I've never heard that eggplant isn't nutritious...and it's not true. A quick google shows that it's "a good source of Vitamin K, Thiamin, Vitamin B6, Folate, Potassium and Manganese, and a very good source of Dietary Fiber." But it is high in Sodium.
http://nutritiondata.self.com/facts/vegetables-and-vegetable-products/2858/2

I dunno why people say this about various fruits and vegetable. Even iceberg lettuce isn't completely void of nutrition. There are just sometimes better options when it comes to nutrition. Of course, I'm not going to replace eggplant with brussel sprouts. I like eggplant. I can't say the same about the unholy green gremlins. :P