Carrie,
dont panic as a one off, we have all (maybe) done it.
But dont do it on a regular basis.
The shakes give you the minimum you need for a days nutrition. Below that your body goes into starvation mode which means it conserve even the most meagre of calories. Even LT!! When you come off LT your body will again conserve! So for the best effect take your 3 shakes a day and drink at least 2l of fluids on top of your shakes!!
Good luck!!