This is a subject that is near and dear to my heart as I lost weight doing a low-carb, higher protein plan (primarily based on the Eades' book Protein Power) a couple of years ago. I only had 15 lbs. to lose, which doesn't seem like much, but on my 5'2" frame made a difference - I went down two sizes.I weight trained and did lots of walking during the weight loss and never had a problem with that level of activity on low carb. About the time I finished losing the weight, I started cycling again - this was fall of 2002.
What I found was that I did have to up the carbs to do longer rides (anything > 20 miles), and I also have found that over time I have put a few lbs. back on (just 3-4). The good news is that my new clothes still fit me and I am a stronger cyclist, so I think that most of it is muscle, though I know I'm carrying a bit more flab around the waistline/hips than at my lowest weight. However, I also have a lot more energy, so I can put up with that. At 43, I am not going to have the total hardbody of an 18-year old no matter how much I ride and work out, and I just have to accept that.
All that said, what I do is not worry about carbs on long ride days. I eat plenty of 'em before, during, and after rides. Ride to eat!I often find that my weight inches up 2 lbs. over a weekend, when I ride the most, so during the week, when my rides are shorter, I cut back on carbs to some extent. I don't cut back on veggies but avoid white carbs, potatoes, and sugar. The 2 lbs gained, which I think is caused by the water that carbs cause me to retain, drops off easily during the week, only to return again after the weekend!
I think the key is to favor complex carbs like whole grains, vegetables, and fruits, and try to avoid the "empty" white carbs like white bread, sugar, white rice, etc. unless you're doing a long ride, in which case you can probably indulge without gaining. But perhaps not - you may be one of the people who has to be careful despite a busy riding schedule. It can be hard to get adequate calories/carbs to ride well without going overboard, and I still work on that balance. I think Barry Sears' Zone plan is a good one that can be used by athletes, since it emphasizes a balance of carbs/protein/fat rather than cutting out one group completely. But right now I don't follow any specific plan; I just try to eat healthfully 95% of the time and splurge the other 5%!
I also cut back on carbs some still over the winter so I don't gain weight. I do Spinervals tapes on the trainer, but it's not the same as the long rides I do on the roads during the season (~150 miles per week).
Good luck!
Emily
P.S. Why does everyone want to spell Atkins, Adkins? I see this everywhere!