Hi Donna,
The theory is your background insulin (Lantus) should hold your BG steady for 24 hours assuming you aren't eating, exercising or taking quick acting insulin to influence blood glucose another way.
Carb free meals can actually be a useful tool. I've recently been trying a few (albeit reluctantly!) to check whether I'm getting my background insulin right.
The fast acting insulin is the tool to bring your blood glucose back down after carbs.
I started running last year, and take a lot less quick acting insulin before going out to do it, because I know the running will drop my blood glucose a lot.
Just be aware that changes to your Lantus should ideally be done gradually: it seems to take about 3 days before the effects of reducing Lantus becomes noticable!
If you don't want to eat as many carbs there really is no need to, and when you'd rather have more carbs that's what the rapid stuff is for.
Hope this helps.