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The downside to training fasted is something along the lines of:
Training fueled means you perform at a higher level than if you were fasted/not-fueled. So, if you don't ride as hard, you don't adapt to a higher training intensity, you're not getting as fast.Also, some evidence that training fueled, especially in longer stuff, helps avoid colds and other ailments because less cortisol (stress hormone) is produced when fed vs. fasted.
Why would you not push too hard when training fasted...especially if you're only doing up to an hour or so? I do virtually all my training first thing in the morning, and then cycle to work before having breakfast! Would it not also be the case that training in the morning after having had a decent dinner the night before isn't quite the same as training fasted?
TL;DR I've no answers for you, only questions!