Dr. Butler said some of Cuba’s shortcomings may actually improve its health profile. “Because they don’t have up-to-date cars, they tend to have to exercise more by walking,” he said. “And they may not have a surfeit of food, which keeps them from problems like obesity, but they’re not starving, either.”

Cuban markets are not always well stocked, but city streets are dotted with hot dog and ice cream vendors. Bellies are full, but such food can cause problems in the future, as it has in the United States.

Dr. Butler has just completed a study that shows it is possible that because of the epidemic of obesity in children, “this may be the first generation of Americans to live less long than their parents.”

There could be one great leveler for Cubans and Americans. While all Cubans have at least minimal free access to doctors, more than 45 million Americans lack basic health insurance. Many are reluctant to seek early treatment they cannot afford, Dr. Butler said. Instead, they wait to be admitted to an emergency room.

“I know Americans tend to be skeptical,” he said, “but health and education are two achievements of the Cuban revolution, and they deserve some credit despite the government’s poor record on human rights.”

Universal health care has long given the Cuban regime bragging rights, though there is growing concern about the future. In the decades that Cuba drew financial and military support from the Soviet Union, Mr. Castro poured resources into medical education, creating the largest medical school in Latin America and turning out thousands of doctors to practice around the world.

But that changed after the collapse of the Soviets, according to Cuban defectors like Dr. Leonel Cordova. By the time Dr. Cordova started practicing in 1992, equipment and drugs were already becoming scarce. He said he was assigned to a four-block neighborhood in Havana Province where he was supposed to care for about 600 people.