It is safe to say that the majority of people understand that what they eat has some effect upon their health. Nearly anyone can observe that after eating too much junk food, they tend to have an upset stomach, or that after they eat a large meal, they feel tired. Many people in the United States believe that a bowl of chicken soup can help alleviate the common cold, and that "an apple a day will keep the doctor away." In China, herbs have long been used to treat various maladies. The drugs ephedrine and pseudoephedrine, found in many over-the-counter cold remedies, are derived from the "ma huang" plant which has been used in China to treat colds and flu for more than five thousand years (Mindell, 1992). Research has confirmed relationships between the foods humans ingest and affects upon their health. However, most of the research is very particular in nature, looking closely at the effects of specific vitamins, minerals, and other food components upon health.
Vitamin C in particular appears to have received much attention, especially as it pertains to the flu and the common cold. One study showed a slight reduction in symptoms due to the common cold in individuals who received a supplement of 80mg of vitamin C, but no reduction in susceptibility to the common cold (Baird, Hughes, Wilson, Davies, Howard, 1979). However another study provided evidence that for individuals under acute physical stress, daily supplements of 0.6 to 1.0 g of vitamin C considerably reduced the incidence of the common cold (Hemila, 1996).
There appears to be very little research with regards to general diet and health, and that which relates to diet and occurrence of the flu and/or the common cold seems to be nonexistent, or at best difficult to find.