The Four Stages of Food Processing

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  • 0:00 Food Processing
  • 0:30 Ingestion and Digestion
  • 2:22 Absorption and Elimination
  • 3:57 Lesson Summary
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Lesson Transcript
Instructor: Artem Cheprasov
Did you know you are a walking, breathing, processing plant? In this lesson, we'll explore the four stages of food processing in your body: ingestion, digestion, absorption, and elimination.

Food Processing

Processed foods have a bad rap. Some experts say they are bad for us, and maybe so. However, I'm going to let you in on a little secret. And that is: all food is processed. All of it. It's processed by your body. Otherwise you wouldn't be able to derive any benefit from it nor be alive! There's more than one stage to the food processing performed by your body, and this lesson covers all of them.

Ingestion and Digestion

Let's walk into a restaurant together to learn about how our body, our processing plant, processes food.

I order a smoked salmon. Not having had any breakfast or lunch, I'm super hungry and so begin to ingest, or eat, the salmon very quickly. Ingestion is the first stage of food processing by the body; the act of taking a substance, such as a food or liquid, into the body by mouth.

Great, now I don't feel as hungry. But of course, I can't chow down on all of the salmon at once. I need to eat it one bite at a time.

But my body doesn't care. As soon as I put that first piece of food into my mouth, the process of digestion begins without waiting for me to finish the entire salmon.

Digestion is the second stage of food processing, the physical and biochemical breakdown of food by the body. By physical, I mean chewing and churning. As I chew the food, I physically or mechanically break it down into smaller pieces much like I would break food apart with a knife before putting the food into my mouth. My stomach and intestines also churn and squeeze this food with their muscles to further break it down physically.

This mechanical digestion breaks apart the food in order to increase its surface area for biochemical digestion. The salivary glands as well as the stomach and intestines secrete biochemicals that act like little scissors that break down the food at a molecular level into even smaller pieces of nutrients. This biochemical digestion allows for large particles like proteins, carbohydrates, and fats to be broken down into smaller constituents, small enough to be absorbed by the body.

Absorption and Elimination

At this point, after all the biochemical and mechanical digestion, the once solid piece of pink salmon on my plate is actually a gooey white slime in my digestive tract.

It is this gooey white mess of very small particles like simple sugars and amino acids that is then absorbed by the body. Absorption is the third stage of food processing; the taking up of end products of digestion from the lumen of the intestines and into the body. The lumen is the empty space within the intestines where food and feces can pass through. So when I say we absorb something, I mean we take it in from this cavity and into the body's cells, blood, or lymph.

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