If you trot on over to Paleo/Primal communities, there are a lot of athletes who subsist on lower carb plans. It's entirely doable, but I'm sure depends on the amount of exercise one is doing. Running/training for a marathon surely involves different nutritional needs than most people's workout routines.
I eat a lower-carb diet most of the time. Not intentionally, it's just where I gravitate. Now I don't go as low as traditional low carb plans; I tend to eat around 100-150g of carbs a day, with just about all of it coming from fruits and starchy veggies. I find my exercise is fine. In fact, before I lift heavy I often eat almost no carbs and my lifts are fine...the only time I have trouble is when I haven't gotten enough sleep!
Like
CabernetKitty, I have eggs in the morning before my workouts.
Of course, with anything, YMMV. Everyone has different nutritional needs and find different things work for them.