Pokémon GO is a mobile game. The game is based on catching Pokémons and to catch them you have to go outside and walk a lot to find them. So basically it makes players have some physical activity while playing the mobile game.
The game became very popular when it was released on July 6th, 2016. According to Clinic Compare, if you catch 100 Pokémons per day while playing Pokémon GO, it would take you about 3 days to shed 1 pound (0.45 kg) of weight, that is 10 pounds (4.5 kg) per month.
This computation is based on some average values. Your gender, age, the place where you play the game and Pokémon density may change the results.