The Large Intestine – How Digestion Works

The large intestine is your food’s last stop before elimination. That means we’re talking about poop today! It also means that this is the last post in our How Digestion Works series. I cannot wait to get into it! The large intestine continues the work of your small intestine, but it also does a few extra things that the small intestine doesn’t do.

The large intestine (or colon) is divided into five parts. The ascending colon, the transverse colon, the descending colon, the sigmoid colon, and the rectum. The entirety of the large intestine measures about 5 feet long. The chyme will move from your small intestine and into your colon through your ileocecal valve. At this point in the digestive process, very few nutrients remain. The ascending and transverse colon absorb potassium, sodium, and water. The wealth of bacteria found in the large intestine feed on the fiber in the chyme and produce vitamins and other helpful substances that are then absorbed throughout the large intestine.

The transverse colon finishes forming the chyme into stool and pushes it down the descending colon into the sigmoid colon. The remaining bile acids are reabsorbed into the bloodstream to be reused at this point. A lot of bile acids are reabsorbed by the ileum of the small intestine, but the large intestine finishes the job. The sigmoid colon contracts and releases to build up enough pressure to push the stool into the rectum. The rectum will hold the stool until there is enough to have a bowel movement. At that point, it releases the stool through one of two sphincters. This first sphincter is involuntary. The pressure of the stool on our second sphincter triggers the urge to relieve ourselves. We have control over this sphincter and can choose to hold the stool in until we get to a toilet.

The Microbiome

Inside of your large intestine, there are billions of little bugs called bacteria. In fact, throughout your intestines, there is estimated to be about 1 million bacteria per square millimeter and it weighs about 2kg (4.41 lbs) altogether. Some of these bacteria are helpful and some are not so helpful. The bacteria is often sorted into two camps: “good” bacteria and “bad” bacteria. Don’t get too hung up on the words good and bad. Regardless of how you eat and live, you will have a mixture of both and that’s perfectly normal. The bacteria, along with other microbes like fungi and viruses, is collectively called the gut microbiome.

Most organs have some version of a microbiome. Bacteria live almost everywhere. The microbiome of your skin, for instance, has become a popular topic among skin care enthusiasts. Microbiomes always have a combination of good and bad bacteria. The goal for any human is usually to have enough good bacteria to be able to keep the bad bacteria from causing any issues. You will have both and that’s okay and normal, but an overgrowth of bad in the large intestine can cause digestive issues, affect the brain, cause food cravings, and even cause disease.

The unique thing about the gut microbiome is that all the little bugs will feed on the food that we eat. They eat (or ferment or decompose) food that we can’t digest on our own, like fiber-rich foods. After they eat, they produce different chemicals and molecules that your body is then able to utilize. These include:

• Vitamin B12
• Vitamin B5
• Vitamin B1
• Vitamin B2
• Vitamin K
• Short chain fatty acids like acetates, propionate, and butyrate

This is what is referred to as a symbiotic relationship, which just means that both you and the microbiome both benefit from cohabitation.

Too much bad bacteria can crowd out good bacteria and vice versa. You will never be able to completely eliminate bad bacteria, but you can help prevent overgrowth of bad bacteria by feeding the good and limiting how much you feed the bad.

Things that feed bad bacteria are:

• Refined sugar (or any sugar…but we’ll talk more about that below)
• Artificial sweeteners
• Meat that has been regularly treated with antibiotics
• An abundance of fatty meats (bacon, pork rinds, ribs, prosciutto, etc.) and cheese

Things that feed good bacteria (also called prebiotics) are:

• Vegetables
• Fruits
• Nuts
• Legumes
• Eating a lot of different foods (the more types of food you eat, the more diversity of bacteria you will have)

Foods that contain probiotics (or good bacteria) are fermented foods like:

• Plain yogurt
• Kimchi
• Sauerkraut
• Kvass
• Fermented veggies
• Kefir

But Emma, you just put all the yummy foods on the bad list and all the boring ones on the good list. I know, just hear me out. Luckily, most people don’t have to completely cut out the top list. It’s all about balance. You can have bacon and sausage for breakfast, but maybe try for a salad with salmon for lunch and grilled chicken fajitas for dinner. You can also absolutely learn how to make the bottom list truly delicious with a couple cooking classes and/or some recipe hunting. My fellow NTPs, Christina Curp at The Castaway Kitchen and Allison Marras at Food By Mars both have a wide variety of delicious recipes to choose from on their websites.

