I found I stopped hitting walls and levelled out my pace a lot once I started running while fasted. I was doing IF for about two years while running 20-30km once per week or so, and I liked it quite a bit. Eventually I moved in with my girlfriend and her and her son found it too weird that I didn't eat with them - I'd just hang out while they ate the food I made. That's the big barrier with IF. Everyone wants you to eat, so I stopped doing IF consistently.

I had a similar experience with the social pressure around eating and fasting. I’ve had people get upset with me for doing a water fast and not joining them in eating while we’d sit around a dinner table. I workout a good amount (running, yoga, weights, swimming) and they thought I was being crazy, or they just felt judged for eating. For me it didn’t even register that highly: I’d wake up, decide to do it for a couple days to see what the effects on my body were, and that’s about it.

Honestly the hardest part was from other people, the fasting part was fairly easy and made me feel great.

Same - and I’ve recently upped my long runs to 12mi, which I do before eating anything. I’m sure there are limits where you need to fuel before or during an endurance activity, but I’m surprised and happy to not have found it yet.

I think we really over-estimate the degree to which "fasting" for less than one day affects our ability to perform. We're blessed with such an abundance of food in the west that few of us have ever felt real hunger. Your body is so far from hitting a wall after 12 hours of no food it doesn't seem to be anything but mental. I've done tons of fasted weight training and high-intensity cardio.

I grew up doing sunrise to sunset fasts for Ramadan, with no water, and even that was mostly mental.

Alternative perspective: after three hours without food during the day I begin physically shaking and have to fight an urge to curl up in a ball.

I can manage about seven hours sleep + a run first thing but I have to start eating as soon as I'm back in the house, and just keep grazing until 22:00

It would be a good idea to speak to a physician.

That's not because your current system has any problems--if it works for you, great! But that discomfort you describe is both abnormal and frequently linked to health issues that could cause serious problems over time.

Source: dietician relative on the couch next to me, FWIW.

You might want to get checked for hypoglycemia. That doesn't sound normal. (Unless you pair too much caffeine with your fasting)

The fact that you can do nighttime "fast" but get anxious after 3 hours while awake indicates it's just a mental issue as well.

Sounds like you have a serious medical problem, you should see a doctor.

You're an outlier.

I bonked out hard after going on a run after eating only a banana since waking up. Now I always make sure I've had at least a few hundred calories

That's because you ate that banana. That stimulated insulin release and your body couldn't use fat as energy.

Do you fast, though? If you're used to eating before exercise, there'll be a big psychological barrier.

my body does not work right out of bed. it takes me 30-45 minutes until I feel like I can make any exersion. if I force it I have zero energy. I don't eat first but I can't exercise right out of bed.