[Rhonda]: Another sort of question that sort of relates to this is, and people ask this
all the time, is what about people that are...start eating later in the day?
For example they wake up 8:00 in the morning, but they don't eat until noon.
So let's say they eat their first bite of food at noon, and they stop eating at 8:00
p.m.
So that's an 8:00 TRE eating window.
And they go to bed by 11:00 or so.
Do they still have the same benefits or are they losing because it's like the time-restricted
eating window has kind of shifted to later and obviously there is a light/darkness component
to all this to some degree?
[Satchin]: Yeah, yeah.
So those questions we haven't even teased them in animal models, but I'm sure some people
will start teasing them apart.
So what happens is in the morning we know insulin sensitivity is at its best.
So people who have a bigger meal earlier in the day, they have less insulin spike, less
glucose spike, etc.
Having said that, we don't know for people who are starting their food every day at noon
whether they're best insulin sensitivity is at noon or it actually happens at 8:00 in
the morning.
So that information we don't know.
So this is where some studies need human volunteers who are doing this.
And maybe some people who are doing...who are starting to eat at noon, one day maybe
they can drink a glass of juice at 8:00 and prick themselves and get a glucose reading
and monitor themselves.
And then another day, a week later at noon, they will eat the same glass of juice and
prick themselves and see how is their glucose response.
So that's a simple self-experimentation with some healthy people.
If they're out there, then they can do that.
And if they post it, that will be really nice.
Second thing is what happens toward the end of the day at night.
So this is where it becomes a little bit complicated because, as you said, there is day and night
transition.
And we know that in the evening as our body prepares to sleep, our melatonin level begins
to rise.
And that melatonin usually rises two to three hours before our habitual sleep time.
So if somebody is going to bed around 11:00, then that melatonin is beginning to rise around
9:00.
On an average, but some people it might rise around four hours early and some people it
will rise exactly at bedtime.
And when melatonin rises, there is new data showing that melatonin can bind to its receptor
in the pancreas.
And this engagement of melatonin with the pancreas receptor essentially tells the pancreas,
"Okay, it's time to sleep, you don't have to bother releasing insulin."
So in that way what happens if somebody is having a big meal when there's high melatonin,
then there may not be enough insulin to release from the pancreas and glucose may stay high
in the blood circulation for a long time.
And this study...these kind of studies came to publication because almost 10 years ago
large genome-wide association studies found that people with obesity or diabetes might
have a mutation in melatonin receptor.
And that was confusing because what has melatonin to do with obesity and diabetes?
And you fast-forward 10 years, people went back to the drawing board and looked at where
the receptor is expressed and what it does when melatonin is engaged, and then they found
out that there is this effect of melatonin on insulin.
So that's why people who are eating late into the night, they may not get the best benefit
in terms of glucose control because their glucose might remain slightly higher than
if they had the same dinner two hours earlier.
[Rhonda]: If they're making more melatonin.
[Satchin]: If they're making melatonin.
So it's very...so that's why I said it's complicated.
[Rhonda]: Yeah.
[Satchin]: But at the same time I would say eating randomly over 12 hours, 15 hours, versus
eating to this 8 hours, even though it starts at noon, I will prefer the 8 hours starting
at noon.
[Rhonda]: Right.
So it seems like there's, in addition to, you know, the timing of your food intake,
so we know the first time you're eating sort of starts a lot of these liver enzymes and
metabolism...glucose metabolism and all these things.
In addition to that, that circadian rhythm being regulated by just the food intake, there's
also this whole melatonin issue and the night-daylight cycle and, you know, when you're starting
to make more melatonin.
And all that complicates things, as well.
[Satchin]: Yeah.
[Rhonda]: It seems.
Yeah, I remember a study that was done where I think men were given the same caloric meal
in the morning and the evening.
[Satchin]: Yeah.
[Rhonda]: And glucose was measured and the blood glucose levels were much higher in the
evening versus morning.
But, of course, they could have been.
Who knows how long...
You know, was the morning, like, 8:00 a.m. , and then they were doing, you know, 9:00
p.m.or 8:00?
So who knows what their timing window was, right?
[Satchin]: The habitual meal, what is their habitual meal?
[Rhonda]: Right.
[Satchin]: That's a very widely observed phenomenon.
In fact, there was a term for that that was called evening diabetes.
So a person might be healthy in the morning based on blood glucose.
In the evening if you do the same postprandial glucose tolerance test and then look at the
glucose level, then maybe diagnosed diabetic.
