hmmmm, 600 ml is not bad and even 800ml if you are accustomed to it... you see, the digestion of milk involves an enzyme produced by the bacterial flora of the guts.... so if you had stopped taking milk , then there is a change in the flora of the guts and so there is decrease in the digestibility of the milk and its constituents... but if you are well accustomed to it, no problem because the body would have adopted itself to the digestion of milk....
but personally, 1.1-1.3L a day is too much>>>!!!!!