"Feeding the animals according to the 1998 guidelines made the animals overweight," Park Seon-Deok, a member of the animal management team, was quoted as saying.
The zoo will decrease the amount of processed food, to which the animals have become accustomed, and increase the amount of natural materials.
"Horses, for example, like processed food better than grass, which is what they would be eating in the wild," Park said.
The zoo is also cutting portion sizes and instituting exercise programmes. In addition to healthier animals, it hopes to cut its annual 1.8 billion won (1.9 million dollar) feeding bill.