Wednesday, March 19, 2014

Is today's gluten more toxic?

Last week I wrote how the percent gluten content of wheat hasn't changed over the course of at least the last century. In fact, you could even say wheat's gluten content has been remarkably stable in spite of breeding wheat over the years for a host of desirable attributes: improved baking characteristics, better nutrition, higher yields, and increased drought and pest resistance, to name a few. A lot about wheat has changed, and yet its gluten content hasn't.

But if the amount of gluten has remained relatively stable, could the nature of that gluten have changed over time? In particular, is the gluten in today's wheat more toxic than the gluten of old?

It's a more complex question to answer than it might appear at first glance. For example: more toxic for whom? For the sake of this blog post, I'm assuming toxic to those with active celiac disease, since that offers the richest body of peer-reviewed scientific research and published studies. For another example: when we start to explore possible answers to the toxicity question, we need to differentiate between a) ancient wheats vs. modern bread wheat, and b) changes over time within modern bread wheat alone.

I'll explore both of those angles in this blog post, discuss potential implications for the celiac/gluten-free community, and lastly, tee up a follow-up blog post about the prospect of celiac-safe wheat.

Wheat Genetics: A Brief History

When we talk about wheat, even a specific type of wheat such as modern bread wheat, we're actually talking about hundreds or thousands of actual varieties. Almost by necessity, then, we speak in generalities that overlook the variation from one wheat to the next. (That variation will become critically important in a follow-up blog post when I look at the prospect of celiac-safe strains of wheat.)

More or less all the variation in the world's wheats arises from the contributions of one, two, or three genomes—which researchers refer to as the A, B, and D genomes—each of which has 7 chromosomes. Ancient wheat varieties such as einkorn are diploid, meaning they have two sets of chromosomes from one genome (e.g., AA). Other ancient wheat varieties such as emmer as well as modern durum (pasta) wheat are tetraploid, meaning they have two sets of chromosomes from each of two genomes (e.g., AABB). Finally, modern bread wheat is hexaploid, with two sets of chromosomes from each of the three major genomes (e.g., AABBDD). (I also discuss this in chapter 1 of The Gluten-Free Edge.)

As we'll see, those three genomes—A, B, and D—code for gluten of different toxicity levels. And when more than one genome is present, they are not all expressed equally.

But by and large, the major offenders are two "families" of gluten: the alpha and gamma gliadins. They represent the real "problem children" in the gluten family. It's not all gluten that's a problem, but rather specific subsets of amino acid sequences that cause reactions in those with celiac disease. Any genome can code for alpha and gamma gliadins, but how much gliadin they cause and how toxic that gliadin is differ. Therein lies the rub when it comes to answering the "is today's gluten more toxic" question.

Ancient Wheats vs. Modern Bread Wheat

Generally, old wheats were less toxic than modern bread wheat, though all forms of wheat are generally accepted to have at least some level of toxicity for those with celiac disease, making wheat and its relatives categorically excluded from the gluten-free diet. For example, a 2006 study comparing modern bread wheat with ancient einkorn found the modern bread wheat was more toxic.

And though it's safe to generalize and say that modern bread wheat on the average has more toxic gluten than ancient wheat varieties, there is also some evidence that certain ancient varieties could have been more toxic than today's, such as a 2009 study that looked at wheat varieties such as Kamut (considered an ancient relative of modern durum pasta wheat). Not only were its gluten peptides as toxic as today's durum wheat, but it had more of that toxic gluten.

The Evolution of Modern Bread Wheat

As a hexaploid wheat, modern bread wheat contains the A, B, and D genomes. A 2012 study (and many before it, including these from 20052006, and 2009) showed that the D genome codes for the most toxic strains of gluten, followed by the A genome, and then the B. And when all three genomes are present (as they are in modern bread wheat), not all are expressed equally. In fact, the D genome—which codes for the most toxic strains of gluten—is preferentially expressed.

Further, when we look at hexaploid wheat (i.e., modern bread wheat) over time, we find that it has in fact gotten more toxic. A 2010 study, for example, compared 36 modern European hexaploid wheats against 50 hexaploid wheats grown up until about one century ago. Researchers found that alpha 9 gliadin, one of the most toxic forms of gluten, is more prevalent in the modern wheat varieties. They concluded, this "suggests modern wheat breeding practices may have led to an increased exposure to celiac disease epitopes."

Implications for the Celiac/Gluten-Free Community

As the thinking goes, for a person to develop active celiac disease, you need three things: 1) a genetic predisposition, 2) a trigger that turns the disease on, and 3) dietary exposure to celiac-toxic gluten. Much recent research has begun to look at #2, investigating possible triggers that could help to account for Americans' rising prevalence of celiac disease. The "is today's gluten more toxic" question, on the other hand, gets at #3.

It will be tempting to conclude that today's gluten is more toxic to those with celiac disease, and therefore say that today's toxic gluten is partly responsible for the rising rates of celiac disease. But that's not what the research (so far) shows. I've seen scant few studies that have examined whether the celiac-toxicity of wheat gluten is positively correlated with risk for developing celiac disease in the first place. There's an important difference between identifying those forms of gluten that are most toxic to those with active celiac disease vs. identifying the factors that cause celiac disease to "turn on" in the first place with someone with the genetic predisposition. Remember: even with today's more toxic gluten, there remain millions of Americans (and millions more internationally) who have the genetic predisposition yet still fail to develop active celiac disease despite having the genes for it.

We may very well find that the amount of gluten to which you are exposed, and—to the point of this post—the relative celiac toxicity of that gluten are risk factors for developing celiac disease in the first place. A study just came out last month in fact looking at the former. As for the latter, it for now remains a possibility but not a certainty, so let's refrain from jumping to premature conclusions, however tempting that may be to do.

In the meantime, what are we as a celiac/gluten-free community to do with this information about the relative toxicity of gluten from various modern and ancient strains of wheat? For now, not much. Regardless of their relative toxicity levels, all forms of wheat have shown at least some level of toxicity to those with celiac disease, meaning that this is a black and white issue—they're all "out" of the gluten-free diet.

For those with other forms of gluten intolerance, especially those who have some threshold of exposure to gluten to trigger a negative response, the idea of choosing less-toxic, lower-gluten forms of wheat might sound like an appealing dietary possibility. But how would you as a consumer reliably identify which wheats you should and shouldn't have?

The much more intriguing prospect is this: despite a trend in modern bread wheat toward gluten that's more toxic to celiac disease patients, researchers have been identifying individual varieties of wheat across the spectrum (modern and ancient alike) that seem to exhibit low or even no toxicity for those with celiac disease. If such varieties can be identified that still retain other desirable characteristics (e.g., yield, baking quality, drought and pest resistance), it opens the controversial door to the possibility that we might one day see celiac-safe wheat. That will be the topic of next week's post.

–Pete

2 comments:

Kalinda said...

I'm really enjoying these posts. I appreciate your level-headed approach to the topic, and I especially appreciate that you're sharing actual studies to back up your claims. I have some reading work ahead of me.

Suzanne said...

Thank you for this post! It is always interesting to read about current issues with gluten, and how it came about. This is very helpful as many friends and family members have celiac or chose the GF lifestyle. Thank you!