Celiac disease makes up a tiny fraction of the cases of gluten intolerance, which as much as 20% of the population of, say, the USA may have. (Source: Dangerous Grains, by James Braly and Ron Hoggan) Then add in actual wheat allergies. That's a lot of people.
So yes, people can have allergies to all sorts of things. I've been there (long story; currently it's only cow's milk I have to avoid) and it's not fun.
I'm going to have to partially dispute you. I'll get to the point, but first let's define clearly, what is an allergy, an intolerance and what's coeliac disease.
Some raw numbers, wheat (gluten) allergies affect less than 1% of the population (it's something like .48%). It's not something you can hide, you either swell up and stop breathing when you come in contact with it or you don't. It's actually hard to find in adults as most people grow out of it when they enter puberty. If you don't die within a short time from eating wheat (without treatment) due to an IgE antibody surge, you aren't allergic -- full stop. (yes, there are emergent allergies that occur later in life, gluten allergies are generally not considered to be in the class of those types of allergies). http://en.wikipedia.org/wiki/IgE
Wheat (gluten) intolerance is more prevalent. But so are most food intolerances. For example, it's generally considered that 3/4 of the adult population of the U.S. has a dairy intolerance. Intolerance != allergy. You can eat foods you are intolerant to. It might give you an upset stomach or bad gas or some such, maybe diarrhea and a really bad headache. But by those symptoms most of us are intolerant of high fiber diets, coffee and all forms of strong alcohol. It might be worse, like dizziness or some such, but if you don't have IgE antibodies in your system after contact with the suspect food it's not an allergy. In other words, probably 100% of the population is intolerant of some food some of the time. People often mistake "allergic" with "intolerant". Allergies are far more severe and critical than intolerance. Intolerance comes from a lack of an ability to process a given external agent due to some genetic predisposition -- like how many East Asians can't process alcohol properly or MSG makes my Aunt get a headache.
Coeliac disease occurs in about .75% of the population (as identified so far). It is a distinct and different disease from gluten allergies and gluten intolerances. Coeliac disease is an autoimmune disorder where the body destroys the lining (the villi) of the intestine as a response to the presence of the byproduct of gluten after it's been improperly modified by a faulty enzyme causing an IgA antibody flareup in the gut. It's only now really being diagnosed as it is easily confused with other bowel diseases prior (like IBS or Ulcerative colitis or granulomatous among others). Recent IgA antibody tests do a pretty good job of positively identifying the disease (but you have to be on a gluten rich diet for it to work, otherwise you'll have no antibodies to test for!). The number may grow, but probably not much, even wildly high estimates put it at under 3% of very localized, genetically predisposed populations. Whatever the case, it presents as a chronic disease, not an allergy. You don't eat wheat, then blow up, stop breathing and die. Your intestine slowly rots away, you become malnourished and your feces turns white.
Likewise, food intolerance != Coeliac disease != food allergy. The three things are different. You may as well bundle people with sun allergies and who have dry skin from harsh soap into your numbers if you are going to do that. The only common factor is that the causative agent is the same -- wheat. But even if you add up all the numbers of people with wheat allergies and people with coeliac disease, you likely end up with something less than 3-4% of the general population.
"Dangerous Grains" is an interesting book. But if all you look for is a duck, suddenly everything starts to look like a duck. I'd caution anyone from self-diagnosing based on descriptions of layman oriented symptoms from a book written to popularize an interesting theory. Many things cause precisely the same symptoms as gluten intolerance (and visa-versa). Dangerous Grains, while an great way to popularize recent science with the layman, is not the same as medical science.
"If you don't die within a short time from eating wheat (without treatment) due to an IgE antibody surge, you aren't allergic -- full stop."
What? With all due respect, this is a ridiculous definition of "allergic" and not at all the standard one. Are all the people with, say, pollen allergies not really allergic if all they get is a runny nose? I feel lousy when I eat anything containing cow's milk, and I have high IgE antibody levels for it, but I don't die. Nonetheless, that is an allergy.
I'm well aware of the difference between an allergy and an intolerance, as I thought I made clear by mentioning gluten intolerance as well as wheat allergy.
Dangerous Grains makes and cites plenty of references to the published literature, so it's hardly your average pop-sci book. A major point of it was that celiac disease is only one way in which gluten intolerance, that is, inability to properly digest gluten, can manifest.
