Overall Evidence for Milk-Derived Proteins and Peptides in Blood after Digestion: A Systematic Review

Abstract Context Milk and dairy products are rich in protein components, including bioactive peptides and proteins that may play crucial roles in influencing human health. Despite extensive research on the nutritional profile and bioactive components of milk, there is no consensus on the presence or absence of milk-derived proteins or peptides in the blood post-consumption of milk or dairy products. Many studies have identified milk-derived proteins or peptides from blood, but there is no existing catalog of all the proteins and peptides found from the blood matrix. Various types of study design exist, but they consider several types of animals, feed sources, and other variables. In addition, there is currently no existing catalog, or review, encompassing all milk-derived proteins and peptides found in blood, or the methods for identifying them from a blood matrix. Objective The objective of this article was to create a comprehensive list of milk-derived proteins and peptides detected in blood after digestion of milk or other dairy products. Data Sources A search strategy was developed and adapted for each database searched (Web of Science and PubMed) and for the gray literature search (Google Scholar). Additionally, the references for all review papers identified by the searches were screened for potential inclusion. Data Extraction Studies were reviewed for relevance by at least 2 authors independently. Relevant studies underwent data extraction and were evaluated for risk of bias by 1 researcher. The articles were managed in COVIDENCE. Data extraction and risk-of-bias assessments were performed in Excel. Data Analysis A total of 108 studies were included, of which 102 detected milk-derived proteins or peptides in blood, mainly intact immunoglobulin G (IgG), β-lactoglobulin (BLG), α-lactalbumin (ALA), and casein peptides. Conclusion This review will inform researchers about (i) established milk-derived proteins and peptides that can be found in blood from consuming dairy, (ii) bioactive milk-derived peptides with potential to exert bioactivity systemically, and (iii) what methods are optimal for use in identifying absorbed proteins and peptides. Systematic Review Registration PROSPERO registration No. CRD42023476956.