From this article at Nautilus:
You may think of yourself as a highly refined and sophisticated creature—and you are. But you are also full of discarded, rejected, and recycled atomic elements. Don’t worry, though—so is almost everyone and everything else.
The oxygen in your lungs and bloodstream is a highly reactive waste product generated by vegetation and microbes. Trees, herbs, algae, and blue-green bacteria split oxygen atoms out of water molecules during photosynthesis. They use most of the resultant gas for their own purposes, but thankfully some leaks out to sustain you. In fact it makes up about a fifth of the air you breathe. Your cells harness oxygen to release energy from chemical bonds in the food you consume. Oxygen absorbs electrons released by broken food molecules, which attract hydrogen ions, resulting in a molecular waste of your own making: metabolic water, which comprises one tenth of your body fluids. An average adult carries between 8 and 10 pounds of homemade wastewater within them, and one in 10 of your tears are the metabolic by-products of your breathing and eating.
All this waste is going to my waist.
Read the rest of the article here.