Practice observing through awareness what your body needs.
Do you need a heavier breakfast? Do you need to consume meat? Do you need to quiet your environment while eating? Observe how your body feels when you are consuming your food. This is not something we are used to doing in our rushed culture.
If a diet is not working for you, if your body is reacting to different foods, try becoming more aware. Your body is an excellent communicator – are you willing to listen to it?