"Soprattutto, fate attenzione alla dieta."

Translation: Above all, watch your diet.

[ThinkerDreamer]

Can someone tell me why "Above all, be careful with the diet" is wrong? I was thinking it meant something like: Be careful when you're dieting (or you could become unhealthy).

[dnovinc]

I think it should be accepted.

[dnovinc]

Is "fare attenzione" only followed by preposition "a" [fare attenzione a qualcosa/qualcuno] or are there instances when we can use a different preposition?