Congratulations, Dr. Judith S. Stern, professor of Nutrition and Internal Medicine at the University of California! You're the first (though definitely not the last) science-type to come out publicly and call out Wii Fit. And not just call it out: call it baloney.
My understanding is that Nintendo is saying that if you track BMI, and by using this program, that you'll improve your BMI, or lower your BMI. I say baloney to that. In fact, I'm sure you'll see very little change in BMI. It's not just BMI you want to look at, but how fat you are.
When you are physically fit, you tend to replace fat with muscle, and your BMI probably won't change...I really think it's false and misleading.
Like I said, this is probably the first of many. Lucky for Judith she used "baloney", because the next scientist's going to have to use "devon", or "ham", and they just won't have the same ring to them.
Wii Fit: Interview with Dr. Judith Stern [GameSpy]