Balance. The best diet is relatively high in protein. You should avoid processed sugars and starches, although many natural complex carbs, such as potatoes, are fine. It is advisable to remain caffeine-free, as caffeine makes you more sensitive to low glucose levels.
Watch sugars. Simple sugars and processed carbs should be avoided or limited. This includes any flour product. The fine grind makes absorption quick, and spikes your blood sugar which increases Insulin and promotes weight gain. Good fats such as olive oil and coconut oil are fine in sensible amounts. Eat a rainbow of organic vegetables and just enough protein. Complex starches are fine.