How Digestion Works

Presented by Dr. Mary Pardeep with Commune

Tags: digestion, food, gut, microbiome

“All disease begins in the gut.” – Hippocrates 

How Digestion Works

Image by Wikimedia Commons
  • Gastrointestinal (GI) Tract
    • Responsible for the digestion and absorption of food and fluids
    • Breaks food down into single amino acids, fats or glucose which are absorbed over the intestinal wall and made into energy by cells
    • Food converting into energy requires a healthy GI tract 
    • Is a long tube that runs from the mouth to anus 
    • Is a surface that communicates with the outside world
  • Step 1: Chewing your food
    • The only mechanical digestion we get (physical breakdown from the force of teeth to food)
    • The rest of digestion is chemical 
    • Food passes from the mouth to esophagus and then stomach 
  • Step 2: Stomach
    • A storage vessel that controls the rate that the contents move into the small intestine
    • Is very acidic – has a low pH level of 1.5 (water has a pH of 7, while a battery has a pH of 0) and is more acidic than lemon juice
      • Crucial for killing bacteria, pathogens and toxins that may have entered through food
    • Contains hydrochloric acid (HLC) and pepsin a digestive enzyme that helps to break down protein 
  • Step 3: Small Intestines 
    • Called small because of its diameter, not its length
    • Is 15-20 feet long 
    • Is where the majority of nutrient (vitamins, macronutrients, carbohydrates, protein, fats) absorption happens 
    • Contain villi which are finger-like projections that increase their surface area so that all of the nutrients we need are properly absorbed
    • When food mixture enters, it is made less acidic by digestive enzymes that are released from the pancreas and bile from the gallbladder
      • Enzymes break down chicken/protein into amino acids; 
      • Enzymes break down sweet potato/carbohydrates into simple sugars such as glucose;
      • Enzymes break down olive oil/fats into short chain fatty acids 
    • Bile: breaks down our fats so they can be absorbed by the body
      • Is produced by the liver and is stored in the gallbladder until it’s needed
      • If released ineffectively it can lead to diarrhea (i.e., the fats aren’t getting absorbed, speeding up the digestive process)
        • People who have had their gallbladder removed can experience digestive issues 
    • Acetylcholine: a key neurotransmitter of the parasympathetic nervous system (our rest and digest system)
      • If you’re not in a relaxed state when eating, then the proper amount of digestive enzymes won’t be released, resulting in food not breaking down efficiently
        • Can lead to symptoms such as: indigestion, acid reflux, diarrhea, constipation, bloating 
      • A lot of GI conditions are likely caused by a disruption of the nervous system
        • Low parasympathetic tone (i.e., constant states of fight-or-flight)
  • Step 3: Large Intestines (colon)
    • About 5 feet long
    • Where we absorb the rest of water to make solid stool
    • The speed of movement in the large intestines will determine the consistency of your poop (this matters):
      • If things are moving too quickly, not enough water is absorbed and can lead to loose stool/diarrhea 
      • If things are moving too slowly, too much water is absorbed and can lead to “rabbit pellets”/constipation 
    • The rest of nutrients are absorbed here 
    • Is the main storage container for the gut microbiome which is a community of bacteria, viruses and fungi that help us digest our food, make vitamins, modulate our immune system and more 
    • Food becomes poop and will make its way across the colon, through the rectum and in the toilet (mission accomplished!) 
  • The health of your gut can be determined by your poop

Learn more from Dr. Pardeep:

Introduction to Gut Health

What Healthy Poop Looks & Smells Like

The Brain-Gut Connection

Mindful Eating (Where Digestion Begins)

More from Dr. Mary Pardeep

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This website is provided only for informational purposes and not intended to be used to replace professional advice, treatment or professional care. Always speak to your physician, healthcare provider or pediatrician if you have concerns about your own health or the health of a child.