Enzymes, hormones, antibodies and other biologically active substances in the human body are composed of proteins. Antibodies are immunoglobulins with defense functions, which have the effect of increasing the body’s resistance and protecting it from bacteria and viruses.
–Public Dietitian

Proteins are the main raw materials for the renewal and repair of human tissues. Every day year-round about 3% of the proteins in the human body need to be renewed, such as intestinal mucosal cells are renewed every 6 days on average.
–Public Nutritionist

Protein supplementation can provide an extremely favorable material basis for the synthesis of antioxidant enzymes and the play of antioxidant damage, increase enzyme activity, improve the antioxidant capacity of the intestinal tract, and more effectively scavenge the production of free radicals and reduce the damage caused by free radicals to the cell membrane of the mucosa.
–Yu, X., Wang, Y., Li, P. B., Jin, H., Protective effects of proteins on the intestinal mucosal barrier of semi-starved rats[A]. Parenteral and Enteral Nutrition, 2008, 15(6):331

Protein is an important component of antibodies, an important immune substance of the organism. Antibodies can resist the invasion of foreign microorganisms and other harmful substances.
–Sun Yuanming, Food Nutrition (Second Edition) [M]. Beijing, China Agricultural University Press, 2010:59

In vitro studies have confirmed that lactoferrin has a certain inhibitory and killing effect on a variety of microorganisms.
–Yang Yuexin, Li Ning, Guidelines for the Application of Nutritional Functional Ingredients [M]. Beijing, Peking University Medical Press, 2011:42

The strength of the body’s ability to resist disease is related to the amount of antibodies in the body, and the generation of antibodies has a close relationship with the nutritional status of proteins, so the nutritional status of proteins plays an important role in the body’s ability to resist disease.
–Li Qingya, Zhang Song, Nutritionist’s Handbook [M]. Beijing, People’s Military Medical Press, 2.10: 28

The effect of malnutrition on immune function was initially studied in children with protein-energy malnutrition (PEM), and it is clear that their immune function is adversely affected in a number of ways, and that epithelial integrity is compromised in malnourished patients, leading to greater susceptibility to invasive microorganisms. Several studies have also demonstrated that neutrophil activity is reduced, and with regard to acquired immunity, there is a decrease in the number of circulating T-cells, and B-cells, accompanied by loss of T-cell function and attenuation of antibody responses, one of the main adverse effects of PEM is increased susceptibility to infectious diseases, further loss of micronutrients due to stressful temporal phase reactions and immune activation.
–Modern Nutrition