Digestion Posted on 21 Feb 15:57 , 0 comments

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By Todd Lee M.D. Instagram


Who am I? Click here for my Bio!




Do you have a mouth? Sure, we all do! Do you want to know what happens after digestion when you put things in your mouth? I bet you do!.

For simplicity we will pretend food is made up of four things: fat, protein, carbs, and vitamins/minerals.  Each of these things are digested and absorbed differently in different places in your Gastrointestinal (GI) tract.

The Mouth

As food enters your mouth carbs are the first to get digested. Human saliva contains amylase, and enzyme which digests carbs. If you put bread in your mouth it will quickly turn sweet as the amylase breaks the carbs down and they turn into simple sugars which bind to the sweet receptors on your tongue. This causes hormones to get your pancreas ready for the carbs when they get into your blood stream. Insulin is released in preparation to transport the carbs to the organs of your body.  The sugars can be absorbed through the lining of your mouth (mucus membrane) and all throughout your GI system.  When the carbs hit your bloodstream the insulin opens up the organs through GLUT receptors. Adipose tissue (body fat)  and muscle use the same receptor: GLUT4.

The Esophagus

Not much happens here except some passive diffusion across the mucus membrane.  There is a false sphincter where the stomach meets the esophagus.  If this is loose or if intra abdominal pressure is high then stomach contents can squirt up from the stomach to the esophagus while the stomach churns food.  This is one way heartburn occurs.

The Stomach

This is where the magic happens.  The stomach is super complex and majestic in its ability to reduce almost any organic material to nutrient rich mush.  I can't get into all the autocrine, intracrine, and paracrine functions of the hormones and neurotransmitters of the stomach here.  To give you a hint of its complexity, the stomach and the intestines have their own nervous system: the enteric system. Ever wonder why nerves gives you butterflies in your stomach?  Many of the neurotransmitters In the brain have specific functions in the GI system and that's why anxiety may manifest as stomach pain or Irritable Bowel Syndrome.

The super duper simple version is this: food enters the stomach and based on its contents several things may happen.  If it is 92% liquid, then it begins to be absorbed through the mucus membrane and it passes through the pylorus into the duodenum.  If it is over 8% solute and it has a significant amount of fat then the pyloric sphincter is closed and the contents can't leave the stomach.  This is through a very complicated paracrine process.  If protein is present then HCl is produced by the stomach, again a very complicated process. The stomach churns the food + acid mixture for as much as 6 hours before the pylorus opens to let the mush bolus through to the duodenum.

This is why your post workout nutrition should be a shake or Battle Mead that is 92% water. Then it is absorbed through the mucus membrane throughout the whole GI track and can deliver the pre digested nutrients like amino acids and simple carbs to your blood so insulin can carry it to your muscles within the first hour.  And the next meal should not contain any fat so the pylorus does not remain closed, this will allow your food to be digested and transported to the blood fast.  Often man-made foods like chocolate, alcohol, fried foods, and things that are spicy can cause an overproduction of stomach acid.  This results in heartburn.

The common approaches are chewing tums or rolaids, which buffer the acid, or taking a Proton Pump Inhibitor.  This causes the proton pump which dumps HCl into the stomach to break down and the pancreas just produces more gastrin over stimulating the stomach. The decreased acid results in the protein in food not being fully denatured. This means it may not be broken down and absorbed right once it passes to...

The Small Intestine

After the mush passes through the pylorus it makes it to the small intestine.  The small intestine is made up of 3 parts: The duodenum, the jejunum, and the ileum.  The duodenum is first and super complicated, it is where the bile and pancreatic enzymes meet the mush from the stomach.  This mixture is now called chyme.  The acid denatured protein is chopped up by the pancreatic enzymes to make amino acids which can now be transported across the jejunum and ileum lining which is made up of villi. Fat, the remaining carbs, and vitamins and minerals are all absorbed in the small intestine as well.  Digestive enzymes are an available supplement to help with digestion.  Papain, bromelain, and lactase are examples. For instance if someone is lactose intolerant then they don't make the enzyme lactase. Lactase cleaves lactose into glucose and galactose. When this digestive enzyme is taken as a supplement the person is better equipped to digest dairy.

Villi are like little fingers with lots of blood supply that stick out from the wall of the intestine. Gluten, found in wheat based foods, damages the villi and thus indirectly impedes absorption of many nutrients.  People will argue this. Those people love bread and other garbage and are in denial.  If your part cow maybe you can digest it, but no one needs it.

When nutrients are absorbed through your intestines it passes into the bloodstream of the GI system which all gets routed to your liver by the portal vein.  The liver attacks any drugs and tries to clear them since they are seen as toxins.

If you take supplements, and if you're reading this you probably do, then pay attention:  If your taking those supplements on a full stomach or with food their absorption is altered by the absorption of the food. They can chemically bond with the food or be modified by the stomach acid or food.  That's why there are 4 times when your stomach is empty, to take your supplements: First thing in the morning (Thor's Hammer),  pre workout (Fenris' Fury), post workout (Battle Mead), and right before bed. I have designed products with the right amount of the best ingredients for each of those times.

If you want to take supplements on a full stomach use a sublingual delivery.  This bypasses all digestion and the portal system and thus the liver. This drives bioavailability sky high.  Unless you need the liver to convert a drug or supplement to an active compound you’re always better off with sublingual delivery.

The Colon

This is really little more than a way for your body to absorb water and electrolytes from your feces. Any chyme that makes it this far wasn't digested and absorbed.  If your feces smells like something you ate than guess what, you didn't absorb it. Either eat less at a time or don't eat it at all. Once chyme makes it to your colon bacteria start digesting it.  This produces gas and that is where bloating and farting comes from. Another sign you ate something you shouldn’t.

Probiotic are not another name for digestive enzymes, despite popular belief.  They are live cultured bacteria which live in your colon and have a symbiotic relationship with you. These bacteria eat the fiber we can’t digest and often dairy and gluten...and all the food you couldn't absorb because your villi were to inflamed by the gluten you had to have.  If you're eating only foods your body can digest and absorb then you should be as regular as a dog.  15 g Psyllium Fiber before bed with 30 oz of water should ensure this.  Most commercial fiber products have sugar or say they don't and lie. You want to order straight Psyllium fiber.

You’re probably thinking; What about chylomicron absorption? The immune system? GIP? IgA? Food allergies? Nutritional absorption post gastric bypass? Pernicious anemia? Sorry Charlie, All those sub components are too complicated to add to one article. It would be a whole textbook if i went in-depth!


Nothing in this article or on this site should be considered medical advice or as an endorsement to violate any law of the country in which you reside.  The information given is for fun and entertainment purposes only.  All claims are 100% dependent upon proper diet and exercise.  Please consult a medical practitioner prior to any diet and exercise program.