Do you try to steer clear of gluten – a composite of two proteins found in some cereal grains, including wheat and barley? If so, then you’re not alone. The number of people who’ve cut ties with gluten appears to have skyrocketed lately: food blogs are filling up with grain-free recipes, more and more people claim they are intolerant to gluten, and the mainstream media has upped its coverage of gluten-related stories. It’s become trendy to avoid gluten. Food manufacturers have responded to this trend by producing various gluten-free versions of common foods such as bread, cookies, and pasta, which many gluten-free consumers have embraced and incorporated into their dietary repertoire.
Some people argue that this widespread fear of gluten is completely unwarranted, whereas others say the opposite. Who should you listen to? What does the science say…?
Gluten-related pathology: An evolutionary perspective
Prior to the when the Agricultural Revolution started sweeping the globe some 12.000 years ago, gluten was not a part of the diet of any humans anywhere. Some of our Paleolithic ancestors, in particular our late Paleolithic ancestors, may have occasionally consumed some gluten-containing grains, but they obviously didn’t take in the massive amounts of bread and grain-based convenience foods that the modern man consumes.
This is very important to acknowledge, because it implies that there may have been inadequate time for “complete” adaptation to a gluten-rich nutritional environment to occur. This becomes especially apparent in light of the fact that in many parts of the world, it wasn’t until long after agriculture took hold in the Fertile Crescent that gluten-containing grains became a staple component of the diet.
What’s important to recognize is that our ancestors didn’t severely compromise their ability to survive and reproduce by eating gluten-containing foods. Quite the opposite. By consuming wheat, barley, and the like, they got more calories into their bodies: calories that fueled their bodily machineries, as well as their sexual and reproductive activities, as evidenced by the population boom that followed the Agricultural Revolution. They may have unwillingly compromised their health as well and increased their risk of developing various chronic illnesses, but seeing as these effects didn’t severely undermine their Darwinian fitness, they wouldn’t have been strongly selected against.
Natural selection may have favored those ancestors of ours who experienced the least amount of negative health effects from consuming a grain-based diet, seeing as these people had an edge in the evolutionary arms race; however, as mentioned earlier, seeing as the consumption of grains in most instances doesn’t severely compromise one’s Darwinian fitness, Darwin obviously didn’t rearrange the human body overnight so that it matches well with a grain-heavy diet. It may even be that certain gluten-induced physiological effects (e.g., activation of opioid receptors in the brain) are beneficial, fitness wise, in certain environmental contexts.
Besides adapting via changes in the DNA sequence, animals such as ourselves can adapt to their environment via epigenetic mechanisms, as well as via changes in their microbiomes. This provides us with flexibility, but it obviously doesn’t make us immune to any adverse effects brought about by environmental change.
Why hasn’t natural selection overpowered celiac disease in the parts of the world where people have been eating gluten-containing grains for many millennia?
The few cases when the consumption of cereal grains severely compromises Darwinian fitness are those that involve people with celiac disease – an autoimmune disease that is thought to affect about 1% of the population in the U.S. today. People with this disorder can’t eat gluten-containing foods. If they do, they experience a range of health issues, typically including diarrhea and flatulence. This raises a very important question: Why hasn’t natural selection eliminated – or at least severely reduced the prevalence of – alleles that are tightly linked with this disorder from the gene pools of populations that have been consuming gluten-containing grains for many millennia?
It might be that alleles that are thought to be detrimental in the context of celiac disease risk are beneficial in other ways, which is why they haven’t been weeded out; however, I don’t find this explanation completely satisfactory. Moreover, it doesn’t explain why research suggests that the prevalence of celiac disease has increased lately (1, 2).
Personally, I think the increasing prevalence of celiac disease can largely be attributed to the destruction of the human microbiome that has taken place over the most recent centuries, and in particular the most recent decades. By bombarding our guts with antibiotics and fast food, we’ve set ourselves up for autoimmunity.
Additionally, by largely abandoning many of the practices that traditional people used to prepare the grains they ate, we may have left ourselves more vulnerable to various grain-induced pathologies.
In other words, it seems likely that celiac disease, as well as certain other gluten-related disorders, are more common today than they were a hundred or even a thousand years ago, at least in some parts of the world.
It’s not only people with celiac disease who would be wise to keep gluten-containing foods at a distance
It’s often assumed that it’s only people with celiac disease who have a legitimate reason to avoid or limit their intake of gluten-containing foods. This assumption crumbles when it’s confronted with modern scientific research.
A wealth of scientific evidence indicates that it’s long past time to strongly consider restructuring the food pyramid so that grains are no longer at the bottom of it. It’s not just one substance in grains that is problematic. That said, seeing as this article is about gluten, we’ll keep the focus on gluten.
Here are some of the reasons why even people who don’t have celiac disease would be wise to think twice before they make gluten-containing foods a major part of their diet:
- Opioid peptides are formed during the digestion of gluten (3, 4). Repeated, chronic exposure to these peptides may negatively affect brain function, brain volume, and mental health, among other things (5, 6, 7). The fact that opioid peptides are produced during the digestion of gluten could help explain why we humans first took up agriculture and why some people find it difficult to give up gluten-containing grains (6). It could also help explain why some people, including myself, feel mentally foggy following the consumption of large quantities of gluten-containing grains.
- Several studies suggest that exposure to the gliadin fraction of gluten increases intestinal permeability in both celiac and non-celiac intestinal mucosa (8, 9, 10, 11)
- Recent randomized controlled trials suggest that exposure to glutes causes gastrointestinal issues in non-celiac patients with irritable bowel syndrome (12, 13).
- Studies suggest that gliadin exposure induces an immune response in both celiac and non-celiac individuals (8, 14, 15, 16).
- A 2015 in vitro study found that digested wheat gluten inhibits binding between leptin and its receptor (17).
With all of that being said, by itself, gluten is obviously not going to make you severely sick, unless of course you have celiac disease. Moreover, it’s important to point out that our bodies are extremely complex and varied and that it’s not that easy to investigate exactly what happens with a specific nutritional substance on its journey through our digestive systems and bodies. The fact that each and every one of us harbors a unique mix of bacteria – bacteria that are capable of degrading a wide variety of substances – further complicates this picture.
The problem with gluten-free varieties of common foods
As pointed out in the last section, gluten is just one of the many problematic compounds found in wheat, barley, and certain other cereal grains. A person who simply swaps out conventionally-produced bread, pasta, and the like with gluten-free varieties of these products will certainly reduce his intake of gluten; however, he will still be exposed to other troublesome compounds that are found in grain-based foods, as well as a lot of starch.
Instead of replacing gluten-containing grain products with gluten-free grain products, this person would probably have been better off replacing the grain-based foods he’s eating with high-quality animal source foods, fruits, and vegetables. This idea is supported by randomized controlled trials indicating that Paleolithic-type diets are healthier than grain-heavy diets (18, 19, 20).