Estimating bodyfat: RFM

[JohnHelton]

Formulas can give precise results, assuming the inputs are measured precisely. That, of course, doesn't make them accurate. They don't need to be (very) accurate. They just need to be precise in order to demostrate changes over time.

As @TimK says, if you plug weight and waist measurements into a formula that spits out a fictitious "body fat" measurement, you really don't know anything new. Especially if that fictitious number is very different than the actual BF%.

However, if someone gave me a random weight and waist measurement (say 220 lbs. and 38 in. waist), I really couldn't tell you how fat they are without seeing a picture (no thank you). In other words, I think I know what 10%, 15%, and 25% look like, but I don't know what they translate to in terms of various weight/waist combinations. The ability to reduce two numbers to one for comparison purposes has that benefit.

[michael]

I guess if you want to boil everything down to a single number, it's fine.

So fahves for everything?

[TimK]

I guess if you want to boil everything down to a single number, it's fine.

So fahves for everything?

Just add 5 inches (to your waistline).

[michael]

I guess if you want to boil everything down to a single number, it's five.

FTFY.

Goddammit. I missed it the first time.

[michael]

I never trusted the navy method.

I have always seen neck size increase proportionally to fat gain. Notice that the neck on a x-large dress shirt is 18" and a medium is 15".

I know that normal weight training does not increase neck size much (to increase neck size you need to do direct neck work).

So I don't understand, or trust, that the formula gives a lower bodyfat percentage for a larger neck.

When I'm quite lean the Navy and YMCA formulas are super close, but as I get fatter Navy gives a lower number.

[JohnHelton]

I never trusted the navy method.

I have always seen neck size increase proportionally to fat gain. Notice that the neck on a x-large dress shirt is 18" and a medium is 15".

I know that normal weight training does not increase neck size much (to increase neck size you need to do direct neck work).

So I don't understand, or trust, that the formula gives a lower bodyfat percentage for a larger neck.

When I'm quite lean the Navy and YMCA formulas are super close, but as I get fatter Navy gives a lower number.

That makes sense. I'm sold on the YMCA method.

[quark]

There exist various anthropometric methods for estimating body fat. The term anthropometric refers to measurements made of various parameters of the human body, such as circumferences of various body parts or thicknesses of skinfolds. Most of these methods are based on a statistical model. Some measurements are selected, and are applied to a population sample. For each individual in the sample, the method's measurements are recorded, and that individual's body density is also recorded, being determined by, for instance, under-water weighing, in combination with a multi-compartment body density model. From this data, a formula relating the body measurements to density is developed.

Because most anthropometric formulas such as the Durnin-Womersley skinfold method,[13] the Jackson-Pollock skinfold method, and the US Navy circumference method, actually estimate body density, not body fat percentage, the body fat percentage is obtained by applying a second formula, such as the Siri or Brozek described in the above section on density. Consequently, the body fat percentage calculated from skin folds or other anthropometric methods carries the cumulative error from the application of two separate statistical models.

These methods are therefore inferior to a direct measurement of body density and the application of just one formula to estimate body fat percentage. One way to regard these methods is that they trade accuracy for convenience, since it is much more convenient to take a few body measurements than to submerge individuals in water.

The chief problem with all statistically derived formulas is that in order to be widely applicable, they must be based on a broad sample of individuals. Yet, that breadth makes them inherently inaccurate. The ideal statistical estimation method for an individual is based on a sample of similar individuals. For instance, a skinfold based body density formula developed from a sample of male collegiate rowers is likely to be much more accurate for estimating the body density of a male collegiate rower than a method developed using a sample of the general population, because the sample is narrowed down by age, sex, physical fitness level, type of sport, and lifestyle factors. On the other hand, such a formula is unsuitable for general use.

https://en.wikipedia.org/wiki/Body_fat_percentage

[anelson]

I think RFM is supposed to be a BMI analog, as opposed to a bodyfat percentage measurement. The way the formula is set up, most people will be in the twenties, it appears.

[cwd]

Waist size is pretty easy to measure. RFM should be superior to BMI while still being easy to use.

I can't find a use for a firm bodyfat % number. For training and diet, e1RMs, waist, and weight are enough.

The exception is for knowing where to start/stop cuts and bulks. The bodybuilder consensus is to stay inside 10% to 15% bodyfat. But I can't figure out where these numbers come from, scientifically. I suspect they are purely aesthetic.

Maybe one could use 15-20% instead, if one doesn't care about abz? Is there any evidence that 15% BF is healthier than 20% for men?

[quark]

It's harder to research BF, because BF is harder to measure than waist, weight, height or the like. DEXA or hydrostatic appear to be the only accurate measures (see the wikipedia article I linked above) and they're obviously not an easy thing to do for lots of people.

@JordanFeigenbaum often cites research about waist size and BMI (although he tends to ignore BMI) as being important, especially waist over 40" (for men). He appears to regard 40" as a bright line test.

Sometimes researchers into the general topic show up on reddit or other public forums, usually to discuss a paper that correlates BMI with health. Whenever I see that, I ask if the issue is BMI or BF. The answer is invariably BF, but that they use BMI because it's easier to measure, is in widespread use and is a reasonable proxy for populations (as opposed to for every individual).

[cwd]

@JordanFeigenbaum often cites research about waist size and BMI (although he tends to ignore BMI) as being important, especially waist over 40" (for men). He appears to regard 40" as a bright line test.

