Assessments: Body Composition part 1 – Body Weight

I’ve split the Body Composition post into 2 parts.  In this part I’ll brief you on 3 simple ways to assess your body composition (Bathroom Scales, BMI and Waist/Hip Ratio). In part 2, I’ll go over some less common and more specialised ways to assess just how much body fat you have. First of all…What is body composition?

It’s all the different things that your body is made up of, and their relative proportions to each other.  In a practical sense, it means how much fat you have compared to your muscles/bone/blood/internal organs etc. A quick statistic for everyone out there: In England in 2007, 61% of adults were classed as overweight, obese or morbidly obese!  With only a little over a third classed as having “normal” weight.  (Get these stats from the NHS at:

Many many of us are thin, normal or fat

How many of us are underweight, normal or overweight

So how do you assess if you’re under/overweight or normal? There are a few different ways, each having its own advantages and disadvantages.  I’m going to very briefly tell you the main points now.

The Bathroom Scales

What are they:  You all know these.  You stand on them and they tell you how much weight is pressing down on them.  Simple.  This is by far the most popular way for people to decide if they are overweight or not.

Bathroom Scales


  • Cheap and simple.  they cost only a few quid and anyone can do it anytime.


  • They don’t give you any detail at all.  They give you the total weight of everything that is pressing down on them, including but not restricted to:
    • Your bones
    • Your body fat
    • Your blood
    • Your skin
    • Your internal organs
    • Your muscles
    • Your clothes/shoes
    • The highly fluctuating water content of your body (I read about an Ironman athlete who lost 8kg in one day of competition!  This was not a loss in fat, but a loss of water through sweat).
    • The contents of your stomach (eg the food and fluids you have eaten and drunk recently)
    • The contents of your bowels (eg the crap and piss you have not passed yet)
  • It is not comparable to other people.  eg, Sue is 4 foot tall and weighs 12 stone and Dave is 6 foot 6 and weighs 13 stone…does that mean Dave is fatter than Sue??  I don’t think so.

Summary:  Bathroom scales are good at telling if you are gaining/losing weight, but totally useless at telling if you are gaining/losing fat. Ask yourself if you want to lose weight or lose fat. If you want to lose fat, then consume slightly fewer calories than you burn day to day (click here for more details). If all you want is the scales to say you are lighter, you can try some of the following (I do NOT recommend any of these!!!):

  • Chop a leg off (a leg weighs a lot, without it you will weigh less…but you will probably die if you do this!)
  • Don’t drink anything for a few days (1 litre of water weighs 1kg.  If you don’t drink the recommended 2-2.5 litres of water a day, you will weigh less, but you will probably die if you do this!)
  • Sit in a sauna for a few hours (you will sweat out the water and weigh less…for a few minutes, until you have a drink and then you will be exactly the same weight as you were before)
  • Wear one of those silly silver foil suits when exercising.  You will sweat lots of water and weigh less…for a few minutes, until you have a drink and then you will be exactly the same weight as you were before)

I have a friend whose family is telling her she should drop down to 8 stone…why?  What is so special about 8 stone?  You can be 8 stone and be on deaths door, or 8 stone and an Olympic athlete.  It is meaningless! Avoid the Bathroom Scales method because it has nothing to do with your health and fitness.

Body Mass Index (BMI)

Body mass index graph

BMI Chart

What is it:  This is the “standard” way of telling if your body is a healthy weight or not and is the method used in the NHS report above.  It is: your weight (kg) divided by your height (m) squared.  For example, Billy-Bob is 70kg and is 1.8 metres tall.  His BMI will be 70/(1.8×1.8) = 21.6.

Your body composition is judged by the following:

  • Underweight – < 18.5
  • Normal – 18.5-24.9
  • Overweight – 25.0-29.9
  • Obese – 30.0-39.9
  • Morbidly Obese – >40.0

So Billy-Bob will be classed as “normal”.


  • Better than just the scales because it does take your height into account.
  • It has an “underweight” category, helping people realise that “less” is not always “better” (essential to help prevent eating disorders).
  • Very quick and simple to do.  All you need is a set of scales, a tape measure and calculator.
  • Easy and cheap to measure a great number of people.  This makes statistical analysis much easier and more accurate.
  • Very good and reliable on a “population” level.
  • Good association between an “average” persons BMI and their risks of various medical conditions.


  • Does not actually tell you anything about your body composition.
  • It has limitations for some groups of people that are not “average”.  eg many athletes and those with a history of regular, heavy weight training can have unusually high BMI’s due to the extra muscle mass.  Some elderly people can have unusually low BMI’s due to the natural decline of muscle mass with age.

Summary:  The BMI is a quick and easy way to assess the weight of the “average” person, works best on large populations, but it still does not tell us anything about what you are made of.  I find it useful for people who have never been active.  It is very quick and easy to do, gives them a nice simple answer at the end and often it helps people make the final step to improving their diet and activity levels. But if your BMI score is in the unhealthy range, please don’t do the usual things and say “it’s because muscle weighs more than fat”…because unless you really do train like a professional rugby player…I’m afraid it’s probably because your overweight. 🙁 Personally, I don’t bother much with the BMI scale for myself or any of the people I train.  When new people start training for the first time, there are so many different things happening to their body (not just fat loss) that their BMI score seems to go all over the place!

Waist/Hip Ratio

What is it:  This is a way to measure abdominal obesity, or how much fat you have round your belly.  It compares your waist and hips to give an idea of the distribution of body fat (to see if you are “apple” or “pear” shaped).  You get the score by dividing the circumference of your waist by your hips.  This is what the NHS says about carrying too much fat around your waist:

“Extra fat around your middle increases the risk for a number of serious health problems including diabetes, high blood pressure, high cholesterol, and an inadequate blood flow to part of the heart muscle, which can cause a heart attack.”

When you get your score, check where you fall in the following table:

< 0.85
0.85 – 0.90
0.90 – 0.95
> 0.95
< 0.75
0.75 – 0.80
0.80 – 0.85
> 0.85

This is usually used to work out potential health risks, as opposed to working out how much fat you are carrying.

Waist/Hip Ratio


  • Very cheap and  simple to do.  All you need is a tape measure and calculator.
  • If you are overweight and have started a good exercise programme, you may see improvement here before the Bathroom Scales or BMI.
  • Suitable to do on large groups/populations of people.


  • It does not estimate how much body fat you have.
  • You need to be careful to measure in consistent places or you will get different results without getting a different body.
  • Not much use for athletes and people who are fit and healthy, as it will just tell them what they already know – that they don’t have much fat round their belly.

Summary:  There is a good link between the waist/hip ratio and many health risks.  I would suggest to not bother using it for estimating how much body fat you have.  It was never meant to do that anyway.  It is best suited for sedentary people and those who currently are, or are borderline overweight.  As they get healthier they will see definite improvements in this score, which can be very motivating.

That’s the end of the first part!  Hope I have explained things properly…if not, just let me know and i’ll improve on it.

In the next bit, i’ll go over some more ways to assess your body composition…I’ll get it posted up within the week.

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