When we say energy, we are referring to calories or your calorie count. So when we say energy balance, we mean that your calorie count has to be balanced. Now we all know that when you eat too much, then you will gain much more calories. So if you want to maintain a healthy weight, then your calorie count should be just right. Also, exercise is also very important because if you intake more calories, then you have to make sure to burn it off through exercise so that you can maintain your balanced calorie count.