The Student Room Group

Body Fat Scales

Hi, sorry this is a lot like a the 'what's your body fat %' thread but different! I am a bit overweight (bmi about 24.5 but I know full well that ain't muscle!) and recently bought some body fat scales. The instructions came with it said that above 33% body fat for women of my age group (under 25 i think) is overfat (can't remember what the obese limit is) although on the other thread it said over 32% is obese.
I tried to calculate my body fat online but it only asks for waist measurement and doesn't seem very accurate.
By my scales I am usually between 33% and 36% body fat.
Does anyone know how they work or how accurate they are? How can scales tell what's fat and what's not?
I think they work by putting a slight electric charge through your body and then back again, and then uses the amount of resistance in your body tocalculate the amount of fat you have. I'm not sure about it though.
Reply 2
Very inaccurate. That said, theres no particularly accurate version of measuring bodyfat, a combination of many methods is best.
Reply 3
haha i remember they actually did some fat testing method at pe class back in school.. it was basically this large pair of scissor type things without any actual blades, merely some ruler thing which worked out how fat you were.

also, 24.5 isn't overweight, so don't worry too much, though i suppose it is pushing the boundary.
Reply 4
silence
haha i remember they actually did some fat testing method at pe class back in school.. it was basically this large pair of scissor type things without any actual blades, merely some ruler thing which worked out how fat you were.

also, 24.5 isn't overweight, so don't worry too much, though i suppose it is pushing the boundary.


You mean with calipers?
Reply 5
that would be the one
Reply 6
I think the scales are alright - I bought some Weight Watchers ones for £60 mainly for the bodyfat thing. It gave me 13%, which was the same as what I calculated myself. Yet to use the calipers though.
remember that girls naturally have lots more body fat than boys- even if they're thin.
Reply 8
Lucyvet2006
Hi, sorry this is a lot like a the 'what's your body fat %' thread but different! I am a bit overweight (bmi about 24.5 but I know full well that ain't muscle!) and recently bought some body fat scales. The instructions came with it said that above 33% body fat for women of my age group (under 25 i think) is overfat (can't remember what the obese limit is) although on the other thread it said over 32% is obese.
I tried to calculate my body fat online but it only asks for waist measurement and doesn't seem very accurate.
By my scales I am usually between 33% and 36% body fat.
Does anyone know how they work or how accurate they are? How can scales tell what's fat and what's not?


Yeah these things send an electric current up one leg and back down the other leg and then measure the resistance which is then converted into a body fat %age. The measurement of resistance is pretty accurate, the conversion to body fat %age relies on a lot of assumptions. Basically muscle is much lower resistance than fat so if you have a higher resistance then this implies you have more fat. The assumptions that these things work on are:

Your body has average proportions - if your legs are longer than average for your height then the electrical path will be longer and so have higher resistance giving an incorrectly high body fat %age.

Your body fat distribution is average - the scales are only sensitive to body make-up in your legs, pelvis and lower abdominal area. If you're 'top heavy' then the %age output will be an underestimate, if you're pear shaped then it will be an overestimate.

You are fully hydrated - resistance is also influenced by water retained in your body, if you're dehydrated (e.g. just after exercise, or the morning after a night on the beers) then the fat %age will be incorrectly low.

Obviously the 1st 2 assumptions are not valid for a lot of people - hence comparing the %age a scale gives between 2 people is pretty much meaningless. However, if you use the same scales on yourself at different times then the assumptions are the same between the 2 times. What I'm saying here is if the scales say you're 35% fat on one day and 30% fat on another then you have lost fat between these 2 days.

The danger with this is the final assumption - the bit about hydration. Obviously hydration levels vary through the day depending on what you're doing so it is possible to get misleading readings. I would imagine as well for girls the amount of water retained at different stages of your period might also affect this. What you want to do is try to remove this effect as much as possible - then you can monitor your body composition. I did this by making sure I weighed myself in as constant a state as possible - just after I'd woken up and had a piss. When I did this the readings I got out were remarkably constant and any change could be explained by what I'd been doing in the previous few days (increased activity led to fat % going down etc.). The only time readings were off was on the morning after I'd been out on the piss the night before.

Hope this helps.