or take-out menus, shampoo bottles, apartment listings, the tag of your shirt,

on a hammer, as a lower back tattoo, or in your friend's resume.

Next time someone starts telling you about their newfound freedom from gluten,

here are some questions you can ask,

and the well-informed answers that your friend,

being a reasonable individual making educated dietary choices,

and by no means just following the latest diet craze, will tell you.

What is gluten?

Gluten is an insoluble protein composite

made up of two proteins named gliadin and glutenin.

Where might you encounter gluten?

Gluten is found in certain grains, particularly wheat, rye and barley.

What has gluten been doing for the previous entirety of human history,

and why do you suddenly care about it?

Gluten is responsible for the elastic consistency of dough

and the chewiness of foods made from wheat flour,

like bread and pasta.

For some people, these foods cause problems,

namely wheat allergy, celiac disease, and non-celiac gluten sensitivity.

Wheat allergy is an uncommon condition

that occurs when a person's immune system

mounts an allergic response to wheat proteins,

leading to mild problems, and in rare cases,

a potential dangerous reaction called anaphylaxis.

Celiac disease is an inherited disease,

in which eating foods with gluten

leads to inflammation and damage of the lining of the small intestine.

This impairs intestinal function,

leading to problems like belly pain, bloating, gas, diarrhea,

weight loss, skin rash, bone problems like osteoporosis,

iron deficiency, small stature, infertility, fatigue and depression.

Untreated, celiac disease increases the risk

of developing certain types of cancer.

Celiac disease is present in one in every 100 to 200 persons in the U.S.

When blood tests suggest the possibility of celiac,

the diagnosis is confirmed with a biopsy.

The most effective treatment is a gluten-free diet,

which helps heal intestinal damage and improve symptoms.

Some people don't have celiac disease or a wheat allergy,

but still experience symptoms when they eat foods with gluten.

These people have non-celiac gluten sensitivity.

They experience painful gut symptoms

and suffer from fatigue, brain fog, joint pain or skin rash.

A gluten-free diet typically helps with these symptoms.

So how many people actually have this gluten sensitivity you speak of?

Gluten sensitivity's occurrence in the general population is unclear,

but likely much more common than wheat allergy or celiac disease.

Diagnosis is based on the development of symptoms,

the absence of wheat allergy and celiac disease,

and subsequent improvement on a gluten-free diet.

There's no reliable blood or tissue test,

partly because gluten sensitivity isn't a single disease,

and has a number of different possible causes.

For example, it may be the case

that gluten can activate the immune system in the small intestine,

or cause it to become leaky.

But sometimes, people claiming gluten sensitivity

are actually sensitive not to wheat proteins,

but sugars found in wheat and other foods, called fructans.

The human intestine can't break down or absorb fructans,

so they make their way to the large intestine or colon,

where they're fermented by bacteria,

producing short-chain fatty acids and gases.

This leads to unpleasant symptoms in some people with bowel problems.

Another possible explanation behind gluten sensitivity is the nocebo effect.

This occurs when a person believes something will cause problems,

and because of that belief, it does.

It's the opposite of the more well-known and much more fortuitous placebo effect.

Given how much bad press gluten is getting in the media,

the nocebo response may play a role

for some people who think they're sensitive to gluten.

For all these reasons,

it's clear that the problems people develop

when they eat wheat and other grains aren't exclusively due to gluten.

So a better name than non-celiac gluten sensitivty

might be wheat intolerance.

Okay, so if instead of telling people you're gluten-free,

you had to tell them you're wheat intolerant,

would I still have to hear about it as often as I do now?

Your gluten sensitivity sensitivity

is coming off as wheat intolerance intolerance.