Many people who undertake the Paleo Diet often experience problems when introducing gluten back in to their diet despite not having noticed any issues prior to beginning the diet. There could be a host of reasons for this phenomenon. First, they may have had an issue before and never noticed. Many people see relief from multiple issues when beginning a Paleo Diet, perhaps gluten was the issue. Secondly, there could be a change to the microbiome that occurs with the diet. In this blog we will explore a few studies that could be evidence for this second reason.
While humans are unable to fully digest gluten because they lack the enzymes to do so, there are many strains of bacteria that colonize the GI tract that can. A recent study that looked at the microbiome of 22 human subjects found that 144 strains of bacteria found in the feces may participate in gluten metabolism(1). Some of the strains were able to metabolize gluten themselves while others made enzymes that could degrade gluten extracellularly, perhaps to break up the peptides for other symbionts.
The interesting part of this study is that a few of the strains were able to break down one of the more problematic peptides for people with celiac disease, the 33-mer. Obviously the more gluten you consume the more abundant these species would become holding everything else constant, so losing a few of these guys could be an issue. Going from a diet high in gluten to one very low in gluten and then testing the waters with a weekend gluten bomb may overwhelm your bugs' ability to breakdown gluten and, voila, problems.
Another study in 2010 found that microbes found within dental plaque and saliva produced enzymes that are capable of degrading gluten in vitro(2). These enzymes were capable of degrading 2 of the more problematic proteins found in gluten, the 33- and 26-mer. Interestingly, these bacteria can do so over a wide pH range meaning they could, in theory, work in regions of the digestive tract outside of the mouth. Even more interesting is that people who undertake a Paleo Diet tend to see an improvement in oral health which includes improvement in plaque deposits in the mouth. Could this lead to a decreased ability to metabolize gluten due to a drop in abundance of these gluten degrading microbes?
A follow up study by the same authors zeroed in on a couple of specific strains of microbes with powerful gluten degrading capabilities. These microbes had a powerful ability to break down both the 33- and 26-mer peptides with the remaining proteins not being able to initiate an immune response(3). One of these microbes was found to colonize both the oral cavity as well as the duodenum, meaning it may participate in gluten degradation in both the mouth and small intestine. While healthy subjects did have a higher percentage of this bacteria in the duodenum than people with celiac disease, the difference was not significant(6.5% vs 5.9%).
Looking at these studies, we can come to some conclusions. First off, while humans cannot digest gluten, there are microbes in the upper part of the human digestive tract that can. Second, there is the potential that initiating a gluten free diet for an extended period and then reintroducing large amounts of gluten all at once could become a problem if these microbes decrease in abundance and impact the host's ability to break down gluten. From these conclusions, it's safe to say that weekend gluten bombs are not a good idea for most people who go gluten free. If you intend to continue to eat gluten, you may want to keep a little in your diet from time to time to maintain a significant presence of the microbes that break it down since we are unable to. Finally, if you decide you are going to have gluten and haven't had it for a while, slowly introducing it may be a better approach than slamming down a 6 pack of brewskis and eating half of a pizza in a 3 hour period for the same reason.
Author's note: I personally limit my gluten exposure due to the potential effects on the microbiome. I'm not telling you whether or not you should eat gluten, I'm just giving advice on the appropriate ways to deal with reintroducing it if you have given it up for an extended period of time. Obviously this advice doesn't apply to people with celiac disease who, at this time, should never consume gluten.