Re: So You Think You Know What Your BF% is Do You?

[Guest guest]

Rodney,

That was a nice experiment with all those BF measurements. Remember

the guy who as a stunt did not eat for 44 days? The papers below

about him show that although he lost 25% of his weight, the

percentage of fat only dropped by 2 percent from 20.1 to 18.1%.

For reference, the American Council on Exercise

assigns 6-13% body fat to the " athlete " category. A

range of 14-17% body fat corresponds to " fitness " , and

18-25% body fat is " acceptable " . The reason why this

is interesting, is that bodybuilders achieve

percentages in the range of 6% body fat by eating high

percentages of protein in their diet while restricting

calories (the cutting phase). Without the extra

dietary protein, fat and muscle are depleted at

approximately the same rate.

The data in these articles:

A 30-year-old male, weight 96 kg, height 1.84 m, at

the start of the experiment. The subject's final

weight after 44 days of 100%CR was 71.5 kg.

Percentage of fat before: 20.1 after: 18.1

Fat mass (kg) before: 19.2 After: 12.9

FFM (kg) before: 76.7 after: 58.6

BMR (kcal) before: 2047 After: 1723

Calculation of muscle loss relative to fat loss:

A BMR of 1723 for 44 days corresponds to 75,812 kcal.

This is the approximate number of calories required by

the subject while fasting for 44 days. (It may be

slightly more because the BMR changed during the

experiment) Since the fat lost was 6.3 kg(19.2-12.9),

at 3500 kcal per pound this corresponds to 6.3 x 2.2 x

3500 = 48,510 kcal that came from fat.

The remaining 27,302 kcal must have come from muscle

(and glycogen). Since protein and carbs have 4 kcal

per gram, the 27,302 kcal represent ~6.83 kg of

muscle. The remaining portion of the Fat-Free mass

loss 18.1 kg(76.7 - 58.6) was probably water (11.3

kg).

The result was that muscle (6.83 kg) and fat (6.3 kg)

were lost in approximately equal amounts.

If you want to decrease your percentage of body fat, you basically

have to do it the way that bodybuilders do it: increase the proportion

of protein in the diet while cutting down calories during weight loss.

Tony

===

1. Korbonits M, Blaine D, Elia M, -Tuck J.

Refeeding Blaine--studies after a 44-day fast.

N Engl J Med. 2005 Nov 24;353(21):2306-7. No abstract

available.

PMID: 16306536

2. JM, Blaine D, -Tuck J, Korbonits M,

Carey A, Elia M.

Macro- and micronutrient losses and nutritional status

resulting from 44

days of total fasting in a non-obese man.

Nutrition. 2006 Sep;22(9):889-97.

PMID: 16928474

3. Korbonits M, Blaine D, Elia M, -Tuck J.

Metabolic and hormonal changes during the refeeding

period of prolonged

fasting.

Eur J Endocrinol. 2007 Aug;157(2):157-66.

PMID: 17656593

>>>

=========

>

> Hi folks:

>

> A newly-opened local drug store is running sessions offering sort-of-

> useful free services to try to drum up business. These include a

> total cholesterol test, an ultrasound heel bone 'density' scan, and a

> BF% measurement, among others.

>

> The latter two are of interest to me, although I also had the

> cholesterol test done, which came out about where I had expected. I

> turned up for the BF% event recently, just agog waiting to see what

> the number would be.

>

> Soon after I arrived and was discussing general health issues with

> the RN who adminsters the test, I said that I wanted to drop my

> weight another five pounds to get to a BMI of 20·6. She

> replied: " You're slim, you certainly don't want to lose any more

> weight. " I explained that I had my reasons and she proceded with

> the test. It was done with a hand-held bioelectrical impedence

> gadget which has two handles. The patient holds one handle of the

> gadget in each hand, thumbs up, with arms extended out in front,

> horizontally, level with the shoulders.

>

> After entering some data in the gadget, which I believe included age,

> height and weight, the digital readout came up with the number. Ta

> daaaaaa: BF% = 20·4 !!! " You don't LOOK like a body fat of

> 20·4% " , she said.

>

> A few months ago the US Navy calculation had been saying my body fat

> was 14%. So after returning home from the drug store, I decided to

> do a Google search and calculate my BF% using all the methods

> available at the sites Google listed.

>

> The readings came in at anywhere between 9·7% and 23·7%. Here is a

> listing of the methods used and what they came out at most recently:

>

> US Navy: 17·5%

>

> -Pollock 3-circumference: 11.1%

>

> Biofitness.com: 23·7%

>

> Bio-impedence at drug store: 20·5%

>

> mac.com:

> Simple method: 9·7%

> Four skinfolds: 18·6%

>

> Csgnetwork.com - three circumferences: 20·5%

>

> Lowcarbdiets.about.com:

> A) 15·5%

> 14·1%

>

> Healthcentral.com: 15·3%

>

> Bmi-calculation.net: 18·14%

>

> NOTES

>

> As for the US Navy method, I notice huge variations in my neck

> measurement, measured exactly the same way, from week to week.

> Lately I have put on about four pounds of weight according to the

> scale, and my abdomen circumference has increased, yet my neck

> measurement has *dropped* from 15 " to 14 1/4 " !!! That change alone

> makes about 1.5% difference to my US Navy BF% result.

>

> A couple of the sites referenced by Google used skinfold

> measurements. Recently a report was posted (author Dr. Jimmy Bell)

> at to the effect that different people accumulate body

> fat in different places. Some people, according to this report, have

> much more visceral fat than others. I have since had that

> information confirmed by a radiologist I know, who says he sees this

> variation in full body CT scans. So it seems that this large

> variation in visceral fat among different individuals renders

> skinfold methods unreliable, since they are presumably unable to take

> account of the extent of visceral fat?

>

> How does a bioelectric impedence device measure visceral fat when it

> is held in both hands, with the electric current presumably running

> up one arm, across the body just below the neck, and down the other

> arm? Or fat any place, for that matter, except where the current

> flows?

>

> It seems to me all these methods rely on an assumption that fat in

> one specific location - the one measured - accurately reflects the

> amount of fat buildup everywhere. If Dr. Jimmy Bell is right, that

> assumption is wrong! In their introductory write-ups, most of the

> above sources claim their method is " highly accurate " . I suspect

> that none of them are reliable. For that matter is immersion

> reliable?

>

> Clearly this matters for people on CRON. If my body fat is really

> less than 10% then I have already exceeded my target and am beginning

> to approach the 'DANGER - do not go below' level. But if it is over

> 20% then I would have to lose another ~thirty pounds to get down to

> my tentative target of 10%.

>

> So how confident are *you* that you know what your BF% is? I am very

> confident that I do not know what mine is.

>

> Sigh.

>

> Rodney.

>