CHAPTER 1 INTRODUCTION Synopsis This chapter briefly examines the relationship of diet to health and defines the concept of functional foods. A dietary supplement is considered as an addition to the diet to enhance health. Foods as medicine underpins the paradigm of functional foods. The recognition of medicinal mushrooms as functional foods or as dietary supplements is fully discussed especially in the concept of Chinese holistic medicine and modern immunology. In the developed nations of this world many causes of death or disability such as coronary heart disease, strokes, diabetes, atherosclerosis, obesity and certain forms of cancer can, in considerable part, be attributed to diet (Barasi, 1997). Poor food selection and restricted dietary intake can affect the nutritional status of an individual at any stage of life and can lead to impairment of long term health. Increasingly, scientific evidence is supporting the view that diet controls and modulates many functions of the human body and accordingly participates in the maintenance of the state of good health or homeostasis necessary to reduce the risk of many chronic diseases (Carter, 1993). Over the last few decades the science of nutrition has progressed from being largely epidemiologically based to the greater understanding of the physiological and genetic mechanisms by which diet and individual food components influence health and disease. It is indeed a paradox that nutrition is essential to support life but can also be considered as a causation of many chronic diseases.