Gluten

Gluten is a binding protein found mostly in wheat, but also related grains such as barley and rye.

Gluten in mock meats

While there is a trend to reduce gluten in many mock meats, older mock meats still rely on gluten as an excellent binder for the other ingredients, or even as a main ingredient as protein.

Gluten is a grain protein, and is high in methionine which in moderation can compliment certain legume proteins (aside from soy which is already substantially complete) which are otherwise low in methionine. This could be important in diets with limited protein consumption -- However, it doesn't matter in a higher protein diet where all amino acids will be in surplus regardless. In those cases of a high protein diet, reduction of methionine can be wise due to health benefits of low methionine diets, so the only substantial benefit of gluten is structural (and in this regard, it's still hard to replace).

Gluten Nutritional Limitations

While part of a balanced plant based diet gluten has value, but gluten as a major source of protein (like an over-fixation on gluten based mock meants) can be unbalanced compared to legumes, lacking significant lysine. Purified gluten also lacks virtually any water and fat soluble nutrients, making it pale in comparison to other concentrated protein like tofu.

Products like tofurkey attempt to balance the structural benefits of gluten (and subjectively, the benefits on satiety) with the nutritional benefits of tofu by blending them. Other mock meats may integrate beans or other proteins to add lysine, and fortify the product.

Generally speaking, in cooking or formulating products, pure vital wheat gluten flour should be used in as small amounts as possible. This not only saves money (because gluten is expensive), but allows the food to contain more protein sources what come with higher amounts of micronutrients and better amino acid profiles. Gluten is a binder with few challengers, but use in moderation is ideal. Pure gluten seitan, while convenient and having fewer ingredients, doesn't make much sense as a vegan staple when 50% (or sometimes more) of the gluten can usually be quite easily substituted by another protein (pea protein, soy protein, pea or chickpea or white bean flour, etc.) without significant loss of cohesion.

Advocating for moderation in gluten should not be confused for advocacy of virtually gluten-free diets, which in contrast to the current trend are only known to be be necessary for celiacs or those suffering from extreme wheat allergies. It is good, however, that there are alternatives on the market.

Gluten Sensitivity and Celiac

Celiac affects to some degree roughly 1% of the world's population. It's caused by an immune reaction to the proteins in gluten in the small intestinal wall, and it can be definitively diagnosed. It's a serious issue for vegan advocacy because one dietary limitation can make people less likely to consider others, but also because common practice of limiting grain consumption to rice can make nutrition more complicated (a low protein grain intake means more protein has to come from elsewhere, and without gluten in mock meats that can be even more limiting).

Non-Celiac Gluten Sensitivity is much more controversial, and may have little or nothing to do with gluten. It's defined by a reported reaction to wheat where celiac and allergy have been ruled out. Due to unknown causes, it would be more appropriate to refer to it as non-celiac wheat sensitivity, and could range in cause from irritation by the insoluble fiber of whole wheat (roughly 10% by weight), to FODMAPs in most wheat products[1], to an allergic sensitivity to other compounds commonly in wheat or just in wheat bread itself unrelated to the wheat. In many of these cases, the purified glutens found in mock-meats should not be an issue, as is the case in experiments that have failed to show sensitivity in blinded trials for wheat sensitive people when exposed to pure gluten. In cases without formal diagnosis of celiac or allergy, it's important to look at the actual triggers and what they have in common, as opposed to making assumptions based on the popularity of trending conditions. As many people without celiac (another roughly 1%) may be broadly avoiding wheat and gluten ultimately without reason when the reaction is coming from something else related in a dietary sense to the assumed culprits. Stacking various food avoidances without careful consideration can have dangers, leading to poor diet -- or in the case of veganism, potentially recidivism (with or without nutritionally poor diet) due to the fatigue and psychological effects of multiple forms of restriction.

Gluten Panic

While there may be reason for some people to avoid large amounts of gluten if it's observed to aggravate digestive symptoms, or even relatively small amounts as in the case of celiac disease, there's also a general panic about gluten that extends beyond all reason where traces are so small they're literally undetectable to common tests of fall well below conservative recommendations for most celiacs.

For instance, Common soy sauce (like kikkoman[2]) has no detectible levels of gluten, which is due to hydrolysis during fermentation which breaks down the gluten[3]. While the manufacturers and healthcare sources will often council celiac patients away from these fermented soy sauces to wheat-free tamari options, there isn't any evidence that most of them contain enough gluten to be detectible let along aggravate symptoms in reasonable amounts even for those with celiac disease.

There are forms of soy sauce that are not fermented as long as traditional Japanese soy sauces, or may have wheat products added after fermentation as thickeners that may still be an issue, but broad avoidance of soy sauce is by an accounting of the evidence unnecessary.

Oats may also be avoided unnecessarily, under the assumption that all grains are terribly contaminated by gluten. It's true that for somebody with severe gluten intolerance oats could be a problem since the amount of gluten can vary greatly from harvest to harvest due to cross contamination of seed and fields, with up to two parts per thousand in some cases[4] (100 times greater that what is considered "gluten free"), even the higher end of contamination is not likely something anybody without very severe celiac would notice. Common recommendations are for celiacs to limits gluten to 10-50mg a day (sometimes up to 100mg[5]). This would translate to 5 to 50 grams of contaminated oats (as opposed to certified gluten free oats), roughly the weight of an instant oatmeal packet (although this would use up virtually the entire day's gluten tolerance). In practice many celiacs can tolerate levels higher than recommended, but dietary tracking can be difficult when gluten comes from many places in unpredictable amounts (if several sources by bad luck have an unpredictably high contamination level at the same time).

Even the high range indicates about 0.2% gluten in oats, compared to over 10% gluten in wheat bread.

Short of severe celiac, most people do not need to avoid grain or seek out gluten free labels to generally avoid gluten. Nor is there a clear need to avoid wheat starch when lower on an ingredients list (ranging from undetectable to 1% gluten, but rarely a main ingredient in a food) or hydrolyzed wheat protein/hydrolyzed gluten or hydrolyzed wheat flour.

Whole grains are an important and environmentally friendly source of nutrition, so should be sought out as part of a healthy diet -- and not just rice (which is lower in terms of nutrition by comparison to oats etc.). This is particularly true for plant based diets (which have important health benefits of their own) because additional limitations on top of avoiding animal products can make them more difficult to practice and limit options for nutrition.