Immunoglobulin E antibody presence is the only meaningful definition for "allergic" in the literature. You are right, there are different degrees of immune system response w/r to IgE response. But no IgE? Not allergic -- probably intolerant -- may have something else.
Lots of things people say/think they are allergic to, they are actually intolerant of.
I'm not putting down Dangerous Grains, only cautioning that many people improperly self-diagnose. The authors are recognized practitioners in allergy medicine. I forget some of the the terms off-hand, but mistaken self-diagnosis when learning about new medical topics is sometimes called the "medical school student syndrome".
Just because many of the easily observable symptoms of Coeliac disease are commonly found in any random selection of population, does not mean that Coeliac disease is common. It doesn't help that most of the symptoms may or may not even be present!
But really here's the list of symptoms: Abdominal pain, Abdominal distention, bloating, gas, indigestion, Constipation, Decreased appetite (may also be increased or unchanged), Diarrhea -- chronic or occasional, Lactose intolerance (common upon diagnosis, usually goes away following treatment), Nausea and vomiting, Stools that float, are foul smelling, bloody, or “fatty”, unexplained weight loss (although people can be overweight or of normal weight upon diagnosis), Anemia (low blood count), Bone and joint pain, Bone disease (osteoporosis, kyphoscoliosis, fracture), Breathlessness (due to anemia), Bruising easily, Dental enamel defects and discoloration, Depression, Fatigue, Growth delay in children, Hair loss, Hypoglycemia (low blood sugar), Irritability and behavioral changes, Malnutrition, Mouth ulcers, Muscle cramps, Nosebleed, Seizures, Short stature, unexplained Skin disorders (dermatitis herpetiformis)
Swelling, general or abdominal, Vitamin or mineral deficiency, single or multiple nutrient (for example, iron, folate, vitamin K), Type-1 diabestes, autoimmune thyroid disease, autoimmune liver disease, rheumatoid arthritis, addison's disease, sjogren's syndrome.
Almost everybody I know has half of these symptoms half of the time -- and the ones that are less common are from something that's not CD (hair loss? how about Rad poisoning. Short children? Pituitary irregularity. Mouth ulcers? How about being a skank in High School?)
Here, let's try some example differentials:
Patient is 28, Female, Caucasian, blood pressure is normal, pulse is normal, height and weight are average.
Symptoms: Anemic, Bloating, Constipated, Abdominal Pain, Nausea and vomiting, Bruising easily, Fatigue, irritability and behavioral changes, muscle cramps, swelling, vitamin D and Calcium deficiency in lab work.
Does she have a) Lupus? b) PMS? c) or one of the .5% of the adult population with CD? (hint, it's never Lupus).
How about this:
Patient is 62, Female, Caucasian, BP is elevated, pulse is elevated, height is below average and weight are average.
Symptoms: Anemic, Indigestion, Occasional Diarrhea, Bone and Joint Pain, Bone disease (osteoporosis), Bruises easily, Dental discoloration, Fatigue, Hair loss, Hypoglycemia, Malnutrition, Short Stature, unexplained, Hives, Vitamin and mineral deficiency.
Does she have a) Lupus? b) Old, eats a crap diet of mostly snack foods, works a high stress sedentary job and drinks lots of coffee and tea and just starting eating a high fiber diet for the first time in her life? c) one of the .5% of the adult population with CD?
Or let's try another:
Patient is 34, Male, Caucasian, BP is normal, pulse is elevated, height is average, weight is above average.
Symptoms: Thyroid disease, type 1 diabetes, fatigue, vomiting, foul smelling stools, diarrhea, irritability, nosebleeds, vitamin and mineral deficiency.
Does he have a) Lupus? b) Has hereditary Grave's disease, is fat, eats a crap diet of pizza, candy and Jolt, has poor social skills, and just ate a bad piece of three day old pepperoni and we should check to see if he has sepsis and swab for known food-borne pathogens? c) one of the .5% of the adult population with CD?
My point is that the observable presentation symptoms for CD are crap. They could be symptoms for anything. Hence the caution on self-diagnosis. It also doesn't mean people should go out of their way to inconvenience themselves to avoid grain products and food with gluten in it because they get bloated on occasion or have stinky poo.
So yes, people can have allergies to all sorts of things. I've been there (long story; currently it's only cow's milk I have to avoid) and it's not fun.