Building on the belief that raw milk is the stuff of greatness, a writer for Strength and Health, John McCallum, penned articles touting raw milk as the way to grow (later compiled into the book The Complete Keys to Progress. Randall J. Strossen, editor of that book, took that idea a step further, and suggested that everyone drink a gallon of milk a day and do his 20 rep squat program. It's my understanding that Strossen merely repackaged McCallum's ideas about milk and squats, which would make sense, as it was still legal to produce and transport raw milk in the US in 1965 (when McCallum penned the book). In retrospect, I'd imagine the fact that Pat Casey (the first guy to bench 600 lbs raw) and Doug Hepburn (the first guy to bench 500 raw) drank 6 quarts of milk a day factored into the belief that a gallon of milk a day is the way to super-strength as well, as it really drove home McCallum's suppositions.
No matter who invented it or why it became so popular, the adoption of that diet in this century is fucking ridiculous for a variety of reasons, starting with the fact that it's impossible to purchase raw milk easily in the US, and pasteurized and homogenized milk borders on indigestible for most people. Whereas raw milk merely ferments in your intestines (which actually makes it better for you), pasteurized milk putrefies. (Bieler, 211) Additionally, pasteurized milk is shown to be among the top three food allergies, and has symptoms ranging from ear infection and bad breath to asthma, admonial cramping, diarrhea, croup, and asthma, even in people who are lactose tolerant.(Audette, 58) Throw into the mix the fact that even skim milk contains 205g of sugar per gallon (and has a higher GI than fatty milks), and you've got a fucking recipe for disaster. Thus, in straining the shit out of your digestive system, you're getting a paltry 145g of protein for your efforts, not all of which will be digested, due to the fact that the fat molecules in homogenized milk are broken down into smaller parts and become a stealth delivery system for the proteins that puts them directly into your bloodstream, causing allergies. Pasteurization takes care of the rest, killing all of the enzymes that would aid in the digestion of this chemical monstrosity, putting the final cards in place to facilitate the transformation of milk from a benevolent Dr. Jekyll into a slavering, soul-rending, baby-raping, eviscerating horrorshow of a Mr. Hyde. At best, it's a quick way to get fat as shit, in my opinion, unless you swing a sledge all day long at work, or you've got the most freakish metabolism of all time, and at worst, you can pretty much wreck every one of your body's internal systems with GOMAD.