Stealing the sugar
So what of this solid brown mess can be burned to produce decent amounts of energy? Technically, burning anything produces energy, but some things produce more energy than others, and the amount of energy expunged depends on how efficient the combustion is.
Carbohydrates, many of which are found in poop, are made of carbon, hydrogen, and oxygen. Our body converts carbohydrates into glucose (sugar), which is primarily used to power cells. Ultimately, it is the high-energy-density glucose that we want here.
Carbohydrates also take the form of starch – many sugar units bonded together – and fiber, the latter of which only comes from plant-based foods. In the body, unlike other carbohydrates, fiber cannot be converted into sugar. Chemically speaking, however, if this fiber is made of cellulose (and much of it is), then it can be – it’s a type of polysaccharide, which means it's a molecule made of many interconnected glucose molecules.
However, almost all starch and sugar will be used by the body and not pooped out. Any glucose not immediately needed is converted into fat for long-term storage, and some is excreted as poop, but it cannot be converted into glucose again, and the body uses it as a fuel in a very different way. Conversely, dietary fiber isn’t digested by the human body, so all of that is excreted. For our poop combustion engine, then, we can use this expunged fiber.
So what proportion of our poop is made of fiber? Out of our 25 grams of solid matter per daily poop, as much as 30 percent is made of fiber. So that’s 7.5 grams (0.017 pounds).
Dietary fiber mostly comes from food like this. Credit: Oksana Shufrych/Shutterstock