You will also notice that I put fruits on the list of foods that feed the good bacteria even though I said any sugar feeds the bad. Fruits contain both sugar and prebiotics. They also have plenty of nutrients and are usually fairly easy on the digestive system. The wins definitely outweigh the losses in this case. I am all for fruit as part of a balanced diet. I am also not opposed to raw honey which is another whole food that contains nutrients. Honey does have antibacterial properties (it’s often used medicinally), so, be careful and go easy with this one. Sugar is not “bad.” We actually need glucose to function properly. The problem is that we eat way too much of it. My general recommendation is to find a nutrient dense, whole food way to curb your sweet tooth.

Just like in humans, frequent antibiotic use can create antibiotic resistant strains of bacteria in animals. When you eat meat that has some of these resistant strains of bacteria, it can transfer to you. Your best bet is to go for organic, grass-fed meat when possible.

Many people will supplement good bacteria with probiotics (which are basically good bacteria in pill form). This can be beneficial for a little while if you have an imbalance in your microbiome. Just remember that there is no point in taking probiotics if you are not also eating plenty of prebiotics to keep them alive and healthy in your gut. You can also get probiotics from the food sources listed above.

Microbiome research is still relatively new and there are plenty of questions that we don’t have answers to. Nevertheless, it’s important to be aware and do the best you can with the info we have. Ultimately, a wide variety of nutrient dense whole foods should be the foundation of your diet.

How Northern Digestion Affects The Large Intestine

The brain and the intestines talk to each other all the time. The microbiome in your large intestine has a big impact on your mood and mental health. There have been several recent studies that have found an imbalanced gut microbiome in people who struggle with things like depression, anxiety, autism, and bipolar disorder. Several people who struggle with mental health have noticed improvements when they make dietary and lifestyle changes that support the gut and the gut microbiome.

Check out the previous How Digestion Works posts to learn more about the upper digestive system:

The Brain And Mouth – How Digestion Works

The Stomach – How Digestion Works

The Liver – How Digestion Works

The Pancreas – How Digestion Works

The Small Intestine – How Digestion Works

You get to control how long you chew your food. 30-40 chews per bite is what is recommended, but really, it’s however long it takes to get your food to a smoothie-like consistency. If your food is already a smoothie-like consistency (applesauce, smoothies, yogurt, etc.), chewing a few times is still ideal. This is because chewing thoroughly also gives your brain time to stimulate digestion in the stomach and for the enzymes in your saliva to mix with your food and start to breakdown carbohydrates and fat. Food that is not thoroughly chewed is harder for the rest of your digestive system to breakdown.

After traveling down your esophagus, your food (which is now called a bolus) arrives in your stomach. If you have chewed well and were relaxed and focused on your food while eating, the stomach should already has a mixture of digestive juices waiting for it. The bolus is mixed around in the stomach for 1-2 hours. During this time, enzymes continues to work on breaking food particles down chemically, and stomach acid disinfects your food to help prevent infection down south. Stomach acid also helps with the digestive process by relaxing some of the proteins and making it easier for the protein splitting enzymes (protases) to work. Alcohol and some drugs are absorbed here.

Slowly, the bolus is released into the small intestine and becomes chyme. This happens over a period of about an hour. Carb heavy meals will be let into the small intestine quicker and a fat heavy meal will take the longest to exit the stomach. The duodenum is the first section of the small intestine. When acidic chyme enters, it triggers a couple hormones called CCK and secretin. These hormones trigger the release of bile and pancreatic juices. Bile is created in the liver and stored in and released from the gallbladder. Bile is a dark yellow, soap-like solution that emulsifies fats.

