I don't know if anyone else has already thought of this and posted it, but just thought I'd tell you about my new theory.
Well, L eats tons of sugary food, but never gets hyperactive from a sugar rush or anything. He's pretty much always calm and such...
So I think L's body works differently than most of us. He doesn't become hyper from sugary foods, but he does become hyper from savoury foods, salty in particular.
So if L eats salt, he becomes very hyperactive. Which is why we don't actually see him eating savouries in the anime or manga (I've heard he eats crisps in the live action movie, but I haven't seen that yet...), because he'd behave like a lunatic.
What do you think?
This is not just a waffle. This is a flattened waffle. Osaka's pancake if you wish.