I always do as I am told. I comply with instructions to the letter except the instructions that come with IKEA flatpacks. Why do my shelves look like swedish meatballs. But I digresss....

I have just been computing my body fat % as instructed in chapter 4 of PP. Wrist measurement three times. Did that . I felt so stupid, it was the same each time! In what way could I have got it wrong I am not sure.

Waist measurement three times. Ok, Eades has a point here I have trouble with the exact definition of waist. Is it where the belt goes round or is it the smallest circumference between hips and stomach? It turned out that my belt seems to find the least line of resistance anyway. Measured three times again. Exactly the same. I have consistency honed to perfection. It occured to me that perhaps it should be measurements over seperate days. But I follow instructions to the letter and it did not say to do that.

Now subtract waist minus wrist. Only do this once because mathematics is an exact science and it should not vary too much each time you do it.

Now weigh yourself. I was just stepping on the scales for the third time when I noticed that you only had to measure weight once. I humbly beg to differ with Dr. Eades. My weight is a matter of opinion, its calculation is now a fine art form and would need more than three times let alone a solitary weigh in.

The task now is to read off a chart with pounds on one axis and "waist minus wrist" calc on the other. Did that. All the accuracy of the average of three calculations is now superflous because the increment of measuerement for size increases by only half inches and the weight by 5 pounds.

And low it came to pass that my percentage of body fat read 29.

I turned the page to find out what is the relationship between waist minus wrist and weight and......nothing, zip, nah nah.

And I really wanted to know. I had obeyed all the instructions and yet Dr. eades could have thought up the first number that came into his head for all I know. I felt cheated.

Now don't get me wrong I love PP and I recommend it to anyone, but Dr. Eades ( or anyone else)if you are reading this can you put me out of my misery I am just dying to know.

Oh and Dr. Eades please read this post three times before replying. Ve haf vays of making you talk!

you crack me up, rust.

I don't know the answer, but ran across BF computation formulae the other day by doing an internet search for "body fat formula"

What I found were formulae that had me anywhere from 19 - 34%, based on the same measurements. That's helpful, I thought. I'm either morbidly obese or starving to death! Luckily, had the BF tested at the gym, so I know it...but it was instructive to see how inaccurate the measuring systems are.

Razzle,

I suspect a conspiracy at work. It is posssible that aliens have infiltrated society and are secretly fattening us up for the pot. Just to keep us guessing they issue misleading information so that we do not notice our increasing fat %.

Well let me tell you Mr. Alien it had better stop! and right now, thank you very much. So there.


PS

The calculation for women is completley different. Its Hips Abdomen and Height. Don't ask me why, or what the relationship is. Dr. eades does not say (have you noticed his pointy ears)Suffice to say that I go for the sex change to-morrow because as a woman I am only 26%.

Now you wouldn't except the extra male bits would be that much fat would you?

I hope by each tme you mean from several tries at the same time/day, not each time you measure weekly or months

The tables in PP are a reproduction from "the complete book of physical fitness" which are often sited by other books to estimate body fat.

However, it is possible for people to lose weight, and yet maintain the same body fat ratio Which implies a loss of both muscles and fat, due to several factors, including lack of activity and/or undereating.

Wa'il

Yup, it was one measurement after another. I actually did it six times as I have two wrists and one might have been fatter than the other!

So I am off to look up the complete book of physical fitness now.

I may be some time. Please everyone carry on without me.

What did I do with my tape measure

Couldn't find the book but the journal of statistics came to my aid.

I wish I had not asked!

As a variety of popular health books in addition to Protein Power suggest that readers assess their health, at least in part, by estimating their percentage of body fat.
15 percent fat for men and 22 percent fat for women seem to be maximums for good health often quoted.
How exactly are they doing the estimating has been my quest.

These predictive equations in books and the odd website use skinfold measurements, body circumference measurements (e.g., abdominal circumference), and, some simply height and weight.

The secret equation for the determination of body fat is determined through .....multiple regression.

A group of subjects is gathered, and various body measurements and an accurate estimate of the percentage of body fat are recorded for each using water density more of that in a minute.

Then body fat estimates can be fitted to the other less wet measurements using multiple regression , giving, we have to believe, a useful predictive equation for people similar to the subjects.
The various measurements other than body fat recorded on the subjects are, ones that are easy to obtain and serve as proxies for body fat, which is not so easily obtained.

Body fat apparently can be fairly accurately recorded by an underwater weighing technique as the percentage of body fat for an individual can be estimated from body density.
As an approximation, it is assumed that the body consists of two components -- lean tissue and fat tissue.

It now gets a bit technical so go and make the tea and come back in a little while-

One method (brosek)says:

Let

D = body density,
W = body weight,
A = proportion of lean tissue,
B = proportion of fat tissue (so A + B = 1),
a = density of lean tissue, and
b = density of fat tissue,
we have

D = weight/volume
= W/[lean tissue volume + fat tissue volume]
= W/[A*W/a + B*W/b]
= 1/[(A/a) + (B/b)].
Solving for B we find

B = (1/D) * [ab/(a - b)] - [b/(a - b)].

Using the estimates a = 1.10 gm/cm^3 and b = 0.90 gm/cm^3 we come up with "Siri's equation" (Siri 1956):

Percentage of body fat (i.e., 100 * B) = 495/D - 450,
where D is in units of gm/cm^3.

This is considered accurate for "individuals in whom the body weight has been free from large, recent fluctuations."

Now wake up at the back there![/ B]

We all remember Archimedes and his bath..... well-- [B]the technique of underwater weighing "computes body volume as the difference between body weight measured in air and weight measured during water submersion . In other words, body volume is equal to the loss of weight in water with the appropriate temperature correction for the water's density" (Katch and McArdle 1977, p. 113).

