Dogs use their powerful noses to help humans detect danger, including sniffing for drugs, bombs and even cancer, but some canines are now assisting their families in a unique way: They sniff out gluten.

They’re trained to help some of the 3 million Americans who have celiac disease, an autoimmune disorder. Affected people must avoid gluten, a protein found in wheat, rye and barley, because it will damage their small intestine. Symptoms include diarrhea, abdominal pain, bloating and anemia.

For Evelyn Lapadat, a 13-year-old girl who lives in Indiana, celiac disease leaves her with joint pain, stiffness and fatigue. She’s sensitive to even the tiniest amount of gluten.

Despite a dramatic diet change, gluten kept sneaking into her life.

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“If someone puts a crouton on a salad in the back at a restaurant and takes if off and says, 'Oops, this needs to be gluten-free,' and brings Evelyn her salad, previously, she would say, 'Looks good to me,' eat it, be sick for three days," her mom, Wendy, told TODAY.

That rarely happens now, thanks to Zeus, an Australian shepherd. Zeus is by Evelyn's side throughout the day at school, checking her hands and sniffing her food. If he raises his paw, it means he smells gluten. If he turns his head, the item is safe.

“I haven't gotten sick in a really long time and it's like a really big relief,” Evelyn said.

“I feel like I don't have to be a complete control freak anymore. I feel like he can be a control freak for us,” her mom added.

Ciara Gavin didn't train Zeus, but teaches other dogs like him to detect gluten. We visited Colorado Springs to meet her newest trainee, Maggie. During a key exercise, one of Gavin’s hands contained gluten powder, the other didn’t. Every time Maggie sniffed the gluten hand, she was rewarded.

Once she's ready, Maggie will help a 4-year-old with celiac disease who suffers stroke-like symptoms. Gavin said such dogs are ideal for homes that are already gluten-free. They can smell food, shampoo and soap to detect if gluten is brought in.

Accuracy is harder in a public place, like a mall or restaurant, where gluten is all over.

"It's not a way to make life easier. It's just a way to make life a little bit safer,” Gavin said. “This is a last line of defense, not a first line of defense."

For Evelyn, having Zeus around has been life-changing: Her inflammation problems have practically vanished. Her doctor says a gluten-sniffing dog is unusual, but it's exciting to think about the potential.

Experts warn there are no national guidelines for training gluten-detecting dogs, so families should do their research and closely examine the companies and their standards.