Colostrum, the first form of milk produced by mammals immediately following delivery, is rich in immunoglobulins, growth factors, and antimicrobial peptides. Its use to support the small intestine is primarily supported by scientific evidence, particularly in the context of gut health, permeability, and immune function. Several studies have demonstrated that bovine colostrum supplementation can enhance gut barrier function by reducing intestinal permeability, sometimes referred to as "leaky gut." This is especially relevant in clinical scenarios such as athletes experiencing increased gut permeability due to intense exercise, patients with inflammatory bowel diseases, or those suffering from infectious diarrhea.

Mechanistically, colostrum contains bioactive molecules (e.g., lactoferrin, IgG, growth factors like IGF-1 and TGF-β) that promote intestinal cell growth, repair, and mucosal immunity. Randomized controlled trials in both adults and children have found that colostrum can decrease gut permeability and help restore normal intestinal function after injury or infection. However, while the body of evidence is promising, most studies are small, heterogeneous, and sometimes industry-funded. Therefore, the strength of evidence is moderate (rated 3/5), supporting its use as an adjunct for short-term gut support, but more large-scale, independent, and long-term studies are needed to confirm its efficacy and safety.