecting your health is to know by going to a licensed expert in the field.