# When you lose weight, how does the mass exit your body?

As a thought experiment, consider the case of Angus Barbiery, who allegedly lost almost 200kg in about a year by not eating at all, save for necessary nutrients provided as supplements.

My question is, where did those 200 kilograms go.

And please, don't suggest that it was "converted to energy". 200 kilograms of mass would be approximately equivalent to 1.8*1016 joules. For comparison, Czech nuclear power-plant Temelín generates approximately 4.3*1016 joules of energy.

So how does the mass exit the body after the glucose is metabolized?

• I suggest you consult a text book to find out the chemical products of the metabolism of glucose (or fat). Then blush and withdraw your question. – David May 13 '18 at 21:45
• Closely related/possible duplicate of: Breathing faster to lose more weight – fileunderwater May 13 '18 at 21:51
• To burn fat it needs to be aerobically. Cardiovascular exercise is critical...steady state heart rate 65 to 85% of max heart rate using large muscles. After 10 to 15 minutes, THEN one is burning fat. So holding onto that rate of exercise for another 30 minutes means major burning of actual body fat calories. Figure out how much you would be able to lose per day walking for an hour. Don't be discouraged, you are also changing your body to BURN fat more readily like a race car versus a volvo. People who are more muscle than fat NEED calories regularly. Fasting is just stupid and stupider. – stormy May 13 '18 at 22:22
• Nobody except you is suggesting that the human body is a nuclear reactor, so the strident tone in your question is unfortunate. And what is presented is a calculation, not a thought experiment. (You owe Schrödinger an apology, I think — or at least his cat.) Energy and matter may be interchangable, but before this was discovered there was a law of conservation of matter based on general everyday experience of how one form of matter is converted into another. – David May 14 '18 at 9:10
• @David I was googling this before asking and a great amount of people have written things like "he converted the fat to energy". The thought experiment goes before the calculation, hence new paragraph. – Tomáš Zato - Reinstate Monica May 14 '18 at 14:19