How can one person consist of 50% fat and 60% water? What about the rest?
In: Biology
Simple answer, fat cells contain water.
When they say body fat percentage they mean percentage of weight in fat cells, but those fat cells contain various other things.
You’re looking at two different composition analyses and trying to equate them. For the body fat percentage, that comes from an analysis of the percentage of weight made up from fat, muscle, and “other” (Bones, organs, skin, etc) So your percentages there need to add up to 100%.
For the water percentage, that comes from a molecular breakdown of the body. If you separated a person into their individual molecules, 60% of it would be water. The rest would be proteins and other cellular materials that need to be hydrated to function. Even bone is about 31% water, if you could chemically remove the water from the structure.
The percentage body water is not absolute. Its actually lower in people with morbid obesity. Doctors deal with this all the time. In fact, some drugs are based on ideal body weight. That’s where you take someones height and calculate how much they should weigh and then dose based on that.
You’re comparing 2 different categories of body %. It’s like saying Weed is 95% green in color yet it has 20% THC.
“x% water” is relative to molecules – it means x% of your mass are from water molecules.
“x% fat” is relative to tissues – x% of your mass is in fat tissue.
These two percentages are not mutually exclusive – fat tissue has a large proportion of water molecules too.
You’ve gotten a lot of answers answers here that are plainly factually incorrect. Like the top answer stating “fat cells contain water….. bf% = % weight in fat cells.” This is not true. BF% is literally the % of your body weight that is made up of lipids. Doesn’t matter where those lipids are. The myelin (insulating coating made of fat) on your nerves gets counted just like the triglyceride (fat) deposits in your adipocytes (fat cells). Nearly all of the highly upvoted answers are wrong, which is a bit strange. Like the whole “molecules vs tissue” thing. That’s just not right.
The whole “60% water” thing is an average for a person of relatively normal size. Most cells in the body are made almost entirely out of water. They’re basically bags of water with some stuff dissolved in it.
Fat cells are an exception to this. They do have SOME water, but it generally makes up a relatively small percentage of their overall mass. So, if you take a male with a healthy but not particularly athletic body composition, about 15% of his body mass will by fat. About 5% will be “dry” bone. Of the remaining 80%, most of that is made up of cells, and most cells are mostly water. So 75% of what’s left will be water, giving us 60% water.
A person who is 50% fat by mass would be dramatically overfat. Like fat enough that daily life would be difficult. They would not be 60% water, because as you’ve noticed, that would put us over 100%. Of their 50% of lean mass, we can guess that somewhere around 70% of that will be water. That would put them at around 35% water by mass.
Have you ever seen those little conductive body-fat measuring devices, like the ones gyms have that you grip, or the ones that have electrodes in a scale? Those “measure” your bodyfat percentage by seeing how well your body conducts electricity, using that to estimate what % of your weight is water, and working backwards to guess what % is fat. So if they find that you’re 60% water as a male, they’ll guess that you’re around 15% body fat. If they find that you’re 35% water, they’ll that you’re closer to 50% body fat.
TLDR/Extra Eli5: Your average adult young man is about 60% water. A tiny bit less for women.
Someone who is 50% fat is not average. They’re probably 400+ pounds. They do not have 60% water. They have less.
OP, I’d like to apologize on behalf of all of humanity for the clusterfuck that is the responses to this. I hope you found the answer you were looking for, because I came here for the same reason and I did not. BTW, if you did find an answer, could you explain it to me like I’m 5, please?
How can you be 100% human when you’re 60% water?
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