Quirks & Quarks

Why do we seem to generate so much poop?

The average human poop is mostly generated from water, while very little comes from undigested food waste.

Poop is mostly water and bacteria, rather than undigested food

The average, healthy human poop contains very little undigested food waste (Ollyy / Shutterstock)

Today's question comes from Jim Van Horn in Kaslo, British Columbia. He asks: Are the digestive systems in humans and animals that inefficient, or is it our diet that produces so much of the waste stream?

Emma Allen-Vercoe, a professor of microbiology and Canada Research Chair from the University of Guelph points out the poop is mostly not undigested food. About 75 per cent of the average human poop is water. Of the remaining 25 per cent, over half of that is bacteria from our gut microbiome. So only a very small amount is undigested food. So efficiency of digestion is not really an issue when it comes to volume of fecal waste.

The role of the bacteria in poop is important. In our gut, they help us break down food so it can be digested. But once they've left us, they also keep working as part of the wastewater treatment process. They work with microbes from the environment to help break down and remove impurities from sewage.

However, the contamination of wastewater by flushing chemicals down the toilet interferes with that process and the health of those gut microbes. So we can ensure the efficiency of wastewater treatment systems by making sure that our poops are healthy so gut microbes can do their job in the best possible way.

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