Protein is a macronutrient you need in your diet every day for optimal health. In addition to building muscle mass, repairing damaged tissues and manufacturing hormones, your dietary protein protects you from infection by supporting your immune system. Your immune system includes blood cells, antibodies and other protein-rich molecules that help you both prevent and recover from infection.
Background
Your immune system is a complex network of white blood cells and proteins that recognize and attack foreign invaders such as bacteria, viruses and parasites. The protein you consume in your daily diet provides the building blocks these cells and molecules need to proliferate and to synthesize additional proteins to quell an invasion of pathogens. Your immune system, with the support of your dietary protein, protects you from infection through two mechanisms: innate immunity and acquired immunity.
Innate Immunity
Innate immunity describes the portion of your immune system you are born with. It is your first line of defense against infection and it includes protein-rich enzymes in your tears, saliva, nasal secretions and stomach acid, as well as the mechanical barrier afforded by your skin. In addition, several types of white blood cells act against pathogens that get past these initial protections. For example, neutrophils -– the most abundant of all your white blood cells -– attack and eat invading bacteria to protect you against infection. The cells and molecules of your innate immune system could not work properly without sufficient protein in your diet.
Acquired Immunity
Acquired, or adaptive, immunity is that which you develop as your body matures, and it functions in response to an invasion of a foreign substance, such as a pathogen. Your acquired immune system is further categorized as either cell-mediated or humoral. Cell-mediated immunity includes T cells, a white blood cell that secretes proteins to tightly regulate your immune response. Humoral immunity involves B cells, another white blood cell, responsible for the manufacture of antibodies. Together, these protein-rich immune molecules rely on your dietary protein to help guard against infection.
Considerations
While your daily diet should include at least 0.8 g of protein for each kilogram you weigh, consuming more than the amount you need to meet your requirements does not improve your protection against pathogens. The quality of your dietary protein matters, however. High-quality protein contributes all your essential amino acids, or the ones your body cannot manufacture. Therefore, your diet should include proteins from animal sources, such as meat, fish, milk products and eggs, all of which supply essential amino acids. Most plant proteins are missing at least one essential amino acid, but you can combine complementary plant sources -– such as rice with beans -– to provide the high-quality protein you need to help protect you against infection.
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