Best diet is to simply follow the Sunnah in eating and drinking. Do some research on what foods and drinks were consumed by Rasoolullaah صلى الله عليه وسلم. Also, follow the Sunnah method: eating on the floor, eating with three fingers, eating in moderation: one third of the stomach for food, one third for water, one third for air. Only eat when you're hungry. Only drink when you're thirsty. Only sleep when you're tired. There is no such thing as "breakfast, lunch and supper." You eat when you're hungry. If you're not hungry in the morning, for example, then don't eat. Don't force yourself to eat just because the Kuffaar have this thing called "breakfast". When you're hungry, eat. If you're not hungry, don't eat. Don't eat until you're "full". Eat until you are no longer hungry. Same with drinking.
Also, kick out any "vegetarian" or "vegan" diets. It's against the Sunnah. Rasoolullaah صلى الله عليه وسلم ate meat. Only the Kaafirs believe that meat is bad for you, because Shaytaan excreted that idea into their skulls. There is only goodness in following the Sunnah and there is only harm in going against it.
Was-Salaam.