February 20, 2014

Digestion for (not-so) Dummies: Large Intestine, Pt.2

The large intestine. We meet again. As I mentioned last time, even though the large intestine is much shorter than the small intestine, apparently it’s still big enough to warrant more than one post. So here we are, tackling a few more issues before we’re officially done with digestion. Actually, we were pretty close to being done with digestion before we even got to the large intestine. Like I explained in the previous post, almost no further breakdown and absorption of nutrients occurs in the large intestine. Those are really the jobs of the stomach and small intestine. But there is some food breakdown here in the colon. We’ll get to that in a bit. Before we do, we’ve got some unfinished business on constipation from last week. (Get it? Unfinished business! Indeed, I’ll try to pepper part 2 of large intestine function with a little humor the way I did part 1. ‘Cuz let’s face it: poop jokes never get old. And with that in mind, lets get started with “number two on number two!”)

Okay, back to constipation. I left off last time saying we would talk about the role a backed-up bowel plays in psychological and emotional health. Regular bowel movements are pretty important. That being said, I don’t necessarily think you need to go every single day, like clockwork. (In fact, according to the National Institutes of Health, constipation means fewer than three bowel movements per week, which is obviously fewer than one a day. And if you’re going multiple times a day, most days, particularly if the urge is...well, urgent, that might be a sign you’re regularly consuming foods that don’t agree with you and your body is trying to get rid of them quickly. So going too often can be just as big a problem as not going often enough.) But if several days are passing without anything…well, passing (tee-hee), then, “Houston, we have a problem.”

Don't let your body become a landfill.
See, defecation is a normal, natural thing, and it needs to happen. When it doesn’t, bad things ensue. Think of it like a nice, clean community with regular garbage pickup. When the garbage men come when they’re supposed to and take away the trash, everything’s groovy. But let’s say the sanitation workers go on strike. So now the trash is backing up. It’s beginning to pile up in the street, and let’s say some neighborhood hooligans come by and start knocking trash cans over. The contents are spilling out, maybe some of the bags are ripping open, and now, the smelly, rotting waste that was supposed to be carted out of the neighborhood is all over the formerly clean sidewalks and lawns. This is pretty close to what happens with chronic constipation. The waste the body needs to get rid of backs up all along the colon, and some of it actually gets reabsorbed into the body. Say what?!

Yes, it sounds gross, but it’s true. Now, bear in mind, we’re not absorbing actual fecal material into the bloodstream. (Well, if we are, that is serious business and we pretty much need to be rushed to the hospital immediately before we die from sepsis.) But what we do reabsorb are bits and pieces of things that were supposed to be gotten rid of, and since the body wanted to get rid of them, there’s a good chance its because they’re harmful/toxic. We don’t necessarily get sick when we reabsorb wastes, but we can certainly feel less than our best.

Here’s how it works: the large intestine is full of colonic bacteria. Most of these are good guys, and they’re supposed to be there. When I mentioned at the beginning of this post that a little bit of food/nutrient breakdown occurs in the colon, this is what I was talking about. These beneficial bacteria feast on some of the undigested particles that come through. Most often, they feed on carbohydrates—sugars and starches, such as the undigested lactose in lactose-intolerant people. They also feed on what is known as “resistant starch” – starch from things like white potatoes that resists full digestive breakdown until it gets to the colon. (There’s a ton of talk about RS in the Paleo world these days. You can do a search if you’re so inclined. This resistant starch is an example of the prebiotics I mentioned in a past post, when I said prebiotics serve as food for probiotics.) So these bacteria can help us out by breaking down some of the things we can’t. (This is true in ruminant animals, too. Sometimes they have trouble breaking down cellulose, too, but the enormous chambers of their digestive systems are basically “fermentation tanks” that are loaded with bacteria that can dispatch cellulose. This is how cows, sheep, goats, and other ruminant herbivores literally turn grass into protein.)

Good bugs!
We are absolutely loaded with these bacteria. In fact, we have more bacterial cells inside us than human cells. (I once heard someone say we should be called “Homo bacteriosapiens.”) So we’re talking trillions. This is why when we take probiotics, they’re typically in the billions range of colony forming units (CFUs). And since that’s still just a small percentage of the total inside us, bottled probiotics have to have multiple billions of CFUs, because some will inevitably lost to stomach acid and digestive enzymes. So if we take very high amounts, we increase the likelihood that some of them will remain intact and reach their target destination (the large intestine) and populate.

