% Body Fat from a digital scale - how accurate?

tarquin_foxglove

I'm 1.8m tall weigh 70kg, the digital scales at home when set to 'Athlete' calculate my body fat at 7.1%. When I change the setting to 'normal' the body fat wobbles up to 16.4%.

Are they just working off pre-set ratios?

simple_salmon

They work by running a small electrical current through the lower limbs and measuring the impedance. From this they use pre-set equations based on your gender, height etc to estimate your overall body fat.

The 'athlete' setting is used because people who do 10+ hours of exercise tend to be more dehydrated and this should be taken into account.

Their accuracy is somewhere in the region of +/- 5% body fat; tbh I use them more as a measure of relative change over time than as an absolute figure.

There are far more accurate ways of measuring body fat but these are expensive and lab based; the method you are using is cheap and convenient but you pay the price in accuracy.

Hope that helps a little.

tarquin_foxglove

simple_salmon wrote:

Hope that helps a little.

It helps a lot, thanks very much.

ColinJ

I think that you should ignore the reading altogether!

'You pay the price in accuracy'...

Well if accuracy isn't important, I can give you an even quicker and more convenient way of checking your body fat. Use this table:

Monday: 14.2%
Tuesday: 13.7%
Wednesday: 15.8%
Thursday: 11.1%
Friday: 12.3%
Saturday: 14.5%
Sunday: (sorry, the batteries need changing!).

What use is a device whose reading changes significantly if you drink a glass of water, or if your feet are dry/sweaty?

I think you are much better off using a tape measure on your body at various strategic points if you want an indication of how much body fat you are carrying.

I know that I'm fat because I can get hold of the stuff and wobble it. I also know that I'm losing it at about 2/3 inch a week round my waist and that's enough information for me. If start to look skeletal like Michael Rasmussen, I'll know that I've gone too far.

If you are that bothered about the fat percentage, you'd get a more accurate measurement using fat callipers (providing that you learned how to use them properly or got someone else who knew what they were doing to take the measurements).

simple_salmon

ColinJ

The readings don't change drastically because of drinking water, wet feet etc but they can change by a couple of %. For tracking long term change they can be a useful tool; but I would exercise some caution about taking the readings overly seriously.

You don't get a 'more accurate' measure using fat callipers; the error rate is quite similar (or even a little higher) assuming that you used a trained person to measure. Using someone with less experience will obviously reduce accuracy as you point out. The regression equations used to calculate fat from the meaurements are even more general than those used by the fat scales and again should be interpreted with caution.

Waist circumference is a very useful measure of subcutaneous fat and associated health risks but again the measurement itself can be difficult to make with any high degree of accuracy: +/- 1 cm just by breathing for example.

tarquin_foxglove

ColinJ wrote:

If you are that bothered about the fat percentage

I'm not really, just weighed myself this morning for the first time since Christmas and as I got off the scales it flashed up 16.4% body fat, I thought 'am i f***!'. Switched the mode to athlete and got a much more satisfying 7.1% .

I just wondered if it actually measured anything or whether it was pre-programmed with averages, hence the large difference in the values but no change in me and I reckoned someone on here would be able to provide the answer.

andy_wrx

I just ignore what the value means, whether it's high or low, 'good' or 'bad' and see how it's changing.

I know I'm 6lb heavier than the same scales said I was in the middle of last summer and they then said my fat% was a bit lower than they say it is now.

I've started doing some upper-body weights and increased my riding and running, so presumably I'm getting fitter, but the weight hasn't changed
- however I can see the %fat has gone down 1%

prawny

TBF 7.1% is very low and 16% isn't bad at all I think the recommended range for chaps is 8-20% I'd be very jolly if my BF% was 16%.

I've got a didtal BF device thingummy and it's pretty consistant. I know i'm about 4-5lbs overwieght and my BF is about 18% which seems about right (i'm fairly ripped under my blubber y'know!!)

Eat My Dust

Hmm, I'd completely ignore them. My scales read about 28% fat (I've seen it as high as 32%!!!). I've got a 28" waist, and my abs are visible (just). I had my body fat measured years ago when I was in similar shape to now and the reading was 12%.

SBezza

My home scales show 26% body fat, though at our club night, we went on a specialist machine, and it showed less than 16%. I know which one I will believe.

The home one is good for watching trends, but it is not accurate at all.

dennisn

Don't know exactly what this means, but as an example, say you weigh 200 pounds
and the scale says 25% fat, this means you have 50 pounds of fat(so to speak). Say you lose 50 pounds and now weigh 150 yet the scale still says 25%, this means that you now have 37.5 pounds of fat on you even though the scale reads the same as it did when you weighed 200. I mention this only as a possibility and that the numbers are sort of extreme(only an example). So you've lost 12.5 pounds of fat yet still have the same percentage of fat in relation to your weight as you did at 200. While the fat percentage may not go down quickly enough for you the weight may be coming off anyway.
Whew, what a mouthful. I invite all comments on this as I'm somewhat of a skeptic on
fat monitors. I really think the old fashioned way of measuring skin pinches still works best. Or just look in a mirror. They don't lie.

Dennis Noward

SBezza

Dennis

You are correct, though if you lost 50 pounds, you would have probably put on muscle, and lost more body fat, so the percentage would normally go down as well. You are right though body fat percentages are slow moving, and electrical impedance does have errors in it.

