September 26, 2013

Digestion for (not-so) Dummies: The Brain

Welcome back to Digestion for (not-so) Dummies. In the intro to this series, I explained that digestion is a north-to-south process, and that this process starts even before we reach our actual gastrointestinal (GI) tract. In fact, it starts about as far north as you can get: the brain. (Or the head, if you prefer, which, as Tom Hanks’s character, Jimmy Dugan, points out in quite possibly one of the greatest movies of all time, “That’s that lump that’s three feet above your *ss!

In order to get the entire digestive train out of the station on time and moving steadily toward its first stop, the brain’s got to do its thing. And it’s got to do this thing before we even take our first bite of food. If it doesn’t, the train’s just going to sit there, all the poor suckers on board are going to miss their connections, and other trains coming up behind are going to be held up. Havoc will be wreaked overall. So, what is the brain’s thing? Read on…

Digestion is inarguably a physiological process. But it’s also inarguably a state of mind. Namely, the parasympathetic state. You’ve heard of the fight-or-flight mechanism, right? Well, that’s the sympathetic part of the nervous system at work—the one that gets riled up, excited, angry, worried, stressed out, or otherwise suited to…well, fight or flee. But the parasympathetic nervous system is responsible for the rest and digest side of things. This is big. Very big. 

Aaaah! Don’t worry about digesting 
that burrito—just get me 
the heck out of here!!
Here’s the deal: when you are in fight-or-flight mode (sympathetic dominant), you will not digest your food well. Period. End of story. Do not pass GO, do not collect $200. From a physiological standpoint, this makes perfect sense. Looking through an evolutionary and biological lens, when would you feel apprehensive, nervous, scared, angry, or stressed out? When there’s some kind of danger around, right? Like, say, you’re all alone out on the prehistoric savannah, a tiger is about to make you its dinner, and you’ve got no Range Rover to jump into and speed away. You’re toast unless you stay and fight, or run for your life. At this point, digesting food is your body’s last priority. Its main focus is keeping you alive. So, instead of wasting precious energy producing stomach acid, digestive enzymes, and the muscular contractions that help propel food along your GI tract (geek-speak for this is “peristalsis”), it’s going to marshal all its resources toward things that will help you in this life-or-death situation: speeding up your heart rate and raising your blood pressure so your muscles get more oxygen more quickly; and stopping or slowing down all functions that are unrelated to making you run faster or fight harder (such as reproduction, repair, digestion, getting sick, and, in some cases, elimination…i.e. going the bathroom. More on that in the post about the large intestine.)

Since it’s been a while since any of us were caught unawares out on the savannah, how does this translate to modern life? Glad you asked! See, millions of years of evolution while we were vulnerable to some pretty gnarly predator/prey scenarios have honed our brains to perceive benign everyday stressors as life-or-death deals. You know what I’m talking about — don’t you sometimes get very aggravated behind the wheel in rush hour traffic? Or feel your blood start to boil if you happen to catch a clip of political talk radio and they’re mercilessly badmouthing “your guy?” (Or gal.) Maybe you feel your heart start racing and your breath coming faster when there’s a difficult deadline looming at work, or the guy over in the next cube is clipping his nails at his desk. (What? You mean you don’t have gross coworkers like I do who do their personal grooming in the office? Lucky you.)


So yeah, we’re surrounded by situations every day that, in the grand scheme of things, are no big deal, but letting them get to us is a surefire way to get ourselves into sympathetic mode and cut good digestion off at the knees. Of course, some people handle stress better than others. It’s not so much the situations themselves, but how we react to them. I, personally, have serious road rage. I also get inordinately furious when my neighbors let their very loud dogs into their backyard at 7am on a Sunday and let them proceed to bark for half the afternoon. (The same goes for people who start lawnmowers at the crack of dawn on weekends. Seriously, people? Seriously?! If this is what passes for common courtesy around here, I’m moving to Mars.) But other people might take those things in stride…put on some good music and stay calm despite the bumper-to-bumper traffic, pop in some earplugs and ignore the dogs, etc. 

Aaaaanyway, to sum up: Our digestive process is put on hold when we’re worked up about something.

