“It was like doping,” Winsberg, 42, said. “Suddenly I was running six-minute miles instead of nine-minute miles. Before I had placed in the bottom third in triathlons. Four weeks gluten free, and I placed second in a triathlon. It was like reverse aging. I went from feeling 38 to 28 to 18.”

Winsberg’s transformation did not surprise Dr. John Reasoner, a medical director with the United States Olympic Committee.

“In six to eight weeks, if they’ve followed the diet, it’s night and day,” he said.

Reasoner said that symptoms of celiac disease were often subtle but came at a high cost for athletes who expected maximum performance. Dave Hahn, who has reached the Mount Everest summit 10 times, said he found he had the disease after he became “inexplicably weak” on his second trip to the peak in 1999.

Hahn was the climbing leader on a search expedition for the remains of the Everest pioneer George Mallory, who had disappeared on the mountain in 1924. The search was successful, but Hahn struggled. Then 37, he had become anemic. Perilously weak and short of breath on summit day, he had to depend on his climbing partner to make it off the summit alive.

“It was a huge source of shame which made me feel like I had to get to the bottom of the health problems that I’d been ignoring for so long,” Hahn said.

He returned to the doctor he had seen eight years before for chronic gastrointestinal problems, common in celiacs, and this time she diagnosed the disease.

Hahn said he had difficulty adjusting to the gluten-free diet.

“I got stronger again without question, and you don’t really expect that in your late 30s,” he said. “I had gotten to the point up high and in the cold where I completely ran out of gas.”