Several years ago I was involved in a fitness challenge. I took it seriously and really hammered on every aspect.
One of my best secrets was to sweat before I ate anything. Breakfast, lunch, dinner, and especially snacks.
The quality and quantity of your diet is important- it's far better to get away form heavy processed sugars and carbs and get a better balance.
But almost regardless of this, if you do enough interval work (snatches, swings, hindu squats, walking- anything) to build up a sweat - just get a good bead of sweat going, then eat, your metabolic rate increases and you don't immediately turn your food into fat.
Short, sweet, and key.