My first realization that this was perhaps flawed logic came when I was chatting with a co-worker about our newly-acquired Greek Tortoise and his Iguana (or some reptile). He mentioned that I need to stay away from Iceberg Lettuce, to which I responded, "Really?" With a horrified look on his face he began to explain how bad Iceberg is for reptiles! Unfortunately, we had just purchased a big bag of this lettuce because it was so cheap and Samson (our Greek Tortoise) seemed to like it. After I gave my wife the bad news we began our continuing journey to find the perfect diet for our Greek Tortoises.
While my co-worker's concern was understandable, his information was not accurate. Iceberg Lettuce isn't any worse for reptiles than it is for humans. On the other hand, it isn't any better for humans than it is for reptiles. Iceberg is full of water, but it's severely lacking on the nutrient side of things. Therefore, a diet based solely on Iceberg will eventually cause numerous health problems.
In fact, a diet lacking in variety (regardless of what food is abundant) will eventually cause any number of health problems simply due to the fact that no one food fills all of the nutrient requirements of Greek Tortoises.
This is a subject that I will frequently revisit.