GUT FEELINGS – Part 1: Digestion 101

In this five-part series, we’ll be talking about all things digestion. We’ll start with the basics of digestion before moving on to things that can go wrong, how stress affects digestion and harms your gut, the magical term ‘leaky gut’, and finally simple steps on how to heal your gut and optimise digestion.

Digestion is simple right? You eat your food, it gets digested in your stomach, slips and slides through your intestines and you poop it out the next day? Um… not quite…

Digestion can actually be a fairly complex process that involves much more than just your stomach and intestines. Firstly, it starts way up north. No, not your mouth… think higher. Digestion starts in your brain! Wait, what now?

Whether you realise it or not, you start digesting your food WAY before it even reaches your mouth.

Think about your favourite cheeseburger: a succulent beef patty sandwiched between layers of melted cheese and a good slathering of secret sauce, topped with fresh crunchy vegetables and finished with fluffy, buttery brioche buns. Are you salivating? Yeah, me too (note to self: don’t write when hungry).

See, your brain is already sending signals about this food that you’re potentially going to eat! It’s preparing your mouth to start chewing- hence the saliva- and I bet your tummy is starting to rumble a bit too, getting ready for the food to enter.

When you finally take a bite of the cheeseburger, your mouth begins the mechanical breakdown of the food (i.e. chewing) while enzymes in your saliva break down the carbohydrates in the meal.

As you swallow, the cheeseburger (now called a bolus) travels down your oesophagus, past the cardiac sphincter (something like an automatic swing door) and into your stomach.

In the stomach, gastric juice is secreted from millions of tiny glands that line the stomach. In it you’ll find mucous, pepsinogen, and hydrochloric acid (HCl). HCl plays an immense role in the stomach: it baths the stomach, killing off any bacteria and parasites that we could have ingested; it also activates pepsin, which breaks down the proteins in the food. The bolus, now churned with gastric juice, becomes a very acidic paste called chyme.

The chyme is released into the upper part of the small intestine, the duodenum. The acidity of the chyme triggers the small intestine to secrete mucous to protect itself from acid burn, at the same time two other hormones are secreted into the bloodstream: secretin and cholecystokinin (CCK).

Secretin stimulates the pancreas to release bicarbonate (yes, the same one as in sodium bicarbonate) to neutralise the acidity of the chyme, while CCK makes the gallbladder release bile, which is necessary to emulsify and absorb fats in your meal. Pancreatic juice is also released to complete the digestion of carbs, proteins, and fats.

Having a healthy small intestine is key because this is where all the nutrients from your food gets absorbed into your bloodstream to be used by the rest of your body.

90% of your immune system also resides here, protecting you from foreign microbes and signalling to the rest of the body to attack these invaders. Unfortunately the sensitive lining of the intestinal wall is easily compromised, leading to ‘leaky gut’, which we’ll get to at another time.

Finally, the leftover chyme from the small intestine (indigestible fibres, bile, water, etc.) get passed on to the large intestine through the ileocecal valve.

The large intestine is the home of all the beneficial gut bugs that everyone talks about these days. The good bacteria capture any nutrients that are still available and convert them into vitamins K, B1, B2, B12 and Butyric acid, a fatty acid that is the primary fuel for your colon cells. The large intestine also recycles water and waste material, which nourishes the colon cells, and of course it forms and expels waste.

As you can see, there are tons of things that happen in your gut besides just swirling food around in your stomach and forming waste. So many processes happening means more things that could go wrong… yikes!

Stay tuned for Part 2 of the Gut Feelings series to learn more about dysfunction in your digestive system!

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