So how do things go when we’re not angry, worried, or stressed out? This is the nice, happy time when we’re relaxed, calm, and parasympathetic dominant. Good things happen when our body does not sense that we need to run away from a wild animal. If you’re a fan of cooking shows (and who isn’t), you’ve probably heard many professional chefs say that you first eat with your eyes. This is why presentation—the way food looks—is so important. The way food smells is also important. Why? These sensations suggest to our brain that we’re probably going to eat soon. Knowing this, the brain signals the salivary glands to start secreting saliva. (This is why you sometimes start drooling at the smell of bacon, or even the mere thought of bacon. OT: I love my veggies as much as anyone else, but I challenge anyone to tell me honestly that they drool at the sight of a raw kale salad.) It also gets the stomach ready to start secreting hydrochloric acid (HCl), otherwise known as stomach acid. Note that these are preparatory things that happen before we’ve even taken a bite of anything. So you can see why it’s important to calm down for a little while before eating.

This looks like a good time to eat. 

How can you calm down? Well, if you’re not feeling especially stressed, there’s nothing to worry about. You’re already there, in parasympathetic mode. But if you’re at work and you’re the cube-dwelling type, I urge you to step away from your desk and eat at an actual table like the highly evolved Homo sapiens you are. No shoveling food in, hunched over your computer like a feral animal. Our digestive systems deserve better than that from us. Eating in a pleasant environment is important. If there’s truly nowhere for you to “escape” to for enjoying your meal in a civilized manner, stay at your desk, but for goodness’ sake, don’t work. Don’t pick up the phone, don’t reply to emails. Just. Eat. You might be a champion multi-tasker, but your digestive system isn’t

Not a good time to have lunch.

Something else that can help is saying grace, giving thanks, or otherwise just sitting quietly for a few minutes to calm down and take a few nice, slow, deep breaths. Whether you believe in a higher power or not, there’s nothing wrong with taking a minute to express gratitude for the food before you, even if you’re just thanking yourself for cooking or buying it. (No, really. Good for you!) The point is, be calm before you eat. (And for the love of all that’s holy, SIT DOWN! Please, please, do not eat standing up. Can you imagine the signal that sends to your brain? You’re literally poised to fight or flee! Oy vey!)

The second key thing when it comes to the brain is to slow down. I’ll cover this in more detail next time when we talk about the mouth’s role in all this, but as for the brain, if you eat too quickly, food will reach your stomach before your brain’s even had the chance to send the signals I mentioned earlier. Jump the gun much? That would be like the train departing the station early, which can wreak just as much havoc as it leaving late. Throughout our digestive process, from top to bottom, things are supposed to happen in certain places at certain times. When they don’t, cars start derailing, nuts & bolts pop off the track, and mayhem ensues. (Do I have to remind you of that classic clip from I Love Lucy, where Lucy and Ethel work in the chocolate factory? It’s easy to see what happens when things come at us before we’re ready. Whether it’s a candy assembly line or your GI tract, the results ain’t pretty.)

In our overly fast, overly stressed, overly angry, and under-sleeping, under-joyed, and under-peaceful modern lives, we’ve lost sight of the simple pleasure of a meal. Yes, of course, it’s easier to appreciate this when we’re surrounded by good friends and loved ones, and there’s nourishing, whole, home-cooked food on the table (and a bottle of wine or two making the rounds doesn’t hurt), but it’s perfectly possible to enjoy a meal alone, too. No white tablecloth or candlelight required; just a calm, quiet pocket of time, real food, and the grace of allowing your body to do what it does best.

So that’s it for now. Just calm down, eat slowly, and enjoy. Trust me: your GI tract will thank you for it.

Intestinal bliss: so fabulous, yet so fragile.


Remember: Amy Berger, M.S., NTP, is not a physician and Tuit Nutrition, LLC, is not a medical practice. The information contained on this site is not intended to diagnose, treat, cure, or prevent any medical condition.


  1. I love this blog post! I had a stress related episode today while eating lunch and my body totally freaked out. I actually blogged about my experience and I when I Googled digestion starts in the brain, I found this page! Great info that you are sharing.

  2. Thanks, Jennifer! Sorry you had a bad time with your "last lunch," but I guess you learned firsthand about how all this works. And I agree with you -- even when we eat things that are "off-plan," or "cheat," or whatever you want to call it, if we do it with intention, with love for ourselves, and with the mindset to *enjoy* it and move on, I don't think it has the negative effects it would if we worried and berated ourselves. Your blog looks great!

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