As part of its ongoing efforts to promote every single Pokémon out there, The Pokémon Company has shared special content dedicated to Chansey:
Did you know? The egg Chansey carries is not only delicious but also packed with nutrition. It’s used as a high-class cooking ingredient. This species was once very slow. To protect their eggs from other creatures, these Pokémon became able to flee quickly.
Source: The Pokémon Company