Exercise & Digestion

Who else here loves exercise! I'm with you! I've been on both sides of the exercise spectrum (either not exercising at all, or exercising way too much), and I've found that my tendency toward overexercising, specifically with cardio/aerobic exercise, has contributed to some pretty nasty digestive symptoms over the years.

I never really considered how exercise and digestion were connected until I began studying nutrition, and now I'm seeing just how much of an impact it can have.

In this post I'm going to explain how healthy and normal digestion should work, how exercise can impact digestion, and then give you tips for keeping your digestion functioning well while still doing the exercise you love.

How healthy digestion should work:

  • Digestion starts in the brain. When we are in a relaxed, parasympathetic, rest-and-digest state, our stomachs begin to produce the incredibly necessary hydrochloric acid and gastric juices (including important enzymes) necessary to properly digest our food and extract nutrients from it.
  • Chewing mechanically and chemically begins to break down your food, also triggering the release of hydrochloric acid (HCl), aka stomach acid, to begin digesting properly.
  • Stomach bathes chewed food (bolus) in HCl, which helps to neutralize pathogens and to break down your food into the proper form whereby it can move on to be absorbed properly in your small intestine.
  • When the chyme (the chewed up food becomes chyme once it is bathed in acid) is acidic enough, it is allowed to pass through into the first part of the small intestine, where it is then introduced to gastric juices including enzymes, which further break down the food, and bicarbonate, which neutralizes the acidic chyme.
  • In the small intestine, the properly broken down food molecules comes into contact with the lining of the intestinal wall, where it is allowed through into the bloodstream for use as fuel for the body.
  • The remaining fibers get moved through into the large intestine, where they are fed on by the beneficial bacteria, which colonize in the large intestine. Any remaining former-food moves out of the body and is eliminated.

What is exercise?

When we think of exercise we typically think of moving our bodies in a way that increase our heart rate or makes our muscles burn for the purpose of getting stronger, faster, fitter, healthier. We all exercise for our own reasons, and I'm not here to tell you how you should be exercising. I'm not an expert in this, and I'm not pretending to be. However, there are ways in which exercise, specifically certain types, can have an impact on our digestion. I'll explain why this is important to know about from a health standpoint and also from the standpoint of helping you continue to do the type of physical activity you love to do!

What happens when we exercise?

When we do aerobic exercise/cardio we are, in a way, simulating the fight-or-flight response that we are designed to experience when we are in a dangerous situation. Think about it: our ancestors, when they had to flee a predator, would have to run to get away from it; or on the flip side, if we had to catch an animal to eat, we had to run it down. Either way, we were running, getting our heart rates up, and getting into a very specific "mode" in order to fight or flee. When we run, ride a bike, or otherwise do some sort of high-intensity aerobic activity, we switch into this same fight-or-flight response. The body doesn't know the difference between us sprinting while training for a 5k or when we're running for our lives because we are in immediate danger. So, in order to optimize being able to fight or flee from danger, as we're designed to do in limited amounts (more on this later), our body temporarily turns off what it deems to be "nonessential" functions for the purposes of surviving an immediate threat to our survival. These nonessential functions are things like reproduction, immune function, and, you guessed it, digestion.

Because these dangers/threats were usually short-lived and few-and-far between, our ancestors' bodies had ample time to recover and settle back into the parasympathetic or rest-and-digest state. But today, in our daily lives we experience pretty constant stress, from high-stress jobs, commutes, poor diet, infections, environmental pollutants, everyday life stressors (i.e. family, social/stressors), and on top of that, an inappropriate amount of exercise (either too much or too little).

Our bodies don't just respond to stress by going into fight-or-flight mode when there is an actual threat to our survival; it's all about perceived stress that our bodies are responding to. The body cannot discern from whether it's being chased by a bear to if it's running for an hour straight while training for a marathon, or if it's under prolonged chronic stress from a stressful job. As far as the body is concerned, stress is stress is stress. And if we are not giving our bodies and minds the time and space it needs to recover from these periods of intense and prolonged stress, we run into issues where the body becomes imbalanced, important enzymes and hormones become depleted, and normal body functions become compromised.

When we look at exercise, as we've discussed already, it can actually be a negative stressor if overdone without adequate recovery and/or proper support. And many of us who are health conscious actually over-do exercise even though we think we are doing the "right" thing, the "healthy" thing for our bodies. What we need to remember is that even these things that are generally considered a healthy thing can become unhealthy or damaging if done in excess.

With that said, let's talk a bit about what can go wrong with digestion if we overexercise:

We don't produce the amount of hydrochloric acid (stomach acid) we need to properly digest our proteins, neutralize pathogens, and prevent conditions like acid reflux and GERD when we are in a constant state of stress or fight-or flight.

Our stomachs are supposed to be a highly acid environment for many reasons. For one, we need HCl to properly digest our food, especially proteins, in order to break them down into their amino acid building blocks, which is necessary for them to appropriately pass through the lining of our small intestine and into our blood stream/cells to be used as fuel for all of our body's processes. The production of adequate HCl in our stomach requires certain nutrients, but it also requires us to be in a parasympathetic (rest-and-digest) state.

