Only thing that since they aren't made to be worn outside, the soles will probably wear down faster so they won't last as long as if you just wore them inside. I discovered that in college when I decided I wanted to wear my slippers for a while instead of my regular shoes.
Oh and I guess the new thing are inside boots because I've been seeing them a lot of places and I've been wanting to buy some. I saw some really cute knitted ones the other day.
You can't out-exercise poor eating habits.