Digestion is the process your body uses to break down food into tiny particles that can be absorbed and used for energy, growth, and repair. When you eat an apple or a sandwich, your body can't use it in that form. Digestion transforms that food into molecules small enough to pass through your intestinal walls into your bloodstream, where they travel to cells throughout your body.

The journey starts in your mouth, where chewing and saliva begin breaking food apart. Your stomach continues the work with powerful acids that turn food into a thick liquid. Then your small intestine, helped by chemicals from your liver and pancreas, finishes the job of extracting nutrients like proteins, fats, and carbohydrates. What your body can't use continues to your large intestine and eventually leaves as waste.

The whole process takes hours, working automatically while you sleep, play, or study. Different foods digest at different rates: a piece of fruit might take an hour or two, while a steak dinner could take four to six hours. Good digestion depends on eating a variety of foods, drinking enough water, and giving your body time to do its complex chemical work. When digestion isn't working well, you might feel stomach aches, bloating, or discomfort.