Right, the 40" waist for men is clearly on the side of too fat for best health outcomes.

What waist measurement would be ideal for health though?

[michael]

@JordanFeigenbaum often cites research about waist size and BMI (although he tends to ignore BMI) as being important, especially waist over 40" (for men). He appears to regard 40" as a bright line test.

Right, the 40" waist for men is clearly on the side of too fat for best health outcomes.

What waist measurement would be ideal for health though?

I think waist should be <= 50% of height.

http://prowellness.vmhost.psu.edu/famil ... _risk/whtr

[quark]

@JordanFeigenbaum often cites research about waist size and BMI (although he tends to ignore BMI) as being important, especially waist over 40" (for men). He appears to regard 40" as a bright line test.

Right, the 40" waist for men is clearly on the side of too fat for best health outcomes.

What waist measurement would be ideal for health though?

I think waist should be <= 50% of height.

http://prowellness.vmhost.psu.edu/famil ... _risk/whtr

waist to height for a male:

Ratio 43% to 52%: healthy weight

I like that answer, given that I'm currently about 51.4%.

There appears to be a major difference between visceral and subcutaneous fat, which difference is elided by just focusing on waist size or overall bodyfat. "Excess visceral fat is also linked to type 2 diabetes,[11] insulin resistance,[12] inflammatory diseases,[13] and other obesity-related diseases.... subcutaneous fat is not related to many of the classic obesity-related pathologies" https://en.wikipedia.org/wiki/Adipose_tissue

[cwd]

So at 5'10" my healthy waist sizes would be 30.1" to 36.5". The Navy calculator would put me at 10-22% bodyfat for those waist sizes.

How does one know how much visceral fat he has?

[michael]

So at 5'10" my healthy waist sizes would be 30.1" to 36.5". The Navy calculator would put me at 10-22% bodyfat for those waist sizes.

How does one know how much visceral fat he has?

Waist size is basically a proxy for visceral fat.

[mbasic]

So at 5'10" my healthy waist sizes would be 30.1" to 36.5". The Navy calculator would put me at 10-22% bodyfat for those waist sizes.

How does one know how much visceral fat he has?

Waist size is basically a proxy for visceral fat.

[cwd]

So at 5'10" my healthy waist sizes would be 30.1" to 36.5". The Navy calculator would put me at 10-22% bodyfat for those waist sizes.

How does one know how much visceral fat he has?

Waist size is basically a proxy for visceral fat.

Yes, but...

On my current cut, I feel like my waist has shrunk more (37 to 34.5" so far) than can be accounted for by the loss of subcutaneous fat. I was carrying some visceral fat too.

And I didn't think I was carrying visceral fat, because I exercise a lot. I thought I had a "healthy dad-bod" with mostly subcutaneous fat.

[michael]

So at 5'10" my healthy waist sizes would be 30.1" to 36.5". The Navy calculator would put me at 10-22% bodyfat for those waist sizes.

How does one know how much visceral fat he has?

Waist size is basically a proxy for visceral fat.

Yes, but...

On my current cut, I feel like my waist has shrunk more (37 to 34.5" so far) than can be accounted for by the loss of subcutaneous fat. I was carrying some visceral fat too.

And I didn't think I was carrying visceral fat, because I exercise a lot. I thought I had a "healthy dad-bod" with mostly subcutaneous fat.

Increased central (abdominal) adiposity has a special importance be-cause of increased risk of cardio-metabolic disorders. Waist circumference (WC) is the best simple index of fat distribution, since it is least affected by gender, race, and overall adiposity.

So the waist measure is the best indication of visceral fat because it has the smallest proportion of subcutaneous fat.

If you did have a ton of subcutaneous abdomen fat, you'd have loose flaps of skin once you lost it all.

[cwd]

Waist size is basically a proxy for visceral fat.

Yes, but...

On my current cut, I feel like my waist has shrunk more (37 to 34.5" so far) than can be accounted for by the loss of subcutaneous fat. I was carrying some visceral fat too.

And I didn't think I was carrying visceral fat, because I exercise a lot. I thought I had a "healthy dad-bod" with mostly subcutaneous fat.

Increased central (abdominal) adiposity has a special importance be-cause of increased risk of cardio-metabolic disorders. Waist circumference (WC) is the best simple index of fat distribution, since it is least affected by gender, race, and overall adiposity.

So the waist measure is the best indication of visceral fat because it has the smallest proportion of subcutaneous fat.

If you did have a ton of subcutaneous abdomen fat, you'd have loose flaps of skin once you lost it all.

I get that waist size is the best indication of visceral fat short of an expensive 3d scan that can look through the abdomenal wall. Fat elsewhere on the body by definition isn't around your viscera!

I'm disturbed that I think I was carrying a fair amount of visceral fat (and maybe still am carrying some) and didn't know it. How many of us on this forum are rocking big bellies and big muscles, and thinking they are healthy-fat when they aren't?

I think that whichever variety of fat my waist size came from, losing it would free up about the same amount of loose belly skin

[michael]

I think that whichever variety of fat my waist size came from, losing it would free up about the same amount of loose belly skin

Nope.

A "power-belly" is visceral fat. A "beer-gut" is visceral fat.

You have normal waist now, so it's okay.