The video shown below shows a doctor (yes, he is an actual M.D.) claiming that cow's milk should not be consumed by humans because it is downright harmful and directly linked to diseases like cancer. It has been rather popular and commonly shared on social medias in the past few months. Here, I'll address both of the main points made in this short video and show why he is wrong in giving out this kind of advice. Dr. Michael Klaper starts off the video by claiming that the purpose of cow's milk is to turn a small calf into a 400 lb (181 kg) cow and throughout the video repeats this as if it is strictly designed for calves and should not be consumed by humans. He is right that milk makes a calf grow as fast as possible but how does milk do this? Besides the fact that calves drink very large amounts of it (6-11 quarts, 1.5-2.75 gallons) per day, the contents of milk can also contribute to this growth. Milk is typically rich in nutrients including, as Dr. Kapler says, "hormones, lipids, protein, sodium, growth factors, [and] IGF." Lipids, protein, and sodium are nothing special to milk with each of these on average contributing about 3% (lipids), 3% (protein), and less than 1% (sodium) to milk's total weight. What really seems to be the problem, in Klaper's opinion, are the hormones (growth factors like IGF). Indeed, these growth factors do contribute to the calf's growth but Dr. Klaper is forgetting some basic biology here. 1) Hormones and growth factors are proteins. These proteins can be destroyed in various ways both before and after consumption. Firstly, milk is pasteurized. The high temperatures these proteins see during the pasteurization process can cause denaturation and subsequent inactivation of the protein. Second, in order for insulin-like growth factor (IGF) or any growth factor to affect you it also has to survive being broken down into its constitutive amino acids during digestion which, like most proteins, they do not. 1a) If you're wondering how these hormones can possibly affect calves when digestion renders most of them inactive, hormones typically play a role only very early in calf development when the intestinal tract is not fully mature and can allow things like hormones, growth factors, and antibodies to pass into the bloodstream (same with humans, but baby formula does not contain hormones or antibodies). Beyond that, milk's role in a calf's rapid growth is simply that it is a nutrient rich liquid that the calf consumes a very, very large amount of. 2) As Dr. Klaper keeps saying, this is cow's milk. The hormones in cow's milk is for baby cows. Hormones made by cows for cows simply do not work on humans. In order for a hormone to perform some action on a cell, it must first bind to a receptor and trigger a series of signaling pathways within the cell. Human cell receptors, however, do not bind to bovine growth hormones. So even if some small fraction of the growth hormones consumed survived both pasteurization and digestion and made it into the bloodstream, they can't trigger signals in our cells. (EDIT: Some cow hormones can't trigger human cells but some can. See below for more.) The other notable claim that Dr. Klaper makes in this video is that milk consumption is somehow linked to breast lumps in women and "man boobs" in men. The best available data, however, supports the idea that dairy consumption does not increase anyone's risk for any kind of cancer. http://www.ncbi.nlm.nih.gov/pubmed/16373955 http://www.ncbi.nlm.nih.gov/pubmed/15213021 http://www.ncbi.nlm.nih.gov/pubmed/12208895 http://www.ncbi.nlm.nih.gov/pubmed/22537215 So am I saying everyone should drink milk? No. What I am saying is that arguments like the one made by Dr. Klaper have no basis whatsoever in science and should not be taken as real health advice or used to promote certain agendas. If you don't want to drink milk or consume dairy for your own ethical or personal reasons, that's perfectly fine but doing so will probably not kill or harm you in any way we can measure. It is wrong to say otherwise under the guise of a medical authority.