I normally eat 5 to 6 meals a day. I can't say I've replaced a meal with a shake though. However depending on the shake you take, yes, I believe that could be a meal replacement or supplement to a small meal. I however would ensure that I'm eating at least 3 to 4 meals of actual food. Also you don't want to over do your protein intact. Determine what you need for the day and then divide it amongst the meals with probably more for the meals where you know you will be active. I have no scientific back up but I'm hoping others will.
"IF I COME ... I'M BRINGING THE PAIN WITH ME"