Originally Posted by
canklecat
I don't ride on intermittent fasting days, or I eat a couple of hours before I do ride. I know from years of experience I'll bonk hard if I try to ride without eating. If I've gone 12-20 hours without eating and still want to ride or exercise, I'll have my usual pre-ride meal: oatmeal, banana and yogurt, with coffee. Works reliably for me.
But I doubt I have enough stored fat to test any theory on diet and exercise. It might work for folks with enough stored fat, no history of blood sugar problems, and other metabolic variables that make it work for them. Some anecdotes claim women are better suited to that sort of approach. I just know it doesn't work for me.
I do have a few pounds of fat around the middle and I'm so close to being optimally lean that I'm tempted to give it a try at paring down. Just for the challenge, no particular goal. But I'd need a much more methodical approach, and I'd need to decide whether I'm willing to sacrifice my few vices: a few beers a week; creamer in coffee, muffins with breakfast a few times a month (less than I used to eat), an occasional cookie or bit of chocolate hours away from any workout where those sugars and carbs won't be burned up.
So for now I'm depending on 2-3 hard rides a week at or near maximum sustainable effort, including one a week with HIIT. Seems to be working, which kinda reduces my motivation to sacrifice any more than I already have. I'd need to be persuaded that losing 2-5 lbs of fat would result in a significant improvement in my bike riding power and speed. But it won't. My primary obstacles are unrelated to weight -- mostly respiratory and a couple other pesky issues. Losing a couple or few pounds won't matter.
If you feel that you'll bonk if you ride without eating, it's because you don't try, but it's really very important for you to do so. Fat burning is a critical metabolic pathway to develop. That's kinda what this thread's about IMO. Humans have evolved to be really good at exercising without eating - just burning fat. You gotta get up in the morning and go out and hunt down something, then carry at least some of it back to your group. Or hunt for a few days without getting anything. That's all built in. But civilization blunts that ability.
So what you do is to go out without eating, but bring a waterbottle full of sports drink. Ride at a moderate pace. After about 1/2 hour, you might feel a bit hungry, even a bit woozy. Ignore it and keep riding. Maybe 10 minutes later, you'll start to feel better. Keep riding. Some time around maybe an hour, you'll start to feel weak. That's not bonking, it's just blood sugar dropping out because you're so bad at recruiting fatty acids from your plentiful deposits of same. So then drink a few swallows of the sports drink. You'll feel better. Keep riding. A while later you'll get really hungry. Time to suck on the bottle in earnest and head for home. You still won't bonk, but you'll get uncomfortable. Keep working at this and you'll gradually get better at it. In maybe a year, you'll be able to easily ride 2 hours or more on an empty stomach.
Anyway, this is the process one goes through to stimulate fat burning during exercise. Has to be done with exercise. Just sitting around and not eating isn't the same thing.
This is also how those with tendency for hypoglycemia, like I have, make that go mostly away and fixes our blood sugar issue.
Read through the links that I and redlude put up in our comments. Forcing your body to burn fat during exercise is definitely a way to get faster. So far, and AFAIK, fasting has nothing to do with it.
Even the slimmest marathoner has enough bodyfat to fuel at least 3 consecutive marathons.