is the density of a person change?

Question

we have a debate tomorow about this topic, please give me a complete answer or reference, thank you

Answer 1

Fat people are less dense, and you can see this because fat floats - or so I've been told. Apparently bone and muscle are more dense than water, fat is less dense than water.
Looking on a cycling forum I found somebody quote the figures:
Human body fat: 0.918 g/cc Human muscle: 1.049 g/cc
And they listed the references:
http://mb-soft.com/public2/bodyfat.html and
http://ajpheart.physiology.org/cgi/...full/278/1/H162 respectively.
Water has the density 1 g/cc and a litre has a mass of 1000g, a litre of fat would have a mass of 918g, a liter of muscle 1049g.
So if you train as an athlete, loose fat and put on muscle, your body becomes more dense as a result.
BMI (body mass index), where a high number is indicative of being fat is inversely proportional to a persons density. It is given by your size / mass, so a big size has a higher BMI than a small size with the same mass.
If BMI is given by size / mass, and density is given by mass / size, and the fatter you are the higher your BMI, then it also must be true that the fatter you are the lower your density.
The density of fat won't change, the density of muscle won't change, but if you consist of more high density material than low density material, you will have a higher (relative) density. i.e. you will be more dense.
When discussing density of fat and muscle, they are homogenous substances, i.e. they are entirely the same (any fat is fat, any muscle is muscle) and something which is fat or is muscle has only one density. A person is an object made up of multiple constituent substances, and has a volume and a mass therefore a person may have a relative density compared to another person, thus enabling the comparison of density between fat person and thin person. However, this density would not be uniform throughout each person, as they do not consist of a single homogenous substance. Also, the comparison would assume all of the things other than fat and muscle, such as hair and skeleton, were the same in both persons. And of course, temperature and pressure have been ignored.

Answer 2

Yes, I believe it does. Imagine 2 men, man A and man B, that weigh 250 lbs. each. Man A is fat and Man B is an athlete. Also, measure their waists, arms, and whatnot, and (try) to calculate the volume of each, or close enough. I would guess that man B would be quite a bit smaller than man A. But, as said previously, they both weigh the same, which makes muscle more dense than fat, and man B denser than man A. :D Do you follow my logic?

Answer 3

density is an intensive property meaning that it doesnt change. mass is extensive and it can change though your density will remain the same.

Answer 4

I think, yes