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There are some things in life that when they’re around we wish they weren’t there and when they’re gone, we’re just glad that they left. For many of us, one of those things is fat. But your fat tissue is full of important biological molecules called lipids – long and stringy compounds of hydrogen, carbon and oxygen that are great at storing energy in their chemical bonds. When the molecules are broken apart they release the energy stored in their bonds. We often refer to this process as “burning fat”. But when you “burn fat” where does that material – the actual stuff that jiggles around and cushions you and insulates you – where does it go? Interestingly enough, a recent survey of doctors, dietitians and physical trainers revealed that even the experts in fat loss didn’t know the answer.






Although they thought they did. More than 50% of the respondents thought that when you burn fat, all that mass is simply converted into energy and lost as heat. It’s a common misconception, but it’s not possible. I mean just because you don’t like something doesn’t mean that the laws of chemistry don’t apply to it and one of the basic principles of chemistry is the conservation of mass. This just means that the same amount of material always comes out of a reaction as goes into it. Even if that reaction happens to generate heat, you’ll wind up with the same number of each kind of atom that you started with. So, when you break up those lipids in your fat cells and release their energy all of that hydrogen, carbon, and oxygen in those molecules will still be there afterward.

But if you burn a lot of fat, and it’s not there anymore to hold your pants up or whatever, where did the mass go? Turns out, you exhaled it. Biologists at the University of New South Wales recently did an atom by atom breakdown of where the mass of your fat goes after it’s burned in your body. They found that for ever ten kilograms of fat that you burn, you have to inhale 29 kilograms of oxygen to metabolize or break down the fat and release its energy and the process of breaking down that much fat produces 28 kilograms of carbon dioxide and 11 kilograms of water. So for every kilo of fat that you burn in your body, more than 80% of that mass is lost as carbon dioxide that you breathe out. The other 20% you lose as water in your urine or sweat, or depending how hard you work out, your tears but if you do the math, you will see that all the mass in that fat-burning reaction has been conserved. 10 kilos of fat plus 29 kilos of oxygen equals 39 kilos total And together they produce 28 kilos of CO2 plus 11 of water which also equals 39 kilos.

So remember that the next time you’re huffing and sweating on a treadmill, or walking your dog, or really doing anything that makes your body call on its energy reserves, you’re basically just emanating fat through your breath and your skin, but in a good way.


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