The most well-known group is people who have celiac disease, an autoimmune disorder where eating gluten causes permanent damage to the small intestine. It affects about 1 in 100 people, according to the Celiac Disease Foundation.
But there's another group, too: people with gluten "intolerance," a.k.a. non-celiac gluten sensitivity (NCGS).
These people—who could account for 0.5 to 13 percent of the population according to two recent studies, published in Gastroenterology and The Psychiatric Quarterly—have most of the same symptoms of celiac disease but don't show any of the physiologic changes, like damage to the small intestine and malnutrition, De Latour says.
But unlike celiac disease, which can be definitively diagnosed, you can't know for sure if you have gluten intolerance, says De Latour.
"Gluten intolerance is not well understood in the medical community but it shouldn't be dismissed as psychological or just a fad," she says. "It's really a diagnosis of exclusion—once we've ruled out celiac through a blood test and an endoscopy, then NCGS is what we're left with."
There are some pretty major symptoms of gluten intolerance, however, that you won't be able to ignore—here are nine signs that you might be gluten intolerant.
1. You can't eat spaghetti without feeling sick or cramping.
Or bread. Or cupcakes. That's because stomach pain—nausea and abdominal cramps—after eating something containing gluten is the most common symptom of NCGS, says De Latour.
But it can be hard to connect the dots between what you ate and your pain. De Latour suggests keeping a detailed food journal to better identify triggers.
2. You're super bloated.
Bloating can be caused by so many things, from hormones to beans. But if you aren't properly digesting gluten, your stomach can definitely start to feel swollen and tender—especially after particularly glutinous meals, says De Latour.
3. Your skin is dry and flaky.
While there aren't any scientific studies to back this one up, lots of people with gluten sensitivity report having skin conditions, including extra-dry skin, rashes, acne, and patches of eczema.
4. You're losing weight without trying.
Involuntary weight loss is one of the primary symptoms of celiac disease, because when your intestines are damaged you aren't properly absorbing the food you eat, says Megan Patrick, M.D., a family medicine physician at UCHealth.
While NCGS doesn't damage a person's intestines, it can still lead to eating less due to associating so many foods with pain, which in turn can cause weight loss, says De Latour.
5. You just. Can't. Concentrate.
“Gluten sensitivity can be primarily, and at times exclusively, a neurological disease," reports Maios Hadjivassiliou, M.D., in a study published in The Lancet.
ADHD-type behaviors can be associated with gluten sensitivity. NCGS can decrease your ability to focus, says De Latour.
6. You feel down a lot of the time.
Mood changes, or feeling an increase in depression and/or anxiety after eating gluten-containing foods is a symptom in those with NCGS, says De Latour.
In fact, one 2014 study published in Alimentary Pharmacology & Therapeutics, found that gluten-intolerant subjects reported increased depression after just three days of eating gluten.
7. Your poops are kind of ridiculous.
Constipated all the time? Explosive diarrhea? Poo problems are another telltale sign of NCGS, says Patrick. Any time you see a significant change in your bowel movements that lasts more than a week, you should call your doctor, she adds.
8. You just can't remember anything.
One of the primary neurological symptoms reported by patients with gluten sensitivity is "brain fog" or just feeling like they can't think clearly and have trouble remembering things, says De Latour.
9. You're so tired you need a nap after your nap.
Your diet is one of the biggest factors in your energy levels, says De Latour.
You already know, for example, that eating junk makes you feel wasted while protein and veggies keeps you chugging all day—but that might extend to gluten, too. Many sufferers report their energy levels skyrocketing after giving up gluten, says De Latour.