When we are constantly training, especially doing cardio activities like running, cycling, high-intensity interval training, etc., we are kept in sympathetic/fight-or-flight mode, and we almost never allow ourselves the time we need to get out of that state and into the relaxed, parasympathetic state. When we are constantly in fight-or-flight mode, we are not allowing our bodies to produce the HCl it needs to properly break down our food before it enters into our small intestine (begrudgingly...read on for more on this).

When our food is not broken down into the small enough molecules it needs to be to enter into the bloodstream and be uptaken by cells to be used as fuel (or for storage for later use), over time, we start to see issues with leaky gut (permeability of the lining of our intestinal tract), which can then lead to issues of chronic inflammation and other autoimmune-like responses.

Think about it: our bodies are designed to work in a very specific way (yes, with room for adaptability, but it is aiming to work in concert with other processes to maintain homeostasis). When molecules of food are larger than they should be when they enter into the small intestine (which can happen if we do not have adequate HCl and therefore do not break down our food into small enough molecules), rather than taking those food molecules into the cells to be converted into useable energy (which is what should happen), our body sees them as foreign invaders and an immune response is triggered. This can not only cause systemic inflammation, but it can also, as you might imagine, lead to us not being able to absorb/utilize the nutrients from our food, which for athletes and people who like to exercise, is critical! If we are not absorbing and utilizing nutrients from our food, we cannot use them as fuel. This can lead us to feeling tired and sluggish, not to mention inflamed, achy, unable to properly recover from workouts, and all-around feeling unhealthy.

Not to mention, our gut health suffers tremendously when we these large molecules of food are being forced through the tight junctions in the lining of our intestinal tract. Our intestinal wall is made up of cells that are very tightly connected and are designed to allow only certain/small molecules of food through. However, when the food is not properly broken down before it enters into the bloodstream, it actually sits in the intestines for longer than it should, and begins to putrefy, ferment, and go rancid, which causes irritation to the GI tract. This can lead to inflammation, pain, bloating, and gas in the intestine, which is never pleasant to deal with, let alone when we are exercising.

What else is HCl important for?

Having adequate HCl keeps us from experiencing the unpleasant acid reflux or  Gastroesophageal reflux disease (GERD) symptoms. Believe it or not, it is actually a lack of stomach acid that causes the feelings of acid reflux and GERD.

In order for food to be let through from the stomach into the beginning of the small intestine, the one-way valve (pyloric sphincter) that acts as the bouncer into the small intestine (I LOL'ed while writing that, by the way), and it will not let food pass through into the small intestine unless it is a certain pH. As we've discussed, the stomach is a very acidic environment for good reason, and if the pyloric sphincter detects that the ingested food is not acidic enough our body's innate intelligence knows that the molecules of food are not broken down enough to properly be absorbed, so they can cause problems.

So if the stomach is not acidic enough (and it has to be very acidic: .8-1.5 pH), the pyloric sphincter will not open to allow the food out of the stomach, so the food continues to build up until the two-way valve known as the cardiac sphincter or lower esophageal sphincter (which connects the esophagus to the top of the stomach) gets pushed up, and food that has been exposed to the stomach, which will have some amount of acid but not enough to be let down and into the small intestine, will feel like it's burning the esophagus. You see, the esophagus is not intended to see any amount of acid and it is a very neutral pH normally, so when food that has been in the stomach and bathed in some stomach acid and touches the inside of the esophagus, we feel a sense of burning, GERD, or acid reflux symptoms. Rather than taking acid-suppressing medications, which many people do, they should actually be looking at ways to improve their stomach acid production so that their digestion can function properly. Why don't we all just take the acid-suppressing medications anyway to address the symptoms, you may ask? Well I'll do a separate post all about that later on, but just know that it does you a significant disservice to take acid-blockers, anti-acids, etc. Feel free to email me with questions about this in the meantime!

So, long story short, without proper stomach acid, you can experience acid-reflux and GERD, but it can also cause many issues further downstream in the digestive process. Digestion is a north-to-south process, and if we are not producing enough acid at the beginning of digestion (or better yet, if our brains are not signaling our stomachs to produce enough stomach acid), we will not break down our food properly and will cause food to ferment and putrefy further down in the digestive tract, causing overgrowths of bad bacteria (or overgrowths of bacteria in the wrong places in our GI tract), leading to irritable bowel symptoms and even conditions like colitis and diverticulitis.

We inhibit the growth and flourishing of our beneficial gut bacteria.

Stress, especially prolonged and chronic stress, exercise and excessive training included, influences the ability of the beneficial bacteria, aka probiotics, to grow and flourish.

What does beneficial bacteria do for our health? Well, for one, it protects us from bad bacteria overgrowing and taking a hold. Many people think that we have good bacteria that protects us from bad bacteria, but it's actually about maintaining a balance. Because, believe it or not, we actually have what we consider "bad" bacteria in our guts all the time: E. Coli, yeast, etc. But it's when these bacteria grow out of balance that they can then begin to flourish and take over the beneficial/"good" bacteria in our guts. Because of this we need to keep the good guys growing and happy.

