The fact that you are concerned about it is probably a help. Before you worry too much I'd considered the reasons you are using shakes instead of food, and whether those are good or bad reasons.

I often eat an Atkins bar or shake in place of a meal, because my job is often hectic and there's not a lot of variety at the cafeteria. And frankly I'd rather sleep five extra minutes in the morning!

But it didn't interfere with my weight loss or my maintenance. That's the bottom line.