Pancreatic juices are created and released by the pancreas. It is made up of bicarbonate and digestive enzymes. Bicarbonate is highly alkaline and it neutralizes the pH of the chyme so it doesn’t burn the inside of your small intestine. Pancreatic enzymes continue to breakdown food throughout your small intestine.

All three sections (duodenum, jejunum, and ileum) of the small intestine absorb specific nutrients. Peristalsis is the act of the muscles of your digestive tract contracting and relaxing to push your food through your digestive system. It also mixes the chyme which helps further digest food particles. The small intestine also has some microbes that help ferment and breakdown food particles that we couldn’t otherwise digest. The wall of the small intestine is full of folds, protrusions called villi and microvilli, and mucosa. All of these components help you digest, absorb, and protect your body. The actual gut lining in the small intestine is just one cell thick. This lining acts as the barrier between pathogens, bacteria, and undigested food, while letting nutrients in.

The large intestine is where the final nutrients are absorbed, the microbiome truly shines, and stool is formed. This is how this process is supposed to work. However, if your have read any of the previous posts in the How Digestion Works series, you know that a lot can go wrong before your meal even hits your large intestine. Any dysfunction that happens north of the large intestine affects the large intestine’s ability to do its job well and can even harm the large intestine itself. Stress and distractions while eating, gulping food down in the car on the way to work, eating mainly simple carbs with little to no fat or protein, insufficient pancreatic enzymes, leaky gut, eating the Standard American Diet (SAD), and little to no movement during your day can all hurt your digestion.

Stool: Your Daily Health Check

It will never be glamourous, but checking your stool can provide you with useful information. Your stool can tell you so much about the state of health your body is in. Stool can be different colors, textures, smells and they can come at varying times. Let’s start with colors:

• Dark/Medium Brown: This is the normal color of stool. The dark yellow color of bile is actually what gives stool this brown color.
• Pale/Light Brown, Gray, or Yellow: I will usually look for other signs of liver or gallbladder dysfunction when I see pale stool. These colors could mean that your stool was not in contact with bile for as long as normal or there was less bile excreted.
• Green: This color is almost never something to be nervous about. It usually means that you’ve eaten a lot of dark green foods like veggies or green food coloring and the pigment is showing up in your stool. However, if your stool is like this for a prolonged period of time (a few weeks or longer), consider seeing a doctor just to be safe. Persistent green stool could be a sign of dysfunction in the digestive tract.
• Red: There are a couple reasons your stool may be red. You could have eaten food with a strong red pigment like beets in which case, it’s nothing to worry about. It could also be blood…which is usually something you should worry about. If you continue to have blood in your stool, you need to contact a doctor. Check to see if it’s bright red or dark red and if it’s mixed into the stool or just covering it. Your doctor will want to know.
• Black: This color is similar to red, in that it could be completely fine or it could be blood. Iron supplements will turn your stool black. Black blood often suggests there is bleeding further north in the digestive tract. If you are not taking an iron supplement and your stool continues to be black for more than a week or so, you should see a doctor.

Texture and the frequency of your bowel movements often go together. There’s a handy chart called the Bristol stool chart that’s shown below. This chart is used to help clients and patients identify the texture of their stool to their practitioner and/or doctor. The lower numbers have sat in your large intestine for more time than they should while the higher numbers went through the intestines too fast. It’s ideal to have a number 3 or 4.

I have a side note for all my people who have struggled with constipation or diarrhea: If you find yourself struggling with the opposite problem…that’s not good either. I have Ulcerative Colitis. When I finally stopped struggling with diarrhea, my body went hard the other way. I would have 1 bowel movement a week, but I didn’t care. I was just so happy to not have to rush to the bathroom all the time. When you have diarrhea, you aren’t absorbing nutrients like you should. When you’re constipated, you’re absorbing nutrients but your also absorbing toxins due to how long the stool sits in your intestines. Neither of these options are good. Luckily, you don’t have to choose one!