When we are not properly breaking down and digesting our food further upstream in our digestive system, we can actually be creating food that the "bad" bacteria like to feed on. When we do not properly chew our carbohydrates (vegetables, fruits, grains, etc.), we do not break them down adequately to be absorbed and utilized, so the remnants that make it down into the large intestine actually begin to ferment and create just the kind of food that the bad bacteria like to eat. To keep the bad bacteria at bay, we need to make sure we're creating the right environment for and balance of the good, beneficial gut bacteria, and removing the environment that the bad bacteria like to flourish in.

But don't wory! It's not all doom and gloom over here for those of us who like to exercise but who also want our digestion to be functioning optimally (who doesn't?!). Here's where I give you some tips for keeping your digestion healthy if you love to exercise.

We eat foods that we are sensitive to or allergic to.

We may not know it, but we may be regularly exposing ourselves to foods that cause inflammation because we are sensitive to them. This sensitivity of reaction may necessarily mean you are allergic to something, but it might mean that you have a compromised gut lining (as we discussed earlier), but in order to give your gut time to heal, it's important to remove the foods that might irritate your GI tract in the meantime.

The best way to do this is to keep a food journal and take note of how you feel before, during, and after your eat your meals, and notice patterns or reactions that you see surrounding certain foods. If you consistently notice that you feel gassy or bloated after eating a certain food, consider removing it from your diet for about 4 weeks and then reintroducing it. I do not recommend an elimination diet for an extended period of time. It should be used therapeutically, and is best done when working with a practitioner.

Chronic exercise can make these sensitivities worse because we are not allowing our digestion to function optimally, in the ways that we have discussed already.

What can we do to optimize digestion when we are exercising?

  • Switch yourself into parasympathetic (rest-and-digest) mode after exercising and before eating. In order to stimulate the digestive enzymes and HCl needed for proper digestion as we've talked about, we need to ensure we switch over into the rest-and-digest mode prior to eating. There are a few ways to help your body do this:
    • Take a few (5-6 at least) deep belly breaths before eating. This switches you from fight-or-flight mode into rest-and-digest mode.
    • Make sure you are seated and focused solely on your meal while eating. We need to be seated and in a relaxed state, being conscious of our meal, to truly be in a parasympathetic state.
    • Take a moment to smell your food and be grateful for the meal you're about to eat.
    • Do not drink water (or any liquids for that matter) with your meals. Drinking water dilutes the all-important stomach acid during mealtime, so it's best to steer clear of it if you can while eating. Of course, be sure to drink plenty of water, sipping throughout the day, between meals, but avoid glugging a bunch of water while you're eating.
    • Before you eat (about 15 minutes before), sip on warm or room-temperature lemon water. The acidic lemon actually stimulates the production of stomach acid.
  • Eat plenty of probiotic-rich foods
    • Fermented foods like kraut and kimchi, full-fat yogurt and kefir, and kombucha.
    • Supplement with a probiotic. Look for one with over 50 billion CFUs (look in the refrigerated section in the supplement aisle at your health food store), and look for strains like Lactobacilis, bifidobacterium, and saccharomyces boulardii.
    • Make sure to give the good bacteria/probiotics the food they like to feed on (also called pre-biotics):
      • starchy vegetables like sweet potatoes and squashes
      • cruciferous veggies like broccoli, brussels sprouts, and raw asparagus
      • underripe bananas (green bananas)
      • raw garlic and onions
  • Remove dietary stressors -- if you know certain foods upset your digestion, try removing them temporarily while you allow your gut time to recover. Then you can add them back in once the terrain (your gut) is healed.
  • Give your body adequate recovery time. If you're the kind of person who trains consistently, you might not be giving your body the time it needs to switch out of sympathetic/fight-or-flight mode, which can cause chronic low HCl production, which can take months if not years to replete. Make sure you give yourself rest days and on days when you do exercise, keep your other stressors to a minimum... which leads me to...
  • Try to minimize stressors as best you can. Remember, even though exercise can be a good thing for the body when done in moderation, it is actually a stressor when added on top of all of the other stressors we face on a daily basis. If you can make exercise fun by doing it with a friend, making sure you're giving yourself self-care days between exercise days, and generally managing your stress well, then your body will respond better and will be able to function as it should digestively even if you do make regular exercise a part of your life.
  • Consider swapping out one or two days a week of intense cardio activity with a more gentle form of movement like easy walking (my absolute favorite!), yoga and stretching, easy swimming, or very light weight training. Not only will this remove the stress of another body-stressing workout, but it your might also find that it actually works to your advantage by giving your muscles a break and shaking out lactic acid that can build up, and allowing your body to replete its stores of nutrients needed to perform at its best.

As always, please feel free to comment below with any questions you might have! In the meantime, I hope this information was helpful, and will allow you to take charge of your health while still doing the things you love.