HALLOWELL, Maine — Jonathan McCullum was in perfect health at 155 pounds when he left last summer to spend the school year as an exchange student in Egypt. But when he returned home to Maine just four months later, the 5-foot-9 teenager weighed a mere 97 pounds and was so weak that he struggled to carry his baggage or climb a flight of stairs. Doctors said he was at risk for a heart attack. Mr. McCullum says he was denied sufficient food while staying with a family of Coptic Christians, who fast for more than 200 days a year, a regimen unmatched by other Christians.

But he does not view the experience as a culture clash. Rather, he said, it reflected mean and stingy treatment by his host family, whose broken English made it difficult to communicate.

“The weight loss concerned me, but I wanted to stick out the whole year,” he said in an interview at his family’s home outside Augusta. Friends and teachers at his English-speaking school in Egypt urged him to change his host family, but he stayed put after being told the other home was in a dangerous neighborhood of Alexandria. After returning to America, he was hospitalized for nearly two weeks. The 17-year-old has regained about 20 pounds, but his parents say he’s not the same boy he was when he left under the auspices of AFS Intercultural Programs.

“He was outgoing, a straight-A student, very athletic. Now, he’s less spontaneous and more subdued,” his mother, Elizabeth McCullum, said, adding that she was shocked when she met her son at the airport on January 9 and saw he had lost one-third his weight. Jonathan McCullum’s parents said the exchange program should have warned them that students placed with Coptic families would be subject to dietary restrictions. Marlene Baker, communications director at AFS headquarters in New York, declined to discuss Mr. McCullum’s experience. She referred calls to the program’s lawyer in Portland, Patricia Peard, who said she could not comment on Mr. McCullum’s case because of the potential for a lawsuit.

Mr. McCullum said his host family gave him only meager amounts of food, and his condition worsened during the last seven weeks, when the family observed a fast limiting the amount of animal protein he was given.

The host family was a couple with two younger boys and a daughter who was in America on an AFS exchange. Mr. McCullum said the parents gave him the smallest food portions, hid treats in their bedroom and complained that the cost of his upkeep was more than they spent for their daughter when she was home.

The host father, Shaker Hanna, rejected Mr. McCullum’s story as “a lie,” suggesting that he made it up because his parents were hoping to recover some of the money they paid for his stay as compensation.

“The truth is, the boy we hosted for nearly six months was eating for an hour and a half at every meal. The amount of food he ate at each meal was equal to six people,” Mr. Hanna said.