Clearly it's not the food they ate that made the difference but a subtler level of energy—the level where mood, emotions, motivation, aspirations and beliefs exist. It takes energy to keep this level of life going, so when we say that someone is giving off negative energy, what we really mean is that at the subtle level of mind and body, negative beliefs are consuming energy and turning it into negative actions, words and thoughts.
The first thing to realize is that you are in control of your own energy. I know it doesn't feel that way sometimes. Depression can take hold like an invading germ; anxiety can cause fear to leap out of nowhere; anger can simmer like a pot on the stove. Yet these conditions do not define you, and in fact you can begin to use basic energy—the kind that comes from food, air, loving relationships, nature's beauty and the flow of creativity—for your own good. All these sources of energy are available to you all the time. They are part of your birthright; they connect you to the flow of life, which is constantly renewing itself.
How efficiently are you leading your life?