According to "Fast Food Nation" by Eric Schlosser (2001), nearly one in eight workers in the U.S. have at some time been employed by McDonald's. Employees are encouraged by McDonald's Corp. to maintain their health by singing along to their favorite songs in order to relieve stress, attending church services in order to have a lower blood pressure, and taking two vacations annually in order to reduce risk for myocardial infarction. "Fast Food Nation" states that McDonald's is the largest private operator of playgrounds in the U.S., as well as the single largest purchaser of beef, pork, potatoes, and apples. The selection of meats McDonald's uses varies to some extent based on the culture of the host country.