Now that bread has made a comeback after the low-carb craze, it's getting hit with the gluten-free frenzy.

Hordes of people are giving up gluten, a protein found in wheat, barley and rye. The diet villain du jour, gluten is being blamed for everything from migraines and chronic fatigue to depression and infertility. It's being accused of making us fat and aggravating arthritis, acne and attention-deficit disorder.

Among the strongest advocates of a gluten-free diet are autism support groups and parents, including celebrity mom and author Jenny McCarthy.

Certainly, people with celiac disease, which affects an estimated 1 percent of Americans, need to strictly avoid gluten. Otherwise, this autoimmune disorder can damage the small intestine and interfere with absorption of nutrients. For celiac sufferers, a gluten-free diet is far from a fad: It is the only treatment.

What appears less clear is whether gluten can be blamed for other problems.

A gluten-free lifestyle

Carol Fenster has been gluten-free for 20 years, although she does not have celiac disease.

"I was told if you don't have celiac then you don't have a problem," said Fenster, who added that chronic sinus problems cleared up and she had more energy after she gave up gluten. She now conducts gluten-free cooking classes in Denver and has written seven gluten-free cookbooks, including her latest, "Gluten-Free Quick and Easy."

Experts say that the increased attention to gluten is a mixed blessing. On one hand, it may encourage more people to get tested for celiac, which still remains undiagnosed in about 97 percent of those Americans who have it. A diagnosis typically isn't made for about 10 years because the symptoms are mistaken for other conditions. Ironically, the current fervor may make proper diagnosis even trickier.

Starting a gluten-free diet before being tested for celiac may cause the gut to heal temporarily, which means an accurate diagnosis will be missed, said Dr. Joseph Murray, a celiac disease specialist at the Mayo Clinic in Rochester, Minn. He advised getting tested before treating yourself.

Self-diagnosis is rampant, probably because of increased awareness of the disease. People are now likelier to know someone with celiac and they relate to the disease's often vague symptoms, Murray said.

Complicating matters is the emergence of Internet laboratories promoting mail-order blood tests for gluten intolerance. Many of these tests are not an indication of what's going on at the intestinal level, said Dr. Carol Semrad, a celiac expert at the University of Chicago's Celiac Disease Center.

She's concerned that people will needlessly eliminate gluten, embracing a diet that is often difficult to follow.

Murray said there is little or no evidence to support a connection between gluten and other ailments, including autism. Even so, he said, there is nothing wrong with cutting out gluten as long as your diet is nutritionally complete.

"If you feel better, I can't argue with that, even if I don't have scientific proof as to why it seems to help," he said.

Going against the grain

Giving up gluten is challenging because the ingredient is prevalent in our food supply, often hidden in sauces, marinades, canned soups and other processed foods.

The diet also can be nutritionally challenging, said dietitian Dee Sandquist, a spokeswoman for the American Dietetic Association who specializes in celiac nutrition counseling. For example, many gluten-free baked goods are made with refined flours that are low in fiber and contain no iron, folic acid and other nutrients routinely added to wheat flour.

Experts say people on a gluten-free diet often lose weight because they typically reduce total carbohydrates and calories, not because gluten is inherently fattening.

Sometimes the overall quality of the diet improves because people start eating more fruits and vegetables and rely less on processed foods and sugary, refined grains.