Well, after reading what Vlad had to say, I decided to try switching to low carbs and high protein amd give it a try. This is based on only one day, of course, so it isn't anything definite or tested....
On the down side, I felt tired, cranky, and irritable (though I certainly didn't have any problem biking--the energy was there when I needed it.)
On the up side, I dropped 3 pounds overnight.
Guess I'll give it a few more days testing....