weight loss

Autumn and Spring, the transitional seasons, are a great time to take stock of your health and fitness. If you have been working out all summer or winter, it can be a good time to see how much you have improved. Just watching the scales isn't always the best way to go as there are too many other factors. So how do you find out what is healthy and how much you should lose?

BMI stands for your Body Mass Index, and is based on your weight to height ratio. It is one of the most common measures used because it is very easy, though does have some problems.

The BMI formula only requires your height and weight. The basic equation is your weight divided by the square of your height, done in kilograms and meters. BMI = Mass (kg) / (Height (m)2).

Let me show you a basic example. My current weight is 76kgs. And my height is 171cm. Therefore, BMI = 76/1.712 = 25.99. If you can't do the maths yourself, you can also just plug in the numbers to an online calculator such as the one at http://www0.health.nsw.gov.au/publichealth/healthpromotion/obesity/bmi.asp

But what does that mean exactly? Well, that's where the BMI chart comes in. The normal/health weight range is a BMI between 18.5 - 25. Anything below that is considered to be 'underweight', increasing in risk every 1 - 2 points below that, with less than 15 being very severely underweight. Everything over 25 is considered to be overweight, increasing in increments of 5 with over 40 being very severely obese.

So, according to the chart, I'm just bordering on overweight, so probably should get it down just a bit more, and can lose quite a bit and still be healthy. In fact, according to BMI I can actually get down to 54kgs and still be 'healthy weight'. And this is where the problem comes in. having once gotten down to 61kgs I can honestly tell you that 54kgs would not be a healthy weight for me. So is the BMI chart wrong?

The problem with the BMI formula, which has been raised by many people, is that the formula does not hold up very well if you are very tall and/or have quite a bit of muscle. As muscle is heavier than fat, and volume is cubed not squared, increases in height and muscle skew the results. So you still need to be sensible.

There are too many other factors such as muscle development and even how much you have had to drink will change the result. Anything that is based on weight is not going to accurately reflect your fat component. So, is there something better?

A more reliable formula, but harder to measure accurately, is your BFP: Body Fat Percentage. It focuses particularly on how much of your body weight is composed of fat. Keeping in mind that we need some essential fat to survive, and having a little bit more is not always bad, if you know your body fat percentage, you know how much you can lose safely.

Generally body fat percentages are as follows:

Description Women Men

Essential fat 10-13% 2-5%

Athletes 14-20% 6-13%

Fitness 21-24% 14-17%

Average 25-31% 18-24%

Obese 32%+ 25%+

The next thing you need to know is your body fat percentage. So how do you measure that? There are some high-tech ways to measure this, but it is unlikely you will be able to get your hands on these (dual energy X-ray absorptiometry anyone?). Better yet, get a personal trainer to measure you at a gym using one of the skinfold methods, though these are not perfect.

There are scales out there that measure your body fat for you, but these are actually very reliable. However, if you stick to the same set of scales, it should at least tell you if you are going up or down.

The best way to do it yourself is to buy some body fat calipers and do your own skinfold test. Calipers are not that pricy. The online calculator at http://www.linear-software.com/online.html can help you on the results without much difficulty.

So there you have it. My recommendation, work out your BMI just to see (and because it is easy) then see if you can book in to get a personal trainer to give you a proper skinfold test every 3- 6 months to see how you are going. If you are interested, buy your own calipers and give yourself the skin fold test. Whichever way you do it, I do recommend getting an externally validated estimate of your fat levels, because you may be surprised. Don't try to excuse it away, do something about it!