Optimal, I guess in terms of weight loss. But steady energy throughout the day would be important, too. I eat VLC, so please answer keeping that in mind.
From a evolutionary perspective, my guess is that most hunting would be done during the day and therefore food would have been eaten most often in the evening.
If you are exercising, I would recommend eating your meal post workout to help refuel your body.
If not, I would just eat when hungry. Most people tend to be hungry later in the day rather than in the morning.
I try to do 1-2 24-hour IFs per week. I've found that eating my single meal around 4-6 pm works best for me; earlier than that, and I might enter the fasting state before I fall asleep at night, which can often lead to insomnia for me; later than that, and I don't feel the same fat-burning benefits if I go to sleep on a full stomach...
We have this built in mechanism called hunger. Make use of it. But beware that sugar or large amounts of carbs, or working out too much, can throw it into overdrive. And beware of boredom which can trigger eating as entertainment.
If you stick to fat/protein, hunger works very nicely as the proper stimulus to eat. If you're not hungry, don't eat. Simple as that. We don't have to eat on schedule, that idea is silly, unless you're doing something like a leptin reset.
Cravings also tell you what nutrients you need - or give you hints. (Unless you're craving junk, in which case, try to find out what you need and substitute.)
I have a history of GERD (much, much better with ancestral eating) so it's not a good idea for me to eat within 4-5 hours of bedtime.
As raydawg mentioned, it's best to wait for hunger but that's usually mid-to-late morning or about 2 hours after exercise so my meal is fairly early unless schedule prevents me from eating until later. If it's too late, I just wait until the next day to avoid GERD.
I would do it post workout, whenever that is. Lately, I've been really busy at work and haven't been eating lunch, which means by the time I get to my workout after work, I'm deep in ketosis. I've actually had better workouts lately. Even on the timed metcons, I don't feel like I'm moving as fast, but I'm also never stopping to take breaks. I'm usually #3-#5 in our gym on a heavy metcon workout, but last week I was #1 or #2 all week, which is pretty hard because I can't normally beat the 20 year olds. The only change I've made is that I'm not working out fasted (11 hours since breakfast). So I don't see any issue with putting your meal after the biggest energy expenditure you have for the day.
Though, I am against planned fasting, or fasting for fastings sake. If you're hungry eat!
As other people have said, eat when you're hungry, that's your body's way of telling you you need calories and nutrients. I think you're probably right about what our ancestors did since it's not likely they had piles of food waiting for them when they woke up in the morning like us, although possible.
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