So there is a famous experiment that was published last year by Joe Takahashi's lab, and it came out in Science, and that relates to caloric restriction. And we kind of started with this idea, we started discussing that the rat experiments were done with caloric restriction, and researchers gave reduced calorie consumption by 20 percent or 30 percent and gave that food, the rats, and then subsequently mice, and they all lived longer.

What is interesting is, in all those experiments, the researchers came and gave this bolus of food at one time, whereas the ad libitum fed mice or rats, they had access to food all the time. So they were eating all the time, and then these rats were given 20 percent less.

And what happens is, these mice or rats, they're not going to take that less food, which is rationed now, and just eat a little bit of lunch and then snack after three hours or snack after three hours. They gobble up all that food. Within two to three hours, maximum four hours, food is gone.

So they're sort of on the OMAD diet, the one meal a day. Yeah. They're almost like in one meal a day, three to four hours, food is gone. Or you can say they're on four hours eating or feeding and 20 hours fasting. So then the question became, well, the benefit of caloric restriction, as we know, is it due to reduced calorie or time-restricted feeding?

There is a timing component to it, that they're eating all of that within three to four hours, and then there is a long fasting. And this is a difficult question to answer, because now you have to ask these poor grad students or technicians to come and split that food into eight or 10 or 15 different small portions and then give them to mice in every two hours.

So Joe Takahashi, who actually published the first paper in 2017 showing that most caloric restrictions, I mean, he used the protocol that was used by caloric restriction field, it actually creates a condition of time restriction. So he showed that, and then he went back and worked with engineers to come up with a smart case where he could actually tell, he could program how much food is given to mice at what time of the day or night, completely programmed.

So then he took this, for example, let's say the ad libitum fed mice eats five grams of chow in a day. And if you want to reduce calories by 20%, then the CR mouse should get four grams of food. And he divided this into nine or 10 meals, and then gave them in every 90 minutes.

So in this case, they are eating small meals throughout day and night, so there is no fasting. So you can say that, well, this mouse actually is not getting into fasting because in every few hours is getting some food. And then he measured how long the mouse is going to live.

And he used account, means this is a very standard protocol, people count how many mice are dying on which day and then examine them to see whether they died because there was an accident or they actually, there was a natural cause. And then they calculate at the end, what is the half life?

So 50% survival, because that's on an average, that's a good indicator because if there is an outlier that will live for a long time, then that can skew. So what was interesting was the ad libitum fed mice, of course, they live certain number of days, and then this caloric restricted mice that never got into super fasting, but kind of eating, snacking throughout day and night, that also lived 10% extra, 10% longer.

So that means caloric restriction extended lifespan by 10%. - I've wondered about this because recently, you know, there's been, there were a bunch of news headlines about intermittent fasting. And frankly, I was frustrated if you looked at one major news outlet, they would say time restricted feeding affords no additional benefit beyond caloric restriction for weight loss.

Then another popular press venue, let's call it that, same study described as time restricted feeding doesn't work. Right. And then another one, maybe someplace even more extreme, you know, time restricted feeding only beneficial because of caloric restriction or something like that. So what you've essentially got are three different interpretations of the same data, all of which are, well, two of which are true, one of which is false in my opinion.

But what I think people take away from that is, oh, time restricted feeding isn't valuable, which is not the case. I think for many people, it's a convenient way to eat because at least for people like me, it's simpler to designate between portions of my day when I'm eating and portions of my day when I'm not eating, as opposed to portion control.

For other people, portion control can work. