For healthy life and aging, healthy lifestyles are as important as chronic diseases. Smoking, drinking and overwork have a similar impact on one's life as diabetes, and sedentary lifestyle and stress are more serious than hypertension and obesity. Contrary to the public knowledge, the types of food intake have a relatively small impact, and functional foods are effective only with a given optimal nutrition. Traditionally Koreans think certain types of foods (so-called 'health foods') have great effects on their health, and this idea resulted in confusion of terms health foods with functional foods. The effectiveness of functional foods should be evaluated based on human experiments. The in vitro and animal studies provide only preliminary evidence. Functional foods are between optimum nutrition and drug therapy in its effectiveness. Physicians should have appropriate knowledge on nutrition and functional foods and recommend them to their patients as they do for drug therapy.