When I founded our celiac center nearly 20 years ago, writers couldn’t spell “celiac,” and very few people had ever heard the word “gluten.”

One of our primary goals has been to advance awareness of celiac disease to improve the quality of life for people with gluten-related disorders, and I’ve been amazed to see what has happened in 20 years. Most people have now heard of gluten, but many have a pretty poor understanding of what it is and how it fits into a healthy diet.

An ancient and complex protein, gluten is a major component of wheat. It helps bread to rise and gives it a characteristic chewy texture. Similar proteins called secalin and hordein are found in barley and rye. We lump the three together as the only proteins we can’t digest and call this gluten.

For people with celiac disease, a lifelong disorder, these proteins wreak havoc on the small intestine. For the rest of us, it’s a different story.

1. Our bodies are not meant to process gluten, so no one should eat it.

Many people now vilify wheat as unfit for human consumption. Eating it “raises blood sugar levels, causes immunoreactive problems, inhibits the absorption of important minerals, and aggravates our intestines,” in the words of prominent bioethicist and futurist blogger George Dvorksy. This “sensational science” is fertile terrain for TV shows such as “Dr. Oz” and books that identify gluten as the villain of the 21st century. Gluten has been blamed for many diseases outside gluten-related disorders, and therefore some people have suggested that it should be completely banned from the human diet.

It is true that our bodies do not have the proper enzymes to break down the complex proteins found in gluten. The immune system spots gluten as an invader and goes into battle mode to get rid of it. But here’s the key: In most people, the immune system is able to “clean up” the gluten invasion, and then it’s back to business as usual.

For the approximately 1 percent of humans with celiac disease, the immune system can’t handle the cleanup. Instead, it goes into overdrive, producing autoantibodies that attack the tissue in the small intestine, leading to inflammation and tissue destruction. This leads to malabsorption of nutrients, which causes myriad symptoms, gastrointestinal and otherwise, in people with this autoimmune disorder.

Other people affected by wheat allergy or non-celiac gluten sensitivity also may find that their bodies react inappropriately after they eat gluten-containing grains. But epidemiological studies, including our 2003 study in the United States, show that the vast majority of us tolerate gluten without any problem. The fact that about 1 percent of the population is affected by celiac disease, while almost 100 percent of humankind is exposed to gluten-containing grains, is evidence that these grains are safe for most people. After all, our species has evolved during the past 10,000 years eating gluten-containing grains.

2. Cutting gluten from your diet is beneficial, even if you don’t have celiac disease.

Approximately 1 in 4 U.S. consumers think that going gluten-free is good for everyone, according to the NDP Group, a market research organization. The same group reports that about 11 percent of U.S. households eat gluten-free.

These people are probably following advice such as: “Eliminating wheat is the easiest and most effective step you can take to safeguard your health and trim your waistline,” from William Davis, the physician of “Wheat Belly” fame.

But only about 400,000 Americans have been diagnosed with celiac disease. This is a small fraction of the 3 million people in the United States who have it; the rest remain undiagnosed. Wheat allergy sufferers number about 0.03 percent of the U.S. population. Because medicine has no reliable test for the condition, the number of people with non-celiac gluten sensitivity has not yet been established. Our center recently estimated it at 6 percent of the U.S. population, but it is only our best guess until we develop a biomarker to identify the condition.

For most of us, a gluten-free diet is not a naturally healthier diet. If you give up gluten-containing cookies, cakes and beer, and replace them with gluten-free cookies, cakes and beer, you will not lose weight or feel better. But while avoiding gluten itself won’t help, giving up many of the processed foods that contain it will. If you stop eating fried foods, highly processed foods and foods high in sugar, and replace them with fresh fruits, vegetables, olive oil and protein from lean meat, eggs, seafood, nuts and beans (essentially, the Mediterranean diet), you will definitely feel better, unless you have an unidentified underlying condition.

People who do undertake a gluten-free diet should work with a registered dietitian to make sure they’re getting all the vitamins and micronutrients they need.

3. Gluten sensitivity doesn’t really exist.

About five or six years ago, we began to see a new phenomenon in our clinic: people who reacted poorly to gluten but had none of the diagnostic or histological markers for celiac disease. Eventually, our group published a paper calling the condition “non-celiac gluten sensitivity” or “gluten sensitivity.”

