Why is gluten so hard to digest? What's the relationship between gluten intolerance and sourdough? Is sourdough gluten-free?
Along with “Why am I always cleaning the stove?!”, these questions have been stewing on my back burner for several months (hehe, see what I did there?). 😉
They are near and dear to my heart. I was sensitive to gluten. As a kid, it meant laying flat on my back with a crippling stomach ache instead of swimming in my grandma's pool. It meant missing out on every. single. birthday cake, and subsisting on buckwheat pancakes that never really appealed to my 10-year-old heart. (Sorry, mom!)
Thankfully, all those buckwheat pancakes were good for me, and so was the gradual introduction of soaking, sprouting, and sourdough methods. My gluten intolerance is now a thing of the past.
And as I've grown up, I've realized that conventional birthday cake isn't all it's cracked up to be. A gluten-free, grain-free lifestyle can be awesome. And a mom who puts buckwheat pancakes on the table deserves all the kudos in the world. 😉
Yet the questions remain: Why is gluten itself often harmful? Does sourdough make it more easily digestible? If so, how?
First, Let's Define Some Terms
The smallest unit of a protein is called an amino acid.
When any 2 amino acids bond together, they form a dipeptide.
Tripeptides are any 3 amino acids bonded together.
An oligopeptide is a small number of amino acids (but still more than 3) bonded together.
Finally, a protein is at least 1 long chain of amino acids.
In grains, the gluten proteins are divided into 2 categories: the glutelins and the prolamins (source).
In wheat, the glutelin and prolamin proteins are called glutenin and gliadin, respectively (source). Although glutenin may contribute, gliadin is widely recognized as the main cause of gluten intolerance (source and source). It is these 2 gluten proteins — present in varieties of wheat — that I will focus on in this post.
The Players: Glutenin and Gliadin
Glutenin and gliadin form a protein network responsible for many of the characteristics of dough, such as its plasticity and elasticity (source). It molds easily under pressure and tends to revert back to its original shape once pressure is released. This allows it to expand to incorporate gases during breadmaking, but also resist just enough that these bubbles don't pop!
Glutenin proteins are twisted and coiled into long chains. Dough elasticity comes from the ability of these springy coils to store energy when stretched. This energy is later released as the dough resumes its original shape. Dough elasticity weakens over time. (On Food and Cooking, page 523.)
Gliadin proteins are dense and globular with a low surface area-to-volume ratio. This means that they allow glutenin chains to slide freely past in the protein network, contributing to the plasticity of dough. Additionally, they have high concentrations of the amino acids proline (about 1 proline in every 7 amino acids) and glutamine (source).
The proportions of these proteins in different types of wheat (einkorn, emmer, spelt, kamut, etc.) determine the relative strength of each dough.
Other factors affect dough strength, too, such as the water, salt, and sugar content, any fats present, the dough's acidity, and how long the dough has been kneaded. (On Food and Cooking, page 523.)
Digestion of Wheat Gluten
Glutenin and gliadin are digested in the stomach and small intestine by enzymes (source).
In glutenin's case, enzymes cleave its long chains into oligopeptides, then into tripeptides, dipeptides, and free amino acids (source). It is these latter 3 that absorb into the body and go on their merry way.
Now enter gliadin. In sensitive individuals, gliadin is broken down into oligopeptides but no further (source). This is due to its low surface area and specific amino acid sequences that inhibit enzymatic activity (source).
As it turns out, proline's cyclic structure contorts gliadin enough that special enzymes are required to degrade it (source) .
The enzyme tissue transglutaminase (tTG) plays a role, too. It creates bonds not only between separate gliadin proteins, but between distant amino acids in a single gliadin protein as well. This makes them even harder to digest. Picture a dense, tangled web that just got more tangled! (Source.)
tTG also changes glutamine into glutamic acid via a process called deamidation. This increases the likelihood of an autoimmune response — where the body not only targets the modified gliadin, but also tTG itself. (Source, source, and source.) This results in inflammation.
And so, these gliadin oligopeptides — resistant to further enzymatic degradation — may damage the gut by blunting villi and increasing permeability (source and source). This can lead to celiac disease, nutrient malabsorption, and more (source).
Is Sourdough Gluten-Free?
I was 13 when I first tried my hand at my very own sourdough starter. I whipped up flour and water and tried not to check on it too often. It sprang to life as obligingly as I could wish. I even documented its progress with a twice daily photo shoot.
I didn't ask the question then, but I ask it now: what does sourdough do? Is sourdough gluten-free? Does it actually solve the problem of toxic, mayhem-causing gliadin fragments in our gut?
Let's talk about lactic acid bacteria (LAB) — present in sourdough. As LAB convert the sugars in wheat flour to lactic acid, the acidity increases. This facilitates hydrolysis of gliadin proteins by penetrating and loosening the gluten network. It also activates enzymes present in wheat flour itself — enzymes that work optimally in acidic conditions. (Source.)
Then, as discussed in this study, notable strains of LAB hydrolyze wheat proteins (including gliadin, and the non-gluten proteins albumin and globulin) by factors greater than 50% over a 24-hour period.
This means that the bacteria and their associated enzymes are effectively cleaving gliadin proteins before they ever reach the gut. This is supported by rising levels of free proline as it is released from degraded proteins. As we already know, gliadin is rich in proline.
And while we're on the subject of LAB…
“[S]ourdough cannot be used as the only component of the baking dough in the traditional technology; nevertheless, this study is the first to show that selected sourdough lactic acid bacteria have hydrolyzing activities towards prolamin peptides involved in human cereal intolerance. These activities could be easily improved under more suitable technological conditions and/or addressed to the production of special sourdough-type breads with low contents of gliadin toxic peptides.” (Source.)
So, is sourdough gluten-free? No.
It does, however, make gliadin proteins easier to digest.
Are there any other benefits to sourdough?
In addition to lessening bread's affect on blood sugar, sourdough also provides an increase in available minerals by reducing phytic acid (source). It also delays staling and resists spoilage microbes (On Food and Cooking, page 544).
Is It Possible To Heal Gluten Intolerance?
Why am I able to eat gluten today — in any form, sourdough or not? Perhaps it is because the damage to my gut was reversible. After eliminating gluten, it needed only the time and resources to heal.
After a while, I gradually reintroduced gluten in its less toxic, sourdough form.
Now, I maintain my gut health by continuing sourdough and other preparation methods — and eating only the very, very occasional birthday cake. 😉
To be sure, sourdough may not cure any gluten allergies, whether celiac disease or some other form of gluten intolerance. It doesn't even completely eliminate the gluten content.
It is, however, a fascinating preparation method — bubbling away on countertops all over the world! — and it affects the toxicity of gliadin in a very real way. For some, it may even provide a means to eat bread again.
Do you have, or have you had, any type of gluten intolerance? Has sourdough enabled you to eat gluten? Do you want to try it? Share your experience in the comments below!
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