I try to watch my carbs and not eat a bunch of junk food like ice cream and chips but low carb options really won't replace something like goo because it is pretty much pure carbs. I hear bananas and raisins are nearly as good as goo but definitely not low carb. =)
Carbs are critical for any running....esspecially long distance runners. I can't imagine trying to run more than 6 miles without carbs. Try (as KaelynsMana mentioned) bananas, which are also a great source of potassium.
When I first started C25k, I was following Atkins. I also did the program 6 days a week instead of 3. By week 3 I was noticing that I was tired all the time. Week 4, I was napping 3-4 hours a day (after my runs) on top of 8-10 hours of sleep at night. Even with all that sleeping, I was still exhausted all the time. Soon, I was suffering from fatigue. A friend of mine told me that low carb diets are for people who don't exercise and that I needed to add complex carbs to my diet.. best piece of advice ever. I started eating brown rice, wheat bread, whole wheat pasta, etc, I'm still losing weight, but I'm no longer fatigued.