Wow, thanks for the responses guys. I've been experimenting with different types of carbs and I haven't had much luck :( Lots of low energy days followed by quick sugar fixes. I've been trying to follow a low-gi diet but for whatever reason it's not working for me. I definitely need to do more research on this.
I'm not sure if it's low-GI diets that are in question, I think it's the actual low (all) carb diets that, in theory, could affect mental performance as a result of low glucose levels.
Getting rid of high GI carbs could only help, in my opinion. You might be experiencing a few days of low energy immediately after dropping high GI carbs because your system is readjusting energy sources from quick, easily-digested bursts to a steady stream (of glucose). I guess it would make sense that, if you're used to a constant supply of quick energy carb fixes, dropping that could affect your overall mental performance for a few days, but it won't last long. Try staying on low GI carbs (while balancing fats and proteins appropriately, generally, less carbs=more fats) for a week and see if your mood/energy levels improve. I'd say they most likely will.
*EDIT - after reading RWAC's response, I realize I misread the question/your dietary experience. Anyway, I agree with RWAC. Any significant energy change is going to take some adjusting. I perform much better mentally and physically on less than 100 carbs a day (which isn't low carb by definition, but still much lower than I used to be) with high fats and somewhat higher than average SAD protein, and I have read many experiences here and elsewhere who have the same claim. Going from 250+ carbs/day to 50 takes some time, but could be well worth the transition period for you.
Edited by humanhibernaculum, 12 February 2010 - 03:19 PM.