Many people can find relief from both of these issues through diet. Even if you’re like me and have a diagnosed condition, diet changes make a huge impact on your health, symptoms, and they can support specific systems in your body that are contributing to your diagnosis. In my case, I was able to find foods that both promoted mobility and didn’t trigger a flare up. I also shifted some lifestyle habits that also helped me keep my stool regular like gentle to moderate exercise, deep breathing, resting when I need to, and staying hydrated.

Your stool will never smell like flowers. Sometimes, you might notice that your stool smells worse than normal. This is not usually something to be concerned about if you have no other symptoms. It’s common for stool to give off a rotten egg or sewer gas smell when you eat a lot of foods that contain sulfate. These foods include broccoli, cauliflower, cabbage, and eggs. If you are having other symptoms, then you should start investigating. The smell of your stool alone will almost never give you the answer to what is causing dysfunction.

Many people will hold in their stool for a prolonged period of time. However, the longer the stool sits in the colon, the more water is absorbed from it. This means that by the time you decide you’re ready to have a bowel movement, it may be much harder to pass.

Practical Dietary and Lifestyle Changes To Support Your Large Intestine

• Eat a wide variety of properly prepared, nutrient dense, whole foods
• Focus on supporting northern digestion
• Eat plenty of high fiber vegetables
• Stay hydrated
• Try to incorporate some gentle movement into your day
• Eat probiotic and prebiotic foods
• Eat plenty of good fats (cold pressed, organic olive oil, coconut oil, avocado oil, avocados, sesame oil, olives, raw nut butters, grass-fed dairy, etc.)

First and foremost, we need to be getting all the nutrients we need. This is essential for basic cellular health. The wider variety of high quality fats, organic fruits, and organic veggies you can eat the better. In fact…I have challenge for you. The challenge is this:

Find ONE vegetable you’ve never had before and eat it.

That’s it! You can have so much fun with this challenge by finding fun recipes and getting your kids or grandkids involved if you have them. If you have truly tried every veggie at your store, then look for a fruit, herb, or spice. The point is to add variety to your diet. This helps grow the diversity in your microbiome and it could add in some nutrients that you may not have been getting much of previously.

Gentle movement can massage the internal organs and help with mobility. Hydration helps with constipation, but is also extremally important when you have loose stool. Loose stool (or diarrhea) means that you aren’t absorbing as much water. Be sure to get plenty of quality water with electrolytes (you can add a pinch of quality sea salt to your water to get electrolytes).

Probiotic and prebiotic foods are listed above in the microbiome section of this post along with the foods that feed the less desirable microbes in your large intestine.

Summary

The large intestine is a pretty incredible organ. It houses much of the gut microbiome, absorbs remaining nutrients, and forms stool. However, it will only be able to do its job well if the organs above it in the digestive tract do their jobs. When I notice large intestine related issues with my clients, I always look at northern digestion first. Often, they also have dysfunction in the small intestine, stomach, and/or are dealing with a high level of stress and distraction during meal times.

The best place to start is to make sure you are eating a wide variety of whole, nutrient dense foods. Ultra processed foods should not have a place in your diet. The ingredients in these foods contribute to disease (additives, bad fats, and high levels of processed sugar) and they do not contain many nutrients. If you are still having digestive issues or are not meeting your goals once you crowd out these foods with nutrient dense foods, you should consider working with a nutritional therapy practitioner. NTPs are trained to evaluate your nutritional needs and create personalized diet and lifestyle recommendations that get you closer to your goals. You can schedule a free discovery call with me here or (for my introverts) email me: [email protected]

I hope you enjoyed learning more about the digestive system. Let me know what you learned down in the comments! I love the digestive system so much and I’m always down to talk about it, so if you have questions or observations, let me know down below!

I wish you all a beautiful week!