My favorite food is fresh homemade bread. Nothing can surpass biting into that first slice, crust still crisp from the oven, a nutty aroma suffusing the senses, a lucent note of butter or honey wafting through the chewy cloud of carefully nurtured carbohydrate.
But lately bread, or, more specifically, one of its constituents, has come under scrutiny. It has been blamed for causing or contributing to a growing list of diseases and shunned by an increasingly large segment of the health-conscious public. That component is gluten. But what, precisely, is gluten, and why has it acquired such a bad reputation? Is that reputation even warranted? Let's find out!
Instant Plant, Just Add Water
To understand what gluten is, we first need to understand seeds. Before seeds developed, back when runaway photosynthesis was throwing the atmosphere off-kilter, plants reproduced using spores. Spores have a lot of disadvantages – they're small (containing only a few cells, relatively speaking), flimsy, and don't have a lot of nutrients to kickstart growth of the young plant. Seeds were a major innovation, in that they allowed the plant to develop leaves and roots before it germinated, and they gave the mother plant a chance to pack a lunch for its offspring, a store of nutrients called the endosperm.
Managing an endosperm is tricky – plants have to manage a trade-off between cramming as many nutrients as possible into the seed, but still making them easy to access when they're needed for germination. The major nutrients a plant needs to grow can be remembered with the onomatopoeic acronym “SPONCH,” or sulfur, phosphorous, oxygen, nitrogen, and hydrogen. These are organized into the four major macromolecules, carbohydrates (which contain carbon, hydrogen, and oxygen), fats (likewise), proteins (which are nitrogen-based and sometimes require sulfur), and nucleic acids like DNA (which are phosphorus-based).
Fats and carbohydrates are the main source of energy for a growing seedling, and it they are fairly easily compacted into starch (as in most grains) or converted to energy-rich oils (as in most nuts). Proteins are harder to deal with. Functional proteins are delicate or have elaborate three-dimensional structures that take up a lot of space and don't pack easily; to get around this problem, plants will instead tuck the building blocks of proteins, amino acids, into more compact and robust storage proteins.
This is where gluten comes in. Referring to gluten as a single protein is a bit of a misnomer, because it's actually made up of two different proteins: glutenin and gliadin (which themselves are best described as classes of proteins, but let's stay out of that particular rabbit hole). Both of these protein classes serve the same purpose, to hang on to amino acids until the growing seedling needs to turn them into something more useful. However, they also share a chemistry that so far appears to be unique – when exposed to water and mechanical action, glutenin and gliadin bind to one another and form a large protein network. This network traps carbon dioxide and water, causing the formation of bubbles when dough is baked and keeping bread moist afterward.
So Why Is It a Problem?
For a small but evidently growing segment of the population who suffers from celiac disease, consumption of glutens produces symptoms ranging severity from abdominal cramps and discomfort to gastrointestinal distress (to put it euphemistically) to malnutrition due to chronic inflammation of the intestinal lining.
As it's currently understood, celiac disease is an autoimmune disorder, caused by the body's overzealous response to gliadin. It is currently understood that sections of gliadin are incompletely digested. In people with celiac disease, these sections draw the attention of transglutaminases, enzymes that stitch proteins together. After this step, the gliadins are targeted by the body as foreign and potentially dangerous, leading to a typical immune response: inflammation, followed by the influx of water into the digestive tract to flush the would-be “invader” out.
However, research on a different pathway has suggested that gliadin can trigger responses in people who do not suffer from celiac disease. An in vitro study by celiac disease researchers at the University of Maryland found that gliadin can bind to receptors in the cells that line the intestines, triggering the release of a hormone called zonulin. The zonulin release causes the spaces between the cells to get wider, making the gut “leaky.” In people with celiac disease, the zonulin release is higher, causing a wider separation. This allows gliadin to get in past the the first layer of cells, where only extremely short fragments of proteins are supposed to end up. This, as mentioned above, riles up the immune system and leads to an unpleasant reaction.
This research is notable in that it found that even normal intestinal cells exhibit this zonulin response. So does this mean gluten is dangerous for everyone? The authors of the study note that there's a major difference in the gliadin response between those who suffer from celiac disease and those who do not. In non-sufferers, the magnitude of the zonulin release is both smaller and shorter-lived; it only lasted around an hour in their experiment. Furthermore, the intensity of the response is also dependent on how much gliadin is present – chowing down on three bagels is probably a less intelligent decision (for several reasons) than eating a piece of toast.
But what about the people who don't have celiac disease but still seem to experience unpleasant side-effects after eating wheat products? Unfortunately, the answer to this question is much less clear. As recently as 2009, researchers publishing a review in the journal Nature have referred to these “gluten sensitivities” as a “no-man's land.” People with a diagnosed gluten sensitivity tend to show partial symptoms of celiac disease or carry the genetic markers associated with celiac. Other people with gluten sensitivities are diagnosed with irritable bowel syndrome (IBS), which can be caused by any of a large number of dietary factors. Experiments on IBS patients with apparent gluten sensitivity have found that the culprit is not gluten at all, but a group of carbohydrates called FODMAPs, which are also present in large quantities in wheat and which healthy people usually have no trouble digesting.
However, while this research suggests that the segment of the population sensitive to gluten is larger than just those with celiac disease, there is still little evidence to suggest that moderate gluten consumption is harmful to those who don't experience gastric discomfort after eating it. Gluten's current reputation appears to be the result of faulty reasoning. First, the assumption is frequently made that because gluten is harmful to those with gluten sensitivities, it's harmful to everyone, rather than understanding that extreme reactions to gluten are the result of a dysfunctional immune system. Under this reasoning, peanuts, tree nuts, and shellfish are also dangerous to consume. Furthermore, as gluten-free diets take off due to the increasing perception that glutens are harmful, we're starting to see examples of the “nocebo” effect, where thinking something is bad for you can manifest in actual negative symptoms.
On the whole, criticisms of gluten as inherently hazardous or poisonous are probably hyperbolic – like everything, bread is best enjoyed in moderation. Fears not allayed? Join me next time, where we talk about how we can harness biochemistry to our advantage when working with wheat flour.
Drago S, et al. 2006. Gliadin, zonulin, and gut permeability: Effects on celiac and non-celiac intestinal mucosa and intestinal cell lines. Scandinavian Journal of Gastroenterology.
Verdu EF et al. 2009. "Between Celiac Disease and Irritable Bowel Syndrome: The "No Man's Land of Gluten Sensitivity." Am J Gastroenterol.