The FastDay Forum

I'm quite interested in the way in which fat % changes as we age and the assumptions made in body fat measurement scales. If I put my age in as 21 my fat percentage is 30.7, yet if I put my true age in the reading is 37.8. I have lost about 6 lbs, from 172 to 166 and expected my fat % to decrease, but it still sees to stay roughly the same, fluctuating between 37.4 nd 37.8%. Comments would be appreciated.

If you lose weight by dieting you would expect the %fat to reduce and the scales to reflect that.

The age thing is probably used in a mathematical formula o convert the electrical readings, weight and other data into %fat.

I posted this on another forum regarding fat content and aging


I found this explanation regarding the acceptable increased fat as you age
"You may have noticed as your age increases, your acceptable body fat within these ranges increases as well. Why you ask? In short, these charts are based on statistical assumptions. Older individuals tend to have a lower body density for the same skinfold measurements, which is assumed to indicate a higher body fat percentage. Older, athletic individuals, however, might not fit this assumption because their body density may be underestimated.

Digging a little deeper, there are 3 types of fat: subcutaneous (under the skin), visceral (around the organs), and intramuscular (in between muscle, like a marbled steak). The amount of subcutaneous body fat you have may stay the same, but the visceral and intramuscular fat may increase as you age."

I got out my calculator & worked out that as the scales always show that my fat % and water % always total 71%, if I was 170lbs and 37.8% fat I would be made up of 64.26lbs of fat, 73.44lbs of water and 32.30lbs of 'other'. If on losing 5lbs my fat% went down to 37.4 then I would be 61.71lbs of fat, 71.94lbs of water and 31.35 lbs of other. I would have lost about 2.5lbs of fat, 1.5lbs of water, and 1lb of other. I'm probably expecting too much from my scales! I might work out the weight I need to lose to get down to a healthy fat% for a woman of my age...but it's stopped raining so I'm going out.

I'm hoping that my daily walk to work & back (total 3.5 miles), taking the stairs - I work on the 5th & 5th floors & in the basement, 3 sessions a week of resistance training, a bit of yoga and leisure activities such as cycling and kayaking will help to preserve my muscle mass. Perhaps I'll just set the scales to the age I was when I weighed 140lbs!

At 28 BMI you weigh 1/3rd more than a lean version of you. If the lean version was 20% fat then you'll be around 38-40% fat.

Thanks for the tip about the website, KENCC. The calculator gives me a body fat%age of 25.2 which is considerably better than my scales which give just under 30% and that without me resetting it from my age about 4 years ago. I am pretty fit and everyone tells me I look really slim but I have a very slight build and still have a good covering of subcutaneous fat so am not getting too complaisant yet.
I plan to continue to lose around half a pound a week until subcutaneous fat looks about right, and exercise to keep it spread around as much possible.
As I have been using my scales reading on the Progress Tracker, will continue to do so for now.

Took you advice, kencc, thanks once again, and it put me in the middle of the healthy range at 21.1 which is just a touch higher than the 20.9 that the Progress Tracker gives me. Not planning to lose much more and aiming for 28" waist rather than worrying too much about percentages, hoping exercise will help achieve this. Still want the health benefits of fasting so will probably do one strict fast day and one "no treats, no booze and eat carefully" day.
Not planning to join US Army just yet

Thank for your replies, everyone.

The the body fat calculator is very interesting, kencc. My current body fat worked out at 36.4% on this, and my body fat at the start of this WOE worked out at 38.1%. My scales show no significant decrease over this time. However, I am not the typical female pear shape and I would expect to carry more fat than a younger female of my height and weight.

I suppose what it boils down to is that any of these methods give an estimate and should only be used as a guide. I think I will just focus on getting the weight down. I will continue to record the fat % reading from the scales when I update the progress tracker, which I now intend to do just monthly.

Here are my BF %ages using three different methods:
28.8% - my scales
25.2% - website giving calc US Navy uses, as posted by Kencc
37.7% - caliper test at gym
So I am anything between super-fit and obese!!!!!