How to determine body fat

[B3]

Last week my weight was 128.8 pounds and this week I am 127.8, so during the week how much body fat did I lose?

[wmchapman]

Depends on your height and gender @B3

It is used to find your lean weight which is subtracted from your actual weight, and then that difference is divided by your actual weight.

Guessing 30.1% body fat to start at 128.8 lbs , lean 90 lbs

I would guess 1lb loss would be body fat 29.6% or a half percent reduction.

[Dominique]

There are several methods for estimating changes in body fat: skinfold calipers (example), bioelectrical impedance analysis (typically, with scales like the Fitbit Aria or similar), Bod Bod, DEXA scans etc. Did you use any of these? If not, it’s simply impossible to infer anything from the 1 pound change in body weight you observed. And even if you did, one week is way too short to assess any meaningful change.

[B3]

No I don't use any of these things, how long will I know the difference if I lose body fat?

[Dominique]

Use a tape meter and take body measurements, for instance your waist circumference at the level of your belly button. If you’re losing fat, it should shrink. However, it may take several weeks before you start detecting meaningful changes.

[GershonSurge]

Unless you use a scale that measures body fat, you will have no way of knowing. The other methods are complicated and likely not worth the effort. However, rest assured that if you are losing weight, in the long term, you will lose body fat. BMI and a good look in a mirror is a good enough indicator for most people.

Short-term fluctuations are random and mean little.

Exercise combined with weight loss may help, but it's not guaranteed. For now, I suggest very gradually increasing the number of steps you get each day.

If you don't have a scale, I recommend getting one at Walgreen's. They have scales for about $30 that measure body fat. 

[wmchapman]

We've all been there, done that. Looser clothes, tighter belts and the ability to do isometric exercise are all the cues.  Look at the BF reading as a guide, not a goal. Interesting enough when you've been at it a lonnnng time the BF % proves itself as a guide because the more fit you get the higher your actual lean weight rises with muscle development. You'll drive yourself crazy using it as a goal, stay active and the slimming happens. Keeping up with your active minute goal daily is the key to long term success. A pound or pound and a half a week is outstanding/healthy weigh loss - great work!

[FoldingBikeman]

Before I purchased my Aria 2, I estimated my body fat using the YMCA formula which surprisingly tracks close to my Aria 2.  It only requires your weight in pounds and waist in inches. The formula for a women is: ( -76.76 + 4.15waist - 0.082weight ) / weight

the formula for a man is: ( -98.42 +  4.15waist - 0.082weight ) / weight

[elderwanda]

It seems to me that the YMCA method could be way, way off.  You could have three women, each 150 pounds with a 30" waist.  One is tall and muscular.   Once is short and fat and/or muscular.  One is very short and has a whole lot of fat on her butt & thighs, but relatively little around the middle.   I can see how they could be something like 25%, 35%, and 45% respectively.  With a thirty inch waist, it's unlikely that any of them are very low body fat, but it certainly would vary enough to make the formula pretty much useless.  

Maybe I'm wrong.  Personally, a DEXA scan (and the Aria) puts me at about 35%, and the formula puts me at 33%, which I guess isn't too far off.  

[FoldingBikeman · Accepted solution]

I too was very skeptical of the formula as well. After all, most of the more extensive formulas used calipers and measured multiple parts of the body and combined them using more a complex method. What I found was they just didn't seem to make much difference. I suspect the reason is the waist circumference is much more significant than the other body parts. I am sure there are exceptions but when you consider the error rates of all the body measurement techniques, the YMCA formula provided a useful measure over time that was really easy.  I use the aria 2 now, not because of its accuracy, but because of its convenience. I actually get a higher variation with the scale even though I measure myself every morning about the same time. Over time though, they both seem to track reasonably close.