Using this technique,

Body density = W/[(W - WW)/c.f. - LV],

where

W = weight in air (kg)
WW = weight in water (kg)
c.f. = water correction factor
(equal to 1 at 39.2 degrees F because one gram of
water occupies exactly one cm^3 at this temperature,
equal to .997 at 76-78 degrees F)
LV = residual lung volume (liters)
(Katch and McArdle 1977, p. 115).


So all we have to do is fit 300 people in my bathroom........

Determine
their Percent body fat using Brozek's equation

Then record
Density (gm/cm^3)
Age (yrs)
Weight (lbs)
Height (inches)
Adiposity index = Weight/Height^2 (kg/m^2)
Fat Free Weight= (1 - fraction of body fat) * Weight, using Brozek's formula (lbs)
Neck circumference (cm)
Chest circumference (cm)
Abdomen circumference (cm) "at the umbilicus and level with the iliac crest"
Hip circumference (cm)
Thigh circumference (cm)
Knee circumference (cm)
Ankle circumference (cm)
Extended biceps circumference (cm)
Forearm circumference (cm)
Wrist circumference (cm) "distal to the styloid processes"

Carry out a multiple regression analysis which I don't know how to do and then you can infer fat percentage of everybody else in the world without them getting wet by any combination of the other measures.

Now look are you still paying attention because there is a term paper in a few weeks.

Do you think that this could really be true?

You might want to check out my post on this subject in the General LC forum.

Even the water-based water density measurements - which are the accepted gold standard for %BF calculations - are only an estimate because of the very assumption you mention. You have to assume that the body is made up of just the two tissues and that you know the density of the two. That assumption imposes, as near as I can determine, about a 5% margin of error on BF measurements. This can be reduced by using frame structure and race-based corrections to compensate for the amount of bone and the different bone densities that are known to have a strong racial correlation.

The only other method, that I am aware of, that comes close is BIA when it is done according to very precise protocols. Even then it appears to be at about the 10% margin of error.

So as not to confuse people on the difference between a 10% error and a 10 percentage point error, if your measurement came out to be 20% fat, then a 10% margin of error would place your actual value between 18% and 22%.

I don't know why I didn't catch this thread when it started . . . but glad I'm here now!

I used to work for the federal government (no, not a spy) doing research, and I was the body fat measurer for a study, lo and behold.

We would actually use several methods to determine body fat, and then compare them all to each other. We used Bioelectrical Impedance Analysis (BIA), skinfolds and circumfurences (tape mesurements) used in those regression equations, water displacement (underwater weighing), and air displacemant (new thingy called the BodPod - looks like Mork from Ork's transportation).

As already mentioned, they all have a margin of error. Now on to the good stuff . . .

In the research study, none of the measurements taken by each method were ever the same. But we did find that OVER TIME, the increase or decrease in measurements did correlate nicely.

What's my point? If you pick one method, and follow your measurements over time, the loss you see actually does mean something: You LOST body fat!! Just stick with ONE method.

Isn't it more important to evaluate your weight/fat loss than the method of measuring it? Personally, I prefer the "clothes are getting bigger on me" method

Suz: You might be able to answer a question I have been trying to track down. I know that the clinical BIA measurement have a good correlation, but I can't find any information on the performance of the cheap commercially available BIA "instruments". It's my understanding from some time ago that they fair rather poorly in both their reproducibility and their ability to correlate to changes because of the huge variables that are not controlled or compensated for. Did your study involve any BIA measurements other than the accepted clinical methods?

Suz:

Your point is well made and fascinating that you have been so involved.

Where I, and I think Bill also, are having these nagging doubts is the degree of confidence in, or the margin of error of, the BF% calculations which are then used as either a benchmark to achieve or in the case of PP the specific protein requirement per day required.

If all we were measuring was progress over time then the scales do that quite nicely.

If there is a relatively cheap reliable method that does not need the combined research departments of our respective govts. I would be interested and......

...... would obey every instruction to the letter!

Unfortunately, my study was for clinical purposes only, so the instrument we used is by the manufacturer RJL Systems, which is most commonly used among researchers. A really good reference to the BIA method is at the link below.

http://www.rjlsystems.com/research/bia-principles.html

Because hydration status of the subject, room or skin temperature, age, gender, ethnic origin, level of physical fitness, and other individual characteristics may all contribute to differences in the observed measurements within BIA, its important to have a tool that is high in sensitivity and specificity. Those cheaper tools are so variable (I have seen them used in gyms), and of course the level of training of the person performing the test is also not consistent.

I don't know if I've actually answered your question . . . but I will say that I would trust a GOOD skinfold measurer over a cheap BIA test or a Tanita scale anyday. Just make sure they use 8 or more measurement spots to plug into the equations. # or 4 do not suffice, and of course lead to greater error.

Happy body fat measuring!!

Suz

Thanks for the info. I was reading RJL's site a week or so ago - it's about the best one I've seen yet. The information there and what you have provided plus some basic EE all agree that the cheap meters are basically worthless.

Hey, Rust, I love a theme party! Just let us know.

Talk about close friends!

Hello Mr. Rustpot,
I'm sorry, I cannot help u with your questions or the Swedish meatballs (well, I'd happily eat them for u if they were low carb & not from Ikea). I'm here to tell u that I've been reading your posts & I've enjoyed each and everyone of them Your posts are like, British humour at it's best!
I'm looking at the cover of my PP. To be honest, Dr. Michael Eades' ears look fine & normal to me. However, the man in the pale-blue shirt, the 3rd one from your left, on the upper row, u know, the one with glasses on, now, his ears do like suspiciously pointy to me.......
Thank u for the endless supply of humour & great laughs, sir. Please keep them posts coming.
your biggest fan,
Bebe