Determining desired weight using known BMI

I have been calculating clients BMI using Calipers and a 4 site method (Tricep, Bicep, Sub scap, and suprailiac)

The sum of these allows me to use a chart to estimate % of Body Fat as well as estimated lean body mass (muscle gain/loss)

The method given to determine 'desired body weight' is;

Present weight

100 - current bodyfat % = (x)
100 - desired bodyfat % = (y)

(x) / (y) = (z)

desired weight = current weight x (z)

for example

Current weight = 73.3kg
Current % = 33.5%

If my clients desired % of body fat was 20% (between 14 - 21% given as 'healthy')

then using the above calculation

100 - 33.5 = 66.5
100 - 20 = 80

66.5/80 = 0.8312

73.3 x 0.8312 = 60.9 <---------------desired weight  @ 20% body fat

This means that to have 20% bodyfat my client has to lose 12.4kg, which i believe is just silly.

Thinking about this more, I notice that this equation doesn't take into consideration an increase in lean mass due to muscle gain

which we all know is vital for sustainable weight loss.

I guess my question to you all is how do i answer the question my clients have when they ask what weight should they be?

Surely adding in an increase in muscle mass for my client in the above scenario would be closer to 63kg- 65kg?

Any suggestion as to what formula I should be using, if I am doing anything wrong or if i am missing something completely

Any help or comments appreciated

Sam Hall

www.wybo.co.nz

p.s hope this all makes sense to someone

Hi there Sam, thanks for your posting.

My short answer is that i'm not aware of any formula that you can use to tell a diverse range of people what they 'should' weigh.  

Longer answer and explanation is; Such a formula doesn't and couldn't exist - why?  Because people are all uniquely different - the 'ideal' weight for a rugby player will be different to that of a distance runner.  The ideal weight of a heavy set person for 'health' will be different for a lean person for 'health'.  In fact there are so many factors to consider that the concept of there actually being an 'ideal' weight for people and a way to calculate this is pretty flawed, in my opinion anyway.

When your clients ask you what weight they should be I'd be inclined to ask them what weight they'd like to be and why they consider that a good weight.  Society does tend to have a fixation (an unhealthy one in my view) on 'weight' and what is ideal.  Because of this societal fixation on weight I find that many clients come to us wanting to alter their weight or wanting to know what they should weigh as they sort of expect that altering their weight is something they should do because everyone else seems to consider it important.  

When it gets down to brass tacks however I find that most clients actually want something much more specific and personal than to reach an ideal weight - they might want to lose the fat rolls that extrude over their jeans, to feel better about their appearance, to feel more energetic, to get stronger and improve their appearance of 'tone'.  Whatever their individual reason I'd advise you to spend more time with them defining exactly what they want to achieve and why that is important to them, and how they'll work towards achieveing their goals.  

Hope that helps,

Regards

Daniel

Thanks for that Daniel. I was expecting an answer along those lines

I am more than happy setting goals to decrease BMI readings and lean

mass from my calipers, instead of a weight figure. Was interested in the manual that

came with the calipers giving such equations in the first place.

If the lean muscle mass is increasing/staying the same and BMI is decreasing what more can

you ask for in a weight loss programme

Thankyou again, hoping more people join and ask more questions 

Sam