Milk has evolved as a complete food for the mammalian nourishment of its young. However, research is unveiling an ever-accumulating range of bioactivities associated with milk substituents, emphasizing a role in programming human health. One good example is the increased complexity of carbohydrates in colostrum that may have a controlling influence on the selection of gut microbiota in infants at a very early stage of life. Milk can also affect processes outside the human gut - a proven example is the hypotensive effect of milk bioactive peptides through angiotensin-I-converting enzyme (ACE) inhibition. However, even more intriguing is the potential of milk constituents to influence immune and neural networks thereby affecting infection rates or mood, respectively. With the advent of bovine and human sequencing `omic' technologies, scientists are set to unlock many of the mysteries/mechanisms of how milk is good for you in ways that up to now were impossible to comprehend. (C) 2011 Elsevier Ltd. All rights reserved.