December 18, 2013

Digestion for (not-so) Dummies: Small Intestine Pt.2 - Leaky Gut

Hey Everyone! We’re in the home stretch now! It’s taken us a while in this series on digestion, but here we are, covering a few more key things about the small intestine, then it’s on to the large intestine, and we’ll be done! In previous entries, we’ve done some troubleshooting to help digestion in the stomach, the pancreas, and the gallbladder. Today, let’s get into one of the most common—but least recognized by conventional medical and nutrition professionals—consequences from poor digestion: Leaky gut!

We’re still waiting patiently at the small intestine station along our long train journey north to south through the digestive tract, from the brain to the bottom. You’ll recall that last time, I explained a little about the anatomy of our small intestine, and how it’s kind of like a shag carpet. At the risk of mixing similes and metaphors here, it’ll be useful if I introduce another analogy to help us picture our small intestines and really understand what’s going on in there. Besides the shag carpet deal, a great way to think of the SI is like a screen on a door or window. Window screens are basically sheets of extremely thin, soft metal (or fabric) that have tiny holes in them, right? Those holes have two primary purposes: to let good things in (like fresh air and the smell of brownies baking), and to keep bad things out (like mosquitoes and flies). In order to succeed at these tasks, those holes have to be a certain size. Too small and the good stuff won’t pass through; too big, and the bad stuff will. The lining of the small intestine is the same way.

If we think of the small intestine like a screen, what would happen if something came along and punched a bunch of big holes in that screen? Exactly what we just mentioned: bad things that are not supposed to get through will come in in droves. This is bad enough when we’re talking about actual screens and the result is an insect infestation in your house. But what about unexpected and potentially dangerous things getting into your bloodstream? If you think that sounds like a recipe for disaster, pat yourself on the back because you are correct!

Holes: great for golf courses; terrible for our small intestine!

Warning: I have to get a little scientific for a sec. I promise, it won’t hurt and it’ll be over quickly. (Plus, I bet I’m a lot cuter than your high school biology teacher.) So, leaky gut. How do our guts become leaky, and what are the consequences?

The cells that line our small intestine like each other. A lot. They like each other so much, in fact, that they stick together very closely. The way they do this is through something called tight junctions. (There are lots of ways cells stay together. Tight junctions are only one example. Check out illustrations here and here.) Tight junctions are just what they sound like: they keep cells together tightly and don’t allow anything to pass in between. (Or only teeny tiny things that are supposed to squeeze through.) The thing is, there are lots of things that can mess with these tight junctions and cause them to become…well…not so tight. These agents act upon the tight junctions and loosen them up, which opens a little space between the cells. So now, where there used to be a barrier, there’s a space through which things can pass that are not ordinarily supposed to pass through. The “screen” that lines your small intestine has just gotten a bunch of holes punched in it and now you’ve got a leaky gut. (The science-speak term for this is “increased intestinal permeability.” Makes sense…after all, the permeability of your intestine has increased. Whoot!)

If we’ve learned anything so far from this series on digestion, it should be that the GI tract is designed very beautifully. Even though it is one, continuous, hollow tube from the mouth all the way down to the booty, the shape and makeup of this tube change as we go from north to south. Each part is built to perform a specific function. The small intestine is built to absorb molecules that make up food: amino acids & small peptides (from protein), monoglycerides and free fatty acids (from fats), and simple sugars (mono- and disaccharides from carbohydrates). For the most part, only molecules this small can be transported into the cells that line the intestine, where they’re modified a bit and then sent into the bloodstream. (Think of those cells like teeny, tiny processing plants.) When the gut is leaky, however—and there are bigger spaces in between the cells—bigger molecules bypass this step and instead of being brought into those individual cells for final processing, they sneak through those spaces and enter the bloodstream directly. (For an out-freaking-standing illustration of this, check out this one on the Balanced Bites website.) If this doesn’t sound like that big a deal, hang onto your hat. We’re about to put the pieces together.

