Can a bathroom scale really measure body fat?

Public Comments

1. Yes, I have one. It works by sending small electrical shocks through your body (you can't feel them) to measure you body composition.
2. Yes, it's more of an electrical wave that you can't feel - the longer it takes to go 'through' you, the more fat you have. That's why you can't use them if you have a pace maker. You need to set if you are male or female and then set your height, step on (hold breath!), mine does a 5, 4, 3, 2, 1 and then tells me my body fat percentage and weight.
3. it isnt measuring body fat, how it works is that the electrical signal passing through your body from foot to foot is impeded depending on how much water is in your body, so it's really measuring you bodies water composition, however entering your height and weight (scales duh) allows the scales to 'estimate' from the impedence how much body fat you have as lean tissue and fat tissue contain different amounts of water. So if you just drank a load of water and got out of the shower dripping wet it's going to read different to if you havent drunk anything all day and just got back in from a 5 mile run, even though from those two scenarios your amount of fat wont have changed. They're usually accurate to within a few % either side though which isnt bad considering.