LorneC

Well I started the year at 17st 5 lbs and 31.7% fat and currently at 15st 7lbs and 26.9% - as long as both figures are coming down.... I'm happy!!!

dennisn

SBezza wrote:

Dennis

You are correct, though if you lost 50 pounds, you would have probably put on muscle, and lost more body fat, so the percentage would normally go down as well. You are right though body fat percentages are slow moving, and electrical impedance does have errors in it.

You're right. Guess I should have made it say, lost 10 pounds and the scale stayed at
25% fat. That would have been a bit more reasonable. In fact, in thinking about it I seem to remember buying a cheapie hand held fat monitor because my wife wanted one and she had asked me how she could lose 15 pounds(which she had) and still have the same body fat percentage, more or less. The pinch and / or mirror method has always worked for me although of late it's getting scary doing either.

Dennis Noward

NJK

simple_salmon wrote:

ColinJ

The readings don't change drastically because of drinking water, wet feet etc but they can change by a couple of %. For tracking long term change they can be a useful tool; but I would exercise some caution about taking the readings overly seriously.

You don't get a 'more accurate' measure using fat callipers; the error rate is quite similar (or even a little higher) assuming that you used a trained person to measure. Using someone with less experience will obviously reduce accuracy as you point out. The regression equations used to calculate fat from the meaurements are even more general than those used by the fat scales and again should be interpreted with caution.

Waist circumference is a very useful measure of subcutaneous fat and associated health risks but again the measurement itself can be difficult to make with any high degree of accuracy: +/- 1 cm just by breathing for example.

If measured by someone who knows what they are doing then a body fat measure may be more accurate by fat calipers than a bodystat measurement, but as you have stated it does depend on the person taking the measurements.

simple_salmon

The skinfold (callipers) guideline I worked to when I was trained was that you should do 100 people before being considered competent.

It's also worth noting, as I mentioned above, that the regression equations used to calculate % body fat from the skinfold measures do not cover many people because they are specific to particular genders/races etc.

Having said that, I too prefer them when measuring people because I think you get a better 'feel' (excuse the pun) of what you are doing.

One final thing, if you are obese then skinfolds are VERY hard to do because you cannot pick up a true skinfold. Other types of BF measure are more appropriate.

Steve Kish

I use the formula:-

Height in metres squared = A

Weight in Kg = B

B divided by A = BMI percentage. I'm about 27 to 28% and as an old fat bastid, am not too unhappy with that. :roll:

Moaner

Gadgets are good, but home scales are not a good gadget.
You know when you're fat and when you're not.

dennisn

Moaner wrote:

Gadgets are good, but home scales are not a good gadget.
You know when you're fat and when you're not.

Ain't that the truth!!!!!


Dennis Noward

simple_salmon

Steve Kish wrote:

I use the formula:-

Height in metres squared = A

Weight in Kg = B

B divided by A = BMI percentage. I'm about 27 to 28% and as an old fat bastid, am not too unhappy with that. :roll:

BMI (Body Mass Index) is NOT a measure of percentage body fat. There is a correlation between the two but a BMI of 27 does not equate to a body fat of 27%.

As it happens a BMI of 25 - 30 (kg/m2) is considered 'overweight'. 30+ is 'obese'.

GavH

simple_salmon wrote:

As it happens a BMI of 25 - 30 (kg/m2) is considered 'overweight'. 30+ is 'obese'.

Just to add to this thought, a high BMI is quite normal in body builders, especially the really big ones. 'Good' body builders, ie the ones who do competitions, will also usually have a low Body fat % as that helps show the definition in their muscle groups. Hence BMI as a guide to how overweight you are is not really that cast-iron.

My scales have been telling me @20% BF for a while now. At 77 Kg I KNOW I have a fair bit worth losing. I recently returned from a outdoor trip where I'd lost 2 Kgs in the week. BF didn't change a noticebale amount, but the hydration level did. I know I wasn't drinking enough water during the week and true enough, it only took two days to get back to 77 Kgs, and nor was I stuffing my face either!

simple_salmon

GavH - you're quite correct; certain types of person will have high BMI without high body fat because of exceptional muscle levels.

However, for the majority of the general population this is not the case and BMI is a quick and easy way of keeping track of whether you could do with losing some fat.

My advice would be that if you're in the 25+ BMI zone (males) and you're not exceptionally muscular (body builder, rugby player etc) then this may be an indication that you need to lose a little weight.

Chaz.Harding

If you want some reasonably accurate way to measure bodyfat at home, look at the pro's and see how they guesstimate.

By pro's I mean pro bodybuilders. To them, fat % is everything. If you can just about see your abs, then it's about 10% ish. The more ripped you get, the lower BF% you have, obviously!!

Can just about see my abs.. Still a bit chubby after the Christmas hols :oops:

But with so many rides this year, will drop down later 8)

Chaz.Harding

If you want some reasonably accurate way to measure bodyfat at home, look at the pro's and see how they guesstimate.

By pro's I mean pro bodybuilders. To them, fat % is everything. If you can just about see your abs, then it's about 10% ish. The more ripped you get, the lower BF% you have, obviously!!

Can just about see my abs.. Still a bit chubby after the Christmas hols :oops:

But with so many rides this year, will drop down later 8)