Ting Zhang

College of Food Science and Engineering, Jilin University,

The intestine is the central site for digestion and absorption of nutrients and is also an important barrier that resists the invasion of harmful substances and maintains homeostasis in the internal environment. Increasing data show that intestinal diseases have one of the highest incidence rates globally, causing a tremendous burden on human health. Intestinal diseases such as ulcerative colitis and Crohn's disease, increase intestinal permeability, destroy mucous membranes and intestinal barriers, and promote harmful substances and pathogens to enter the blood. Gut microbiota imbalance is also strongly associated with intestinal inflammation, and the diversity of the gut microbiota is markedly reduced in individuals with intestinal disease compared to that in healthy individuals. In a damaged gut, the ratio of beneficial to harmful bacteria is significantly reduced, triggering a decrease in some beneficial metabolites, such as short-chain fatty acids (SCFAs), further exacerbating intestinal diseases. Therefore, repairing the intestinal barrier and regulating gut microbiota are key targets for treating and preventing gastrointestinal inflammation and metabolic diseases.

The European Society for Clinical Nutrition and Metabolism suggested that adults with inflammatory bowel disease (IBD) should increase their protein intake to 1.2–1.5 g/kg body weight/day compared to that consumed by the healthy population (0.83 g/kg body weight/day) Furthermore, nutritional availability, especially that of proteins, is crucial during the illness treatment period. Eggs are the main high-quality proteins that are usually consumed in daily life, especially egg white proteins (EWP), which are currently one of the main sources of novel bioactive peptides. Eggs are among the most easily digestible proteins. The rich amino acid composition, high protein digestibility, easy availability, and low cost make it possible to use EWP as an ingredient in nutritional supplements. Although the current studies on EWP in the intestine are focused both on the basic intestinal structure and function, we summarize three possible mechanisms by which EWP regulates the intestinal barrier based on existing cell and animal research: (1) restoring the damaged intestinal barrier to its intact structure, (2) regulating the intestinal immune system and reducing the degree of inflammatory response and oxidative damage process in vivo, and (3) increasing the relative abundance of beneficial bacteria and metabolites.

EWP and its bioactive peptides have been proven to regulate the intestinal barrier and gut microbiota. These potential health benefits mainly involve the intake of proteins that may provide essential amino acids to the body to ensure the intake of nutrients by damaged intestinal cells. The antioxidant and anti-inflammatory activities of bioactive peptides may affect the relational pathways in the body. These pathways produce complex interactions that regulate the intestinal barrier function. However, the structure of bioactive peptides prepared from EWP is diverse, and the length of the peptide chain differs, which may affect regulation efficiency. Therefore, understanding the interaction between the structure of the EWP peptide and target pathway proteins may be an important research direction to reveal the repair mechanism in the intestinal barrier.