There is a sizable, but still decidedly minority population that can benefit in terms of feeling better by excluding gluten, entirely or mostly, from their diets. There is a population -- an order of magnitude smaller -- for which it is vital to do so, and potentially even a matter of life and death. For everyone else, going gluten free is at best a fashion statement. Now, let's mill the details.
Gluten is generally described as a protein, which is basically correct. The compound is basically two proteins, gliadin and glutelin, bound together by starch (a carbohydrate). In nature, gliadin is found predominantly in the seeds of various grasses. We typically refer to the edible seeds of grasses as grains.
Grains, in turn, are made up of three parts: the bran or hull, the germ and the endosperm. Whole grains contains all three. Gluten is found in the endosperm, the principal part of the grain retained when grains are refined (and generally considered the least nutritious component). Consequently, gluten is present in grains such as wheat, rye and barley -- whether or not they are "whole."
If one adopts the long view of paleoanthropology, grasses are not native human food. We don't digest the stalks per se, and the seeds of most grasses are too small to bother with. Grains therefore entered the human diet only with the advent of agriculture in the Fertile Crescent some 12,000 years ago, when their domestication led to increases in seed size. The large seeds of wheat and other edible grains familiar today are not accidental, but the product of careful nurturing by humans over millennia of the grasses nature provided.
But still, only a dozen millennia, and while that's long enough for human selection to change grains, it's not a long time for natural selection to change humans. One of the important contextual considerations when attempting to explain health effects of gluten observed today is that this really is a recently introduced nutrient, foreign to the Stone Age diet that shaped our biological adaptations.
Those health effects are ever more prominently under scrutiny.
The most significant health problem associated with gluten consumption is, technically, gluten-sensitive enteropathy, long known as celiac disease, celiac sprue or non-tropical sprue. In this condition, the immune system mounts a response to gluten as if it were a dangerous invader, such as a pathogen. The resulting inflammation damages the intestinal lining, leading to malabsorption of diverse nutrients -- including both vitamins and minerals. Adverse effects can be severe, ranging from abdominal discomfort, to the manifestations of nutrient deficiencies, to an itchy rash, and over time, increased risk of intestinal cancer. Unaddressed, the condition and its complications can be lethal.
Along with celiac disease, there is also the milder "gluten sensitivity." This term is something of a catch-all, likely referring to various forms of intolerance and true allergy to gluten. The distinction between such conditions and celiac disease is that measurable antibodies to gluten are absent, as is observable damage to the lining and architecture of the intestine. Also absent is the nutrient malabsorption and increased risk of cancer. Recent insights, however, suggest the two conditions may overlap more than previously thought with regard to diverse symptoms.
There is good reason for gluten to loom large in current health lore: the numbers adversely affected by it are rising. To some extent, this is a product of something called "detection bias." The more aware and concerned the health care community is about any given health condition, the more we tend to look for it. The more one looks for any given condition, the more one tends to find it. In contrast, you don't tend to detect what you don't first consider, and for a long time, gluten sensitivity was under the proverbial radar.
Health professionals' sensitivity to gluten sensitivity accounts for some portion of the rising prevalence, but certainly not all. Studies based on blood kept in storage clearly indicate that actual rates of celiac disease have risen over recent decades, as much as four-fold in the past half a century. There is more to this story than better detection.
To my knowledge, no one knows for sure why this is happening, but there are theories. Against a backdrop of genetic vulnerability (both celiac disease and other forms of gluten sensitivity tend to run in families), there are new-age exposures to gluten that may be more likely to trigger immune system responses. In some cases, genetic modifications have increased the gluten content of wheat and other grains. It may be that genetic modifications are also introducing new nutrients into the diet, and some reactions to gluten may be primed by the company it is keeping.
There may also be an influence of nutrient combinations due to modern food processing. Gluten is a widely used texturizer. That it is found in wheat, barley, rye, triticale and possibly oat-containing products is expected. That it is found in everything from candy, to deli meats, to potato chips may be less so. Its use in all these foods is producing novel nutrient pairings, and perhaps these also function at times as an immune system trigger.
In the U.S. today, celiac disease is far from rare, affecting roughly 1 percent of the population at large. Gluten sensitivity affects 5 to 10 times as many. Celiac disease can be diagnosed by blood tests, biopsies or both -- so you will your clinician's help. The only truly reliable test for gluten sensitivity is a trial elimination of gluten to determine if symptoms wax and wane its intake. You can do this with the help of a nutrition expert, or all on your own.
Prevalent as it is, gluten sensitivity still only affects a minority in the general population -- but gluten preoccupation appears to affect many more. The potential adverse health effects of gluten in those sensitive to it have reverberated in cyberspace, creating the impression that gluten is a bona fide toxin, harmful to all. This is false; gluten is not "bad" for those tolerant of it, any more than peanuts are "bad" for people free of peanut allergy.
Also abounding are home-grown theories about health effects of gluten -- including the argument that going gluten free leads to weight loss. It might, but only because avoiding gluten means avoiding a lot of foods, which in turn tends to mean reducing calorie intake. That lowering calories leads to weight loss is less than an epiphany.
Going gluten free is easier than it once was due to better food labeling, more gluten-free products and ever better guidance, in print and online. But it is still quite hard, given the widespread use of gluten in packaged foods, under a wide variety of aliases. The effort is well-justified for those who are truly gluten-sensitive, but potentially much ado about nothing for others just caught up in the trend.
In addition, the exclusion of whole grain wheat, rye, barley and potentially oats from the diet might reduce overall diet quality and fiber intake. Again, a price worth paying when gluten avoidance is clearly necessary, but cost without benefit for others.
So, as noted at the start: there is a decidedly minority but still sizable -- and apparently growing -- population that can benefit from excluding gluten (entirely or mostly) from their diets. There is a population an order of magnitude smaller, also growing, for which it is vital to do so, and potentially even a matter of life and death.
For everyone else, going gluten free is at best a fashion statement, and at worst an unnecessary dietary restriction that results in folly. It reflects a tendency to ingest the ever proliferating pop-culture perspectives on diet and health, without first separating the wheat from the chaff.