Lactoferrin, a protein found in breast milk, plays a crucial role in shaping the gut bacteria of newborns. A study looked at mice lacking lactoferrin during breastfeeding and found that they had more harmful bacteria in their guts, leading to an imbalance in their gut microbiota. This imbalance worsened in adult mice with obesity, colitis, and depression. The absence of lactoferrin disrupted the normal development of gut bacteria and made the gut more vulnerable to diseases like obesity and inflammatory bowel disease. By understanding how lactoferrin affects gut bacteria, we may be able to improve gut health in patients with these conditions.