As celebrities from Gwyneth Paltrow to Novak Djokovic have espoused the “benefits” of going gluten-free, though, there’s been some resistance to the idea of gluten sensitivity. At this point, enough people have gotten on board with ditching gluten that it’s being mocked as a “fad” diet by people such as cookbook author and culinary historian Clifford Wright.

Based on conflicting studies, the existence of gluten sensitivity has been challenged in the press. And until recently, the terms “celiac disease” and “gluten sensitivity” had been used interchangeably in medical literature, as Amy Brown noted in a 2012 article in Expert Review in Gastroenterology & Hepatology.

But although many of the symptoms are similar, the two conditions are very different metabolically. In non-celiac gluten sensitivity, we don’t see the same intestinal inflammation that we see in people with celiac disease. Also, some people with gluten sensitivity can tolerate small amounts of gluten, which is never the case with celiac disease.

4. People with celiac disease can eat a little bit of gluten.

A group of scientists from St. Bartholomew’s Hospital in London published a study in 1988 concluding that adult celiac patients could safely consume a low-gluten diet, as opposed to a gluten-free one. Unfortunately, that misconception is still with us.

We now know this is not true, since we have pretty solid evidence that traces of gluten can be as harmful as large amounts, even if the clinical consequences don’t materialize until years later. People with celiac disease must avoid gluten at all costs. While eliminating the “big items” (pizza, pasta, cookies, beer, bagels, etc.) is painful but relatively easy, avoiding the traces of gluten found in many processed foods (gluten is a cheap and efficient filler) can be much more difficult. It takes only a tiny crumb of bread to set the autoimmune machinery into motion, creating the intestinal damage that leads to symptoms and nutrient malabsorption.

This is what makes the gluten-free diet so tricky, especially outside the controlled environment of your own kitchen. Think about celiac kids in day-care centers or classrooms (craft projects and cupcakes), and celiac diners in restaurants, social settings and traveling away from home. People with celiac disease and parents of children with the condition must be vigilant about what they put in their mouths every day in a way that the rest of us don’t need to be.

What makes this clinical chameleon even trickier is that you can have celiac disease (the intestinal inflammation and malabsorption) and not exhibit any symptoms, gastrointestinal or otherwise, for a long time. Meanwhile, damage to your intestine continues and could lead to the development of related conditions and, in extremely rare cases, intestinal lymphoma. The only way to identify these asymptomatic patients is through blood tests and an intestinal biopsy.

5. If you have celiac disease as a child, you will outgrow it.

This question comes up often in our celiac clinic because of the lingering misconception that celiac disease is a pediatric condition. In the 1930s and ’40s, children diagnosed with this mysterious gastrointestinal disease were fed a banana-based diet. The mortality rate was high, but the lucky children who survived were told that they could resume eating wheat after a period of time. This led to the idea that you could outgrow celiac disease. Years later, with advanced diagnostic tools, many of those “banana babies” were rediagnosed with celiac disease.

In the 1950s, a Dutch pediatrician named Willem-Karel Dicke determined that wheat flour was responsible for the symptoms he saw in his young patients. After watching the mortality rate of children with celiac disease drop during World War II, Dicke suspected that the decline might be related to the scarcity of bread at that time. Still, it would be decades before the notion that you can outgrow celiac disease was challenged.

In 1958, Cyrus Rubin determined that pediatric and adult celiac were the same condition. With the development of the first diagnostic tools in the 1970s and blood-screening tests in the 1990s, the diagnostic rates for children and adults increased.

But the real breakthrough came in the 1990s, when researchers determined that celiac disease is not a food allergy or an intolerance, but a gluten-triggered autoimmune disease and, therefore, a condition patients cannot outgrow.

Another milestone was when we determined that people can develop celiac disease at any time in their lives, even into old age. Now we know it is a lifelong condition, and the best medical intervention we have is a gluten-free diet.

Alessio Fasano is the founder and director of the Center for Celiac Research & Treatment at Massachusetts General Hospital in Boston and the author of “Gluten Freedom.” This column was distributed by The Washington Post, where it first appeared.