one point that you just mentioned is important.
And this can occasionally get lost as these conversations go on.
And that is, it's the switching back and forth intermittently, is important.
For example, in the muscle cells with exercise, the number of mitochondria
doesn't increase during the exercise, it increases during the rest period.
But if you had never exercised, you would have never gotten a stimulus that triggers
what's called mitochondrial biogenesis, the increase the number of mitochondria.
So, the switching back and forth between the metabolic challenge,
whether it's fasting or exercise, and the recovery, well, you know,
eating, resting, sleeping, you know.
And there's definitely a limit to all of this.
Obviously, with fasting, starvation.
You know, if you start to lose muscle mass, then you're fasting too much.
And, as you mentioned, you can overdo it with exercise too and
sometimes get diminishing returns.
So, it's important to have these recovery periods.
You've talked about the importance of what are called the refeeding phase.
Both, you know, you and Dr.
Valter Longo have discussed this in publications and Valter
on the podcast previously.
Like you mentioned, it's a point that a lot of, you know, people
don't focus on that recovery period.
For the refeeding period, you know, how important is that?
And how long is that window?
Do we know?
You know, is it like a week?
Is it just a couple of days?
Well, with these intermittent fasting eating patterns I'm
talking about are kind of trivial from an evolutionary perspective.
That is limiting time window you eat six to eight hours each day.
You know, the remaining, whatever, 16 to 18 hours is
more than sufficient to recover.
If you fasted or if you tried to do fasting for five days, one day
recovery, fast another five days, one day recovery, and keep that up.
It won't be long before you're going to start to have problems.
So, it's the same with exercise.
You know, my understanding is there's quite a few ultra marathoners who,
when they get in their 50s and 60s started to have a lot of problems.
So, you know, there could be some long-term consequences of overdoing it,
whether it's with fasting or exercise.
And what you and I are talking about today is well within any bounds of even getting
close to having adverse effects and having to worry about, "Am I recovering or not?"
But perhaps more of someone doing more of a prolonged fast might
have to consider, you know, the refeeding and how important, I know...
In Europe, for example, in Germany, there are clinics where people
go in for a couple of weeks and they'll fast for 10 days to 2 weeks
and they're, you know, supervised.
It's kind of like a resort, actually, you know.
And everybody else there is doing the same thing.
And they're collecting a lot of data and starting to publish.
They see a lot of improvements in health indicators even within that,
you know, two-week fasting period.
But they don't have really good data on long-term effects.
And in talking to the people who run these centers, oftentimes, a
person will only do this once a year.
And so, they may be overweight and, you know, have insulin resistance.
And they'll go in, and they'll show some, even during that short
period, a little bit of improvement in their insulin sensitivity.
But then, they'll come back a year later.
And they're back where they were or worse.
So, you know, one question then is if someone wants to fast for longer
time periods, what frequency would be reasonable for long-term health?
You've interviewed Valter Longo before, and he's done a lot of work with this
eating pattern where the subjects, five consecutive days a month, they'll
eat only one moderate-sized meal.
And then, the other days of the month, eat normally.
And that seems to be beneficial.
The key thing is, you know, how long can people maintain this in their lifestyle,
incorporate it in their lifestyle?
Daily time-restricted eating, for example, seems to be easy for a lot of people
to do for years and years and years.
You know, maybe five days a month, that's perhaps...
But at some point, you have to think about it that way, looking kind
of a long view of what can you...?
And then, another thing is, what about...?
You know, so daily time-restricted eating, if you skip breakfast, then
you can still have lunch with people at work and dinner with people.
Where, if you're doing something else, maybe, like Valter's maybe five days a
month, you're not going to be able to...
You may go out to dinner with somebody and say, "Well, I can't eat anything today."
Yeah.
Right.