A body mass index (BMI) measurement is a great thing if a quick and easy verdict is what you're after. For immediate judgement on whether you're underweight, healthy, overweight or obese all you have to do is:
Enter your height in metres and your weight in kilograms.
Simple, straightforward and unequivocal. Then why do so many of us feel the need to appeal the decision? Why do we seek a second opinion?
It comes down to the fact that, while impartial and generally useful, a BMI measurement can be a fairly blunt instrument. Dietitians and doctors acknowledge it has limitations.
All Blacks captain Richie McCaw clocks a BMI of 30, and therefore is classed as obese. So there must be more to the story.
What the BMI measurement is good for is indicating whether men and women with average 'frames' or 'builds' fall into one of four categories: underweight, healthy, overweight or obese.
When an athlete has much more muscle than the average person, this is not taken into account within the BMI calculation. Muscle is denser than fat and so it adds greatly to your body mass, helping make you heavier for your height without 'looking fat'.
Similarly, Pacific Island people tend to have a relatively higher proportion of muscle mass than people with European origins, so while they might tip the BMI calculator into overweight or obese, if the person is athletic, he or she might not have that much body fat. Many BMI calculators now allow for this and have moved the cut-off points.
The BMI measurement is not appropriate for athletes or bodybuilders, pregnant or breastfeeding women, growing children or the elderly who may have lost muscle mass.
Work out how to achieve your ideal weight.
The tale of the tape
More and more, doctors are saying that your waistline measurement is at least as, if not more, important to your long term health than your BMI measurement. Current recommendations are that a man’s waistline circumference should stay below about 100cm and a woman’s below about 88cm. At least one major study has shown that waist size correlates with the likelihood of getting type 2 diabetes later in life.
Apples and pears
The other way doctors and researchers look at this is by taking into account your waist-to-hip ratio: if you are overweight, are you an apple or a pear shape?
Measure your waist circumference at its narrowest point and your hips at their widest and divide the waist measurement by the hip measurement. For men, a ratio below 1.0 is considered healthy while for women a healthy ratio is below 0.8, according to the National Institute of Diabetes and Digestive and Kidney Diseases in the US.
The higher the waist-to-hip ratio, the higher the health risk. Some researchers believe this ratio is a better long term predictor of heart disease and diabetes than the BMI measurement.
The reason abdominal (belly) fat is thought to be more harmful to your health is that it could be more active hormonally and metabolically than fat stored on the hips, buttocks and thighs.
Article provided by UBM Medica (NZ) Ltd. For more health information and advice visit everybody.co.nz and liveto100.co.nz.
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