I used to eat alot but now i decided to eat less, will i get fat?

currently i'm on a 'eat little' diet. I think i'm going to keep this going, because i'm laying on the sofa all day and i can't exercise. The reason why is because my knee went out of place and i can't really do anything. So if i eat 2 slices of bread and yoghurt will i get fatter or thinner? I don't get it...