Doctors explain the signs that gluten isn’t your body’s friend.

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Celiac disease, an autoimmune disorder that makes it tough for the body to process gluten, has gotten a lot of attention in recent years. A slew of products beyond food has even sprung up to meet the corresponding demand for gluten-free foods. But while a growing number of people are self-diagnosing themselves with Celiac disease, how do you know if you legitimately have cause for concern?

First, a primer on what Celiac disease even is. When people with Celiac disease eat gluten—a protein that’s found in wheat, rye, barley, and the wheat-rye hybrid triticale—it triggers an immune response in their body that attacks their small intestine, Anton Bilchik, M.D., chief of medicine and chief of gastrointestinal research at California’s John Wayne Cancer Institute at Providence Saint John’s Health Center, tells SELF. This can damage the part of the small intestine that allows the body to absorb nutrients, making it difficult for a Celiac sufferer’s body to properly process food. Celiac disease is also hereditary, giving people who have a first-degree relative with Celiac disease a much greater risk of developing the disease themselves, Jamile Wakim-Fleming, M.D., a gastroenterologist and hepatologist at the Cleveland Clinic, tells SELF.

According to the Celiac Disease Foundation, an estimated one percent of the population worldwide has the disorder, and around 2.5 million Americans have undiagnosed cases of the illness. “It’s so much more common than people think it is—it’s quite astonishing,” says Bilchik.

But the actual signs of Celiac disease can be tough to pinpoint. “The typical signs and symptoms of the disease seem to be changing over time,” John Garber, M.D., a gastroenterologist with Massachusetts General Hospital, tells SELF. The classic signs used to be anemia (a condition where the body doesn’t have enough healthy red blood cells), diarrhea, and weight loss, Garber says, but “those ‘typical’ symptoms are now the less common ways the disease presents now.”

Now, Celiac sufferers can have a wide range of side effects. They may experience fatigue, constipation, low bone density, weight gain, bloating, fertility issues, and a foggy-headed feeling, the latter of which Garber says he’s seeing a lot more now. Vomiting, stomach pain, and even ADHD-like symptoms have also been linked to Celiac disease, Bilchik says. While people with Celiac disease can have several of these symptoms, they may also just have one. Basically, you could be tired all the time due to Celiac disease and not even know it.

Although some people with Celiac disease can have symptoms soon after eating a gluten-heavy meal, Garber says many won’t experience them for days or even weeks after having gluten. “The exposure to gluten doesn’t typically present an immediate set of symptoms,” he says. “Gluten is taken up in the intestine, and over time it gets presented to the immune system, causing a reaction.”

Luckily, there’s a way for doctors to tell if someone actually has Celiac disease or rule it out. There are two different blood tests doctors can perform that are pretty accurate, provided a person is eating gluten. “If a blood test comes back positive, it’s 75 percent likely that the patient has Celiac disease,” Garber says. (A negative blood test is 99 percent accurate, he says, making doctors very confident that a person does not have Celiac disease.)

At that point, doctors will typically recommend a biopsy of the small intestine to see if a person has internal symptoms of Celiac disease, Wakim-Fleming says. If they do, an official diagnosis is made. If they don’t, they’re typically told they have a gluten sensitivity, i.e. they may feel crummy after they have gluten but don’t have the autoimmune response typical of Celiac disease.

Unfortunately, the best way to treat Celiac disease is for a patient to avoid gluten in their diet, although Garber says new treatments are being tested out, including a “vaccine” to build up immunity to gluten and a pill to help break down the protein. “I tell my patients that even though right now the treatment is gluten-free diet, I think it will be very different in 10 years,” Garber says.

Watch: What Happens When You Give Up Gluten For A Month

13 Signs You Might Have Celiac Disease