These bacteria don’t just break down the tough, fibrous plant matter we have a hard time with, like kale stems, broccoli, and stuff like that. In the process, they actually produce some vitamins and good fats (like K1 and some of the B vitamins, plus short chain fatty acids, like butyrate, the predominant fatty acid in butter). However, we’re not sure to what extent we absorb and benefit from those nutrients, versus the bacteria themselves using them. It seems that we do absorb some of them, but nowhere near enough to meet our daily needs for optimal health. (Seems more like a failsafe to me—a last-ditch effort to squeeze some nutrients out of whatever the bacteria can latch onto when we’re either not consuming enough total food, or not consuming the right things.) Something else these beneficial bacteria produce is gas. They generally feed on these resistant starches and other not-fully-digested carbohydrates by fermenting them inside the large intestine, and the end result is gas. This is why some people experience a lot of flatulence when consuming certain foods--typically beans, but also cruciferous vegetables and fibrous greens. (There are ways to prepare beans that can reduce the gas-producing effects, usually by a long soaking and fermentation process that kind of pre-digests some of the starches that are difficult for us to break down. Check out info on a chart my friend Monica created with guidance on how to soak beans and grains for optimal digestion and nutrient absorption.)

Aaaanyway, back on track. We need these gut good guys. This is why it’s so important to repopulate your GI tract with pre- and probiotics after a course of antibiotics. Think of it like hiring new sanitation workers to come take the trash out.

And speaking of taking the trash out, let’s go back to that analogy where the garbage is spilling out all over the nice, pretty neighborhood. In addition to all the good things these colonic bacteria do for us, they can get us into trouble as well. (Well, there are good and “bad” bacteria in the colon, so maybe it’s just the bad ones that mess us up, but either way, it’s colonic flora that does it.) The way they mess us up is by secreting enzymes that are akin to the garbage-spilling hooligans I mentioned earlier. When the liver tags toxins and waste products for removal from the body, it does so by connecting them to other substances that escort them out (called conjugation in biochem speak). The crazy party trick these bacterial enzymes have mastered is deconjugating the wastes. That is, when feces sit in the colon for a while without being moved out, the bacteria break the connection between the toxins and the escort molecules, which allows the body to reabsorb them. Eek! The stuff that was supposed to go out is now coming back in.

Let’s think about what could result from this scenario: how about depression? How about anxiety? How about any mood alteration that could be brought about by having wastes circulating in the blood? And let’s not forget about the physical effects, either. Constipation is just plain awful, particularly when it’s chronic. If you get a little stuffed up once in a while, it’s not that big a deal. It probably has more to do with your brain than your body anyway. But when you spend months (or years!) going just once or twice a week—or sometimes not even that often—it can be downright debilitating. When things are really backed up, you feel full, heavy, and sluggish, for obvious reasons. You’re not exactly bursting with energy, and going for a nice walk outside in the fresh air is probably the last thing you feel like doing. (And hitting the gym for an honest workout couldn’t be further from your radar.) And aside from the physical effects of the toxins getting reabsorbed, there’s the obvious connection between feeling stopped up, heavy, and full, and being depressed. If you haven’t had a good, easy, complete BM in a week—or two or three!—there’s no way you’ll be upbeat, happy-go-lucky, or feel any other lighthearted, positive state of mind. This is what I meant when I said the colon was large and in charge—in charge of moods.

Here’s a real-world example of how constipation and bacterial deconjugation can cause and/or exacerbate a health situation. (Yours truly may or may not have some unfortunate firsthand experience with this.) The condition known as estrogen dominance is becoming more common among women in the industrialized world. There are many reasons for this, but the bottom line is, we end up with too much estrogen. Estrogen is, of course, a normal, natural, and mostly good thing. But we can definitely get too much of a good thing. When I keep saying that the liver and large intestine are trying to get rid of “toxins” and “wastes,” the “wastes” part of that includes byproducts of normal physiological processes and metabolism—for example, excess estrogen. (Some of the “excess” comes from xenoestrogens in plastics and cosmetics, but I’m also talking about when our own bodies produce too much, which can happen for many reasons.) So the liver conjugates the excess estrogen and sends it through the lower GI tract to exit the body. But when we’re chronically constipated, the wastes sit unmoving in the colon, giving the bacteria ample time to deconjugate it, allowing the body to reabsorb the estrogen. Oy vey! And keep in mind, this is only one example. This deconjugation action can happen with other hormones, plus plenty of other compounds, both natural to the body and completely foreign. (Note: thanks to a naturopathic doctor who knew what she was doing [and a little self-help from yours truly who also knows a thing or two about this], I am faring much better these days. Woohoo!)

Whew! That was kind of a long discussion, but I hope it helped things make sense. We’ve got a couple more things to talk about before we’re done.

