Body Mass Index (BMI)

Body Mass Index

The body mass index (BMI) or Quetelet index is a value derived from the mass (weight) and height of an individual. The BMI is defined as the body mass divided by the square of the body height, and is universally expressed in units of kg/m², resulting from mass in kilograms and height in meters.

How do I calculate my BMI?

To work out your BMI:

1. Divide your weight in kilogram (kg) by your height in meter (m).
2. Then divide the answer by your height again to get your BMI.

What is the formula to check BMI?

The formula for BMI is:

In Metric Units

             BMI = Weight in kilogram (kg) / Height in meter square (m²)

In English Units

             BMI = Weight in Pounds / Height in Inches square (inch²) * 703

And round off the value up to one decimal place.

In general, a BMI over 25 is now the standard to indicate a person is overweight. While the healthy range is 18.5 to 24.9. BMI is applied to most adults 18-65 years.

Ranges:

BMI Value	Category
Less than 18.5	Underweight
18.5 to 24.5	Normal
25 to 29.5	Overweight
30 to 34.5	Obese Grade 1
35 to 39.5	Obesity Grade 2
Above and equal to 40	Obesity Grade 3

Fig: BMI Ranges

BMI Prime:

BMI Prime, a modification of the BMI system, is the ratio of actual BMI to upper limit optimal BMI (currently defined at 25 kg/m²), i.e., the actual BMI expressed as a proportion of upper limit optimal.

The ratio of actual body weight to body weight for upper limit optimal BMI (25 kg/m²) is equal to BMI Prime. BMI Prime is a dimensionless number independent of units. Individuals with BMI Prime less than 0.74 are underweight; those with between 0.74 and 1.00 have optimal weight; and those at 1.00 or greater are overweight. BMI Prime is useful clinically because it shows by what ratio (e.g. 1.36) or percentage (e.g. 136%, or 36% above) a person deviates from the maximum optimal BMI.

For instance, a person with BMI 34 kg/m² has a BMI Prime of 34/25 = 1.36, and is 36% over their upper mass limit. In South East Asian and South Chinese populations (see § international variations), BMI Prime should be calculated using an upper limit BMI of 23 in the denominator instead of 25. BMI Prime allows easy comparison between populations whose upper-limit optimal BMI values differ.

Why the BMI is not accurate?

BMI, which is based on the weight and height of a person, is an inaccurate measure of a body fat content and does not take into account muscle mass, bone density, overall body composition, and racial and sex difference, say researcher from the Perelman School of Medicine, University of Pennsylvania.

Fig: BMI In both Metric and English

Modified body mass index:

Within some medical contexts, such as familial amyloid polyneuropathy, serum albumin is factored in to produce a modified body mass index (mBMI). The mBMI can be obtained by multiplying the BMI by serum albumin, in grams per litre.

Fig: USA 2011 - 2014

Is BMI a good measure of health?

But in recent years, more researchers argue that it’s not the most accurate way to measure body weight. For years, scientists have said that BMI can’t distinguish between fat and muscle, which tends to be heavier and can tip more toned individuals into overweight status, even if their fat levels are low.

Macro Nutrient Distribution:

Nutrient	Distribution
Carbohydrates	40% to 60%
Proteins	15% to 20%
Fats	25% to 30%

Fig: Table of Nutrients Distribution

Nutrient	Energy per Gram (kcal/g)
1 g of Carbohydrates	4 kcal/g
1 g of Proteins	4 kcal/g
1 g of Fats	9 kcal/g

Fig: Table of Nutrient Energy per Gram (kcal/g)