According to Nintendo guru Shigeru Miyamoto, while Wii Fit is fun, it's no substitute for exercise. Miyamoto advises you to get out of the house and do some real exercises sometimes.
“Spending too long, staying in and playing any video game is not good,” said Miyamoto. “I always tell my children to get out on a sunny day and I, myself, went jogging in Central Park yesterday. But I do my stretching on Wii Fit. They work together.”
So there you have it: Play games but go out riding your bike sometimes too; Shigeru says!