There might be a gender difference for IF, how effective and the duration of the fast, and maybe also for the issue regarding breakfast.

I'd actually like to see a study done on IF and digestive health. The caveat with sedentary people is that IF is very difficult unless a specific diet is in place. That diet doesn't have to be Paleo and it doesn't even have to include "quality" food. However, those relying on glucose burning are going to find it difficult to even be quality test subjects for IF.

With that said, the biggest benefits I've seen from IF have been digestive health. For someone without fat to lose, I've noticed that the more consistently I incorporate IF, the better I'm able to handle "tougher to digest" foods. It has actually been a very beneficial system that has allowed me to easily transition from a very easily digestible diet to becoming very "flexible" in digestion. I can't help but think there is a clear correlation between digestive flexibility and metabolic flexibility, which is generally a benefit seen by those who IF.

This is what I'm studying though, more toward the digestive end of things, so it's definitely what I would lean toward.

You're obviously after a more scientific bent, but I'd like a sociological/anthropological analysis on what happens in your social life after you begin IF:

"You didn't eat breakfast? Isn't that like awful for your metabolism?" "Oh my gosh, how can you eat so much meat in one meal?" "You're so skinny but you eat a lot. Do you have like a really high metabolism or something?" "You must have thyroid issues."

In seriousness though, a study on satiety may be just as interesting: What leads to greater food satisfaction throughout the day? Insulin-resistant and breakfast eating or fat-adapted and fasting? I feel like the answer may be obvious based off of Martin's previous post, but then again we as a community tend to ignore any conventionally accepted wisdom. Clearly, lots of people are doing the 6 meals a day and loving it.

Twenty years ago (even more than that, make it 25) in the era when books like Fit for Life, Paleolithic Prescription, early Atkins, and others were coming out, I was a marathon runner, triathlon and other endurance competition racer. I could not handle eating breakfast, it made me more anxious, worse still with caffeine or any sugar, and I felt like a hot rock burning in my stomach. Also, toward the end of the race if I was hydrating with sweetened drinks I would start to feel depressed. Believing (correctly, I am still convinced) that the hypoglycemia is only a sequel to hyperglycemia, that all this leads to increased cortisol and then catabolism, and encouraged by those books, I switched to no breakfast (don't tell your mother) and would only drink before and during the races an herbal tea with a good dose of powdered ginger.

I continued to go without breakfast since. Once adapted, it took only a day or two with an apple instead of breakfast, I was happy to find my mood very steady and stable throughout the day. If I was occupied with some chore or in a race I never felt hungry at lunch time unless I did eat breakfast. Even a low body fat person has enough energy stored in that form to go many days without eating even if you are exercising. You need to develop you body's ability to mobilize fat.

I believe that is the result of low carb diet adaptation. You do not wake in the morning feeling hungry except initially or as a habit when the environment reminds you. It was (still is) a tremendous feeling of power and freedom to skip a meal without any ill effects, psychological or physical.

This also agrees with my experience doing fasts as long as 5 days. After 24 hours it is hunger free and painless. You feel empowered and invested and then the main problem is to stop fasting and start to eat. Take lots of psyllium mixed with water during the fast to keep your GALT in operation.

Based on that experience I guess that having your eating window in the morning would be much more difficult. Think about traditional religious fasts, usually dawn to dusk.

Weren't our paleolithic ancestors and their species typical diet based on evening feeding?