[Rhonda]: Right, right, yeah.
[Satchin]: Yeah.
[Rhonda]: Well, I think the other component to this would be the fasting component, right?
So people think, "Well, I'm only eating within an eight-hour window, so I have a much longer
fasting period."
And I think that's maybe uncoupling some of these differences between time-restricted
eating, being on a circadian rhythm, and fasting, intermittent fasting, prolonged fasting.
You know, there's so many different terms out there.
[Satchin]: Yeah.
[Rhonda]: And I think sometimes a lot of it just all gets mushed together in one group
and it's, like, all the same.
[Satchin]: Yeah.
[Rhonda]: But it's not actually all the same.
[Satchin]: No, it's not the same.
So, for example, even not having food in your system for 12 to 16 hours, whether it's fasting
or not, that's debatable.
Because some people say, "Well, it's not fasting, it's not having food for 12 hours."
And I think that's where I would say not having food for 12 to 16 hours is not fasting, but
maybe giving rest to your system, rest and repair and rejuvenation of your system.
So when we think about fasting, or when you think about fasting, two things come to mind.
Feeling hungry.
And feeling hungry has many different connotations, many different intensity.
So one sense of feeling hungry is, well, you might feel light.
And then second, your stomach may begin to frump a little bit.
And then I always say that is your stomach is telling you, "Well, I'm repairing myself."
You're not actually really hungry, you're not getting low energy that you cannot get
up from the chair or run or something like that.
And then after several, maybe one or two, days of fasting, or maybe after 24 hours of
fasting, some people will get a head ache.
So that's a good sign that, well, your brain is not getting enough energy in its habitual
usual form and may be trying to signal the rest of the body that the body has to send
some other form of energy, for example ketone bodies or something.
So in that way fasting, if you're measuring fasting or you're defining fasting in terms
of ketone body formation above a certain level, then that may kick in after 24 hours.
Or if you have that threshold even much higher than fasting, maybe 20, 48, or 72, or even
96 hours before you see that level of ketone bodies that can be your definition of fasting.
So in that way I think the way you define fasting will determine whether 24 hours, 48
hours, 96 hours, or even 12 hours or 16 hours is fasting.
But the way we think, we kind of define how many hours your system should not have food
is based on our daily circadian rhythm.
Because if you think about what are the key elements to being healthy, it boils down to
three important things.
One is sleep, and the second one is nutritional food, and the third one is physical activity.
And these three are interlinked with each other.
So, for example, if somebody is sleep deprived or didn't have sleep, then it's very hard
for that person to do physical activity the next day or go on a marathon.
So these two are interlinked.
Similarly, if somebody is eating for 15, 16 hours and has a very heavy meal at the end
of the day, then it affects sleep.
It also affects physical activity.
One cannot run with a full stomach.
So these three are interrelated.
So on a daily basis what we feel is having...limiting food to 8 to 10, or maximum 12, hours helps
to coordinate these three foundations of health to work on a daily basis and give us healthy
benefit.
So on a very simple sense if I want to relate time-restricted eating and then maybe long-term
fasting, one day of fasting, two days of fasting, or four days of fasting, which definitely
have much more benefit, then it's almost like taking care of your teeth.
So brushing every day is like time-restricted eating.
There's the minimum one can do and that's something necessary to take care of your teeth.
But, again, once in a while, maybe twice a year or three times a year or once a year,
depending on how much you want to take care of your teeth, you want to go see a dentist.
So that's almost like a prolonged fast one has to do once a year.
So similarly I do four to five days of water fasting only once a year and that absolves
all the other sins with my feeding that I might have committed throughout the year.
So in that way I think the difference between time-restricted eating and other forms of
fasting is one can adopt time-restricted eating as a true lifestyle, starting even from teenage
or even toddler years, all the way through when you are 80s, 90s, or even 100 years old.
Whereas this long-term fasting, two days or four days of fasting, forget about even teenagers
doing it.
And some older people who are very fragile, they might not be able to do it.
And you need medical intervention or some kind of supervision to do it.
Many people who are slightly unhealthy, even some diabetics who might go hypoglycemic after
10, 12 hours, type II diabetic I mean, they may not be able to do it without medical supervision.
So although those long-term fasting definitely have much benefit, and that has been shown
in multiple studies, the need is that they can be practiced only by a certain type of
people at certain days and need more mental resolve.
And it may not be an everyday lifestyle, whereas time-restricted eating can be an everyday
lifestyle.
[Rhonda]: That's a great way of putting it.