From Smithsonian:
In 1933, James Hilton, a British novelist who read about travels in Yunnan Province in National Geographic magazine, wrote a novel called Lost Horizon, which describes a mythical kingdom set far, far away from the rest of time: Shangri-La. Three years later, Frank Capra turned Hilton’s paperback best-seller into a film. The place entered our lexicon as an earthly retreat from the worries of modern civilization.
The fictional Shangri-La appears to be an amalgam of Yunnan Province and Tibet. But the people of the Hunza Valley in Pakistan became, in the American mind, the closest thing to the real-life incarnations of the people of Shangri-La. The Hunzakut people reportedly lived to be 100 and had a practically illness-free existence in an inaccessible mountain valley. Paeans to healthy Hunza proliferated. President Eisenhower’s cardiologist reported that Hunza men could eat 3,000 apricots in one sitting. In 1960, the Journal of the American Medical Association published an editorial extolling the virtues of the Hunza diet as a harbinger of hope for human longevity and modern medicine.
More here.