Do you or anyone you know have an autoimmune condition? This is where our immune systems get confused, go on overdrive, and start attacking our own tissue. Among many other conditions, this can cause:

Rheumatoid arthritis
Hashimoto’s thyroiditis
Multiple sclerosis
Grave’s disease
Type 1 diabetes
Sjögren’s syndrome
Ankylosing spondylitis
Do you know how these things happen? Why is it that our own immune systems would turn against us? It all comes back to the leaky gut concept. Here’s how it works:

Let’s say one of the bigger molecules I mentioned earlier has slipped through the spaces and entered the bloodstream. Most likely, this bigger molecule is a peptide—a few amino acids strung together. For the sake of an example, let’s say this peptide is made up of the amino acids alanine-serine-proline-tyrosine. A-S-P-T. That’s a pattern. The immune system—doing what it is designed to do and exactly what it is supposed to do—sees this unexpected peptide in the bloodstream and mounts a defense against it. Okay, no problem. Crisis averted.


What happens if that pattern—the A-S-P-T in our example—happens to also appear on proteins that make up, say, the insulin-producing beta cells of your pancreas? Now that the immune system has been trained to seek and destroy that pesky A-S-P-T pattern, it might seek and destroy it in places that are completely benign, like our own healthy organs, glands, and other tissue. With the beta cell example, if your immune system destroys enough of those, you end up with type 1 diabetes. If your immune system has been trained to seek and destroy a pattern that happens to match one on a protein that’s part of the myelin sheath that insulates your nerve cells, you end up with multiple sclerosis. Your thyroid gland? Hashimoto’s or Grave’s. Your joints? Rheumatoid arthritis. But the key thing to understand here is, all of these autoimmune conditions stem from the same underlying cause: a leaky gut.

There’s a pretty cool illustration of this here. If you are especially science-minded and want to “geek out” on the research, I recommend searching for the work of Dr. Alessio Fasano. (There’s also a fantastic podcast interview with him here. [Available free on iTunes as well.])

Rheumatoid arthritis. What’s really the problem here?
Is it the hands, or the GUT?

At this point, the next obvious question is: what makes our gut leaky? What are the things that come along and punch those nasty holes in our gut?

There are a lot of things. In fact, my guess is that scientists haven’t yet identified everything that messes with those tight junctions. I’ll address just three of them here. The first one is stress. Yes, it’s true: being chronically stressed out can cause a leaky gut. To be honest with you, I’m not sure of the biochemical mechanism at work here. All I know is, since stress dumps water all over our digestive fire from the get-go, it’s just bad news all around. My educated guess is that leaky gut is a byproduct of the compromised digestion that results from stress. If you’re stressed out long-term, you’re not breaking down and absorbing nutrients well—and these nutrients are needed for proper functioning of everything, including the proteins that make those tight junctions. A vicious cycle if ever there was one. It could also be a direct effect of cortisol. According to Chris Kresser, “Experimental studies have shown that psychological stress slows normal small intestinal transit time, encourages overgrowth of bacteria, and even compromises the intestinal barrier.” (Hint: “compromised intestinal barrier” is yet another fancy way to say leaky gut.)

Other things that interfere with the proper functioning of the gut lining are pharmaceutical drugs. This includes very common drugs, like NSAIDs (aspirin, acetaminophen, and ibuprofen) and antacids. It also includes steroid drugs, which is ironic, because steroids are often frontline therapy for autoimmune conditions. (Steroid drugs suppress the immune system, which reduces the pain and inflammation associated with certain autoimmune issues. Interesting that they can also induce and worsen the leaky gut that is likely causing the condition in the first place, no?) Is one dose of aspirin going to give you Grave’s disease? No. Not any more than stressing out over a big deadline at work once in a while is likely to bring about lupus. But there are people—and we all know some—who take these drugs or live under high stress levels every day, for years. It’s this chronic, long-term stuff that might be problematic.

Other factors that can lead to leaky gut are things like alcohol, antibiotics, and infections. But the third major player I want to mention here is gluten. It’s far too big an issue to get into now, though. It really deserves its own post. So if you think gluten sensitivity and gluten-free diets are nothing but faddish nonsense, hold on until next time. We’ll talk about why this protein—found in wheat, rye, barley, and a few other cereal grains—is more problematic than you might realize, and why I wish I had come up with the brilliant phrase, “amber waves of pain.”

In the meantime, for an insanely awesome explanation of all this, check out more brilliant work by Diane Sanfilippo: Is Your Gut Leaky?

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.

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