Body Mass Index is a way of assessing body fat for adults based on your height and weight.
BMI = weight (kg) / (height in metres) squared.
For example, if I weigh 65kg and am 1.78m tall, my BMI is 65/(1.78*1.78) = 20.5
The BMI categories (according to the US CDC) are:
| Normal Weight | 18.5 – 24.9 |
| Overweight | 25 – 29.9 |
| Obese | 30 or more |
BMI Limitations
It will overestimate fatness in people who are muscular or athletic (because muscle weighs more than body fat). And underestimates fatness in older people, and others who have lost muscle mass.
BMI was apparently developed by a US life insurance company during the 1940s to work out if clients were high or low risk.
BMI for children does not use this formula, as a child’s body fat changes dramatically as they grow. Detailed charts are used to measure body fat, dependent on child’s gender and age.
Other ways of measuring body fat
Pinch Test
Pinch the skin on your back just below your shoulder blades. Hopefully you can’t pinch more than an inch (2.5cm).
Waist Measurement
Over 35 inches (90 cm) around the waist for women is a risk factor for diabetes, heart disease and other ailments.
BIA – Bio-Impedance Analysis
Often available at gyms, these estimate body fat by measuring resistance to an electric current sent through the body.
A measured body fat level of less than 32 per cent is considered good health for women.
Unfortunately they are sensitive to body fluids, so are affected by your current hydration levels, and also do not cover the location of fat on your body.
And..
Your clothes: are they tighter than they used to be?
The mirror: be honest. Do you look fat?
Body fat is not the only way to measure fitness. Size, stamina, strength and suppleness are all areas to focus on.
Be careful. The Duchess of Windsor once said, ‘You can never be too thin or too rich”. Actually you can. Any extreme can be dangerous. Extreme weight loss can cause damage to vital organs such as the heart and brain, calcium loss to bones, dry skin, thinning hair, mood swings, temperature drops and more.