After reading number of books on a good diet practices, I believe most of it could be boiled down to two key concepts.
Calorie Density
The idea is that to leave healthy long live one should adopt Calorie Restriction on their diet. One example of this is the Okinawan diet. Calorie density is roughly defined as the numbers of calories per gram of the food. Hence the idea is that you'll get full faster by simple consuming large quantity/mass of low calorie food.
Nutrient Density
This second concept, coined by Dr. Fuhrman, is getting food that have higher nutrient content with respect to the calorie/energy content. In other word nutrient-dense foods are those foods that provide substantial amounts of vitamins and minerals and relatively few calorie.
These two concepts are few of the reason why low-glycemic-index carbohydrates are the preferable choice for the health concious people. Glycemic Index tells us how much our blood sugar rises after we eat a particular kind of carbohydrate food. Increase of blood sugar leads to increase of insulin level, which have been linked to host of problems.
The usual choice of low-GI carbohydrates are the Whole Grain products such as brown rice and whole-wheat bread. Aside the benefit of low-GI, the bran from whole grain is rich in dietary fiber, essential fatty-acids, various antioxidant and, not to forget, Niacin (Vit. B3) which has been proven (in pharmacological doses) to reverse atherosclerosis by reducing total cholesterol, triglycerides, very-low-density lipoprotein (VLDL), and low-density lipoprotein (LDL), and increasing high-density lipoprotein (HDL).
