To avoid eating too much food at mealtime when dieting, use smaller plates, bowls and cups. It is instinct to fill up your plate so if you use smaller dishes, you will eat less food. Your mind will also let your stomach know you are full since you see a full plate when eating.
To understand nutrition's importance, you need to gain an understanding of how your body functions. It is made up of many complex systems: the neural, the gastro-intestinal, the lymphatic, the endocrine, the muscular-skeletal and so on. These all dovetail and work together as a whole. This complex "wholeness" is what you need to gain a good sense of, in order to meet your body's nutritonal needs.
When making your plates of food, be sure to use a very small plate. The small plate will be full so it will trick the brain into believing that you are consuming more food than you actually are. This means that you will feel full after consuming less food.