Feed your Defences 

Healthy bodies keep the immune system strong.  Strong immune systems keep the body healthy.  Both of these are completely and entirely dependent upon diet.  Poor diet equals poor immune function and poor health.  

Every dietary deficiency results in some form of immune compromise.  Malnutrition is the most common cause of immune deficiency.  Even in the "industrial world" where food is widely available to nearly everyone, undernutrition , defined as a lack of key nutrients with or without a lack of kilojoules, also results in immune compromise, especially for the elderly or hospitalised.  

Not surprisingly, the over-ingestion of kilojoules that leads to overweight and obesity can also lead to immune system compromise.  Thus maintaining a healthy body weight also promotes attaining and maintaining optimal immune potential.  

Powerful Protein

A lack of adequate protein in the diet, known as protein-energy malnutrition or PEM, is a common cause of immune dysfunction.  This is true for all of us, but especially in the young and elderly.  It is well known that protein deficiencies can stunt physical growth and mental development  and that these results are perpetuated into adulthood.  

Whatever the cause of insufficient dietary protein, the result is an increased risk of infection from adverse effects on both our innate (immediate, non-specific response to a challenge) and adaptive (learned, specific response from past exposures) immune capabilities.  

Poor protein quality or the conscious decision to avoid protein, especially animal protein can result in protein deficiency.  It is not manifested as a black or white situation, but rather one of degrees, causing the immune system to be generally weaker than it would be with a diet rich in high quality protein.  

It should also be noted that protein deficiencies of essential micronutrients, including vitamins A, B, D, E, folic acid, zinc, iron, copper and selenium.  Thus assuring micronutrient abundance is a critical, immune-building factor as well.