What if you are chronically constipated? I’ve said that drugstore laxatives and stool softeners are a short-term fix for a long-term problem. But that doesn’t mean we should avoid them entirely. Ultimately, we want to work with a qualified professional to uncover the root cause of bowel dysfunction, but that could take a while. (And even when it is identified, it could take an even longer while to correct it.) And in the meantime, for all the reasons we talked about today, we’ve got to get things moving. It’s okay to use these short-term fixes to help us deal with the acute situation as long as we’re also working to resolve the chronic issue. I think Ex-Lax and things like that are all right, but I much prefer laxative teas. I like Yogi brand’s Get Regular®, and Traditional Medicinals’ Smooth Move®. You can also loosen the ol bowels a bit by taking a high dose of magnesium, such as with Natural Calm.

Another godsend for the chronically “backed up” is colon hydrotherapy, also known as a colonic. Colonics are like enemas on steroids. (Or should I say enemas on crack? I did promise you some colon double entendre.) They’re not for everybody, but yours truly may or may not be able to tell you from firsthand experience that when you seriously haven’t gone in ages, a colonic will literally clean you out and let your large intestine sort of reset and start from scratch. Truly, I don’t subscribe to many of the more woo-woo energetic type healing modalities, but I can tell you the occasional colonic isn’t just for spoiled, raw vegan starlets who think they constantly need to “detox” from the ravages of everyday life. (Or perhaps their raging cocaine and alcohol habits.)

Last time, I said good nutritionists love to talk about poop. Since I place myself in this category, let’s talk about it! I’ve recommended Diane Sanfilippo’s book, Practical Paleo several times in previous posts. There are a ton of reasons why it’s a wonderful resource (check out my review on Amazon), but she has a “Poop Pageant” in there that is pure gold. (She modeled it after the one in How to Eat, Move, and Be Healthy, by Paul Chek.) It sounds just like what it is: an illustration (no actual photographs, thank goodness!) of the most common different types of “poo,” and what they reveal about what’s going on in your digestive tract. Too stiff and hard? Too runny? Weird color? (Either black and tarry or maybe kind of clay colored?) Bits of undigested food peeking out? These are all signs of less than optimal digestive function. I’ve said it before, and I’ll say it again: Don’t just drop off the kids and run. Look at your poop! (You don’t have to talk about it at the dinner table, but when you’re having a moment to yourself in the privacy of your bathroom, do make a point to observe.)

What else? Well, there’s always irritable bowel syndrome, which comes in two fun flavors: IBS-C (for constipation) and IBS-D (for diarrhea). We’ve covered enough for today, though. I’ll just say this about IBS: it is often caused by a food intolerance, most commonly gluten. (Surprise, surprise.) And its exacerbated by stress. If you search the testimonials of Robb Wolf’s or Mark Sisson’s sites, or the Wheat Belly Facebook page, you will find countless success stories from people who have stopped and/or put into remission their IBS & IBD with nothing more than a change in diet. (Same goes for colitis and Crohn's disease. In fact, if youre familiar with Robb Wolfs history and how he, himself, stumbled upon Paleo, you know he was about 10 seconds away from a bowel resection and damn near deaths door because of some seriously terrible intestinal juju. He discovered the work of Loren Cordain and Boyd Eaton, ditched the foods that were irritating the bejeezus out of his GI tract and causing major malnutrition, and the rest is history.) It makes perfect sense that if something we eat really doesn’t agree with us, the GI tract will rebel.

There’s also diverticulosis and diverticulitis. I don’t know much about these, so I won’t comment. I’ll simply point you to the experts, and tell you that, according to them, a low fiber diet is not likely the cause. I can tell you, however, that the conventionally parroted ban on nuts for people with diverticulosis/itis is a thing of the past. Why would nuts get stuck in those pouches but nothing else? And those nuts should be chewed anyway. If you were swallowing whole, intact peanuts or cashews, maybe I could see them getting stuck, but if they’re well chewed, they’re essentially no different from any other type of food that goes down the hatch.   

And that’s it for the large intestine, folks! In fact, that’s it for all of digestion.

We’ve covered the whole process, from ingesting food all the way down to expelling the remains of that food. If I may be so bold as to quote a masterpiece of American cinematic achievement and quite possibly one of the greatest movies of all time (or, at the very least, the late 1980s), we’ve “gone from suck to blow!

Do you have any questions about anything we’ve covered? Did I skip something you were hoping I would address? Let me know in the comments. I’m happy to take requests.  ;-)

P.S. One bit of gee-whiz info about those trillions of colonic bacteria: they make up the majority of our poop! Our solid waste material is the remnants of the food we eat, the biological wastes, and loads and loads of those bacteria! They die out and get replaced very quickly, and all the dead ones take the same egress route as all the other wastes.

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. Another fine installment of a great series.

  2. Do you have any insights into colonic parasites? Pin worm in particular. It has a high prevalence rate, is it commensal, pathological, or beneficial?

    1. I'm not sure. Worms & parasites definitely aren't my area of expertise. I'm pretty sure pinworms are pathological, but I'm not sure. Sorry...