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What happens to food that the digestive system cannot use?

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Food that the human body cannot use or digest is processed as waste and eliminated through the digestive tract. After nutrients are absorbed in the small intestine, the remaining undigested material—which includes substances like dietary fiber—travels to the large intestine.1

In the large intestine, water and salts are absorbed from the waste, and the remaining material is compacted into feces. This waste consists of approximately 75 percent water and 25 percent solid matter, including dead bacteria, indigestible food particles, fats, inorganic substances, and cell debris.12

The waste is stored in the sigmoid colon and the rectum until it is ready to be expelled. The process of defecation involves muscular contractions that move the feces through the anal canal to be discharged from the body. This entire digestive process typically takes between 24 and 72 hours to complete.341