Nutrition has a predominant and recognizable role in health management. Nutrigenetics is the science that identifies and characterizes gene variants associated with differential response to nutrients and relating this variation to variable disease states especially cancer. This arises from the epidemiological fact that cancer accounts for a high proportion of total morbidity and mortality in adults throughout the world. There is much evidence to support that genetic factors play a key role in the development of cancer; these genetic factors such as DNA instability and gene alterations are affected by nutrition. Nutrition may also lead to aberrant DNA methylation, which in turn contributes to carcinogenesis. The aim of this work is to clarify the basic knowledge about the vital role of nutrition-related genes in various disease states, especially cancer, and to identify nutrigenetics as a new concept that could highlight the relation between nutrition and gene expression. This may help to understand the mechanism and pathogenesis of cancer. The cause of cancer is a complex interplay mechanism of genetic and environmental factors. Dietary nutrient intake is an essential environmental factor and there is a marked variation in cancer development with the same dietary intake between individuals. This could be explained by the variation in their genetic polymorphisms, which leads to emergence of the concept of nutrigenomics and nutrigenetics.