Whether fact or fad, or a bit of both, gluten avoidance has become a way of life for millions of Americans. According to a study by the Center for Celiac Research at Massachusetts General Hospital, nearly one out of 133 Americans suffers from celiac disease, a genetic autoimmune disorder, in which all foods with gluten, found in wheat and other grains, must be avoided. According to the center’s figures, another 18 million people, or 6 percent of the population, have gluten sensitivity; symptoms may range from gastrointestinal issues to behavioral problems to joint pain and osteoporosis. And then there are countless people avoiding gluten because they think it’s simply a healthier way to eat, or because they believe it will result in weight loss.

“It’s a real thing, not a fad,” says Melinda Dennis, nutrition coordinator at Beth Israel Deaconess Medical Center’s Celiac Center. Both celiac disease and gluten sensitivity have increased dramatically, and not just because testing has improved, she says. “People are being diagnosed more — and it’s more prevalent.”

There are a number of possible explanations for the increase. One theory holds that the wheat we eat today is different from yesteryear. Says Dennis, “There is now a controversy on how wheat has changed or not changed. The controversy is: Has it really changed? But what we can say is that we’re eating more of it — more than 100 years ago or even 50 years ago.”

In addition, gluten is hidden in a number of condiments and prepared foods, so gluten-free shoppers have become dedicated label-readers.

Dennis herself was diagnosed with celiac disease 20 years ago. Still, she acknowledges that some people may be avoiding gluten unnecessarily, and that they could be putting themselves at risk. Anyone who goes on a gluten-free diet, she says, should seek the guidance of a nutritionist, lest they end up with deficiencies in nutrients and fiber that could leave them feeling even worse.

Popular diet doctors certainly haven’t failed to pick up on the trend. The newest book from Arthur Agatston, creator of the South Beach Diet, is “The South Beach Diet Gluten Solution.” And William Davis’s best-selling “Wheat Belly” promises in its subtitle to “Lose the Wheat, Lose the Weight.” But a gluten-free diet isn’t a weight-loss regimen per se; after all, that gluten-free brownie can still be loaded with fat, sugar, and calories.

Chefs, restaurateurs, and food manufacturers aren’t in a position to know — or care — why customers are demanding gluten-free choices. In a field where sensitivity to customer need is paramount, they realize that having gluten-free options available just makes good business sense.

While some chefs hinted off the record at their personal skepticism about gluten-free diets, most are in the business of accommodating diners. “I learned a while back that it’s not my job to tell people what to eat or how to enjoy it,” says Dave Becker, chef and owner of Sweet Basil in Needham. Lydia Shire, chef and owner of Scampo, adds, “We have done everything we can to please [customers who avoid gluten]. There’s nothing I wouldn’t stop at doing.”

For diners with celiac disease, it’s not sufficient that the food is free of gluten; if it’s prepared in a kitchen where wheat products are used, there’s the risk of cross contamination. The measures sometimes seem extreme, but no restaurant wants to run the risk of a lawsuit or negative publicity that might result if a customer were to accidentally ingest gluten.

At Back Deck restaurant, burgers and sandwiches can be ordered on gluten-free buns made by Curtis Street Bakers, a Somerville wholesaler of gluten-free baked goods that supplies area coffee shops and Tufts University. But Back Deck chef and owner Paul Sussman goes a step further, making sure that the burger itself is cooked on a grill that’s never used for items that might contain gluten. “And nothing goes in our fryolater except potatoes,” says Sussman, who explains that frying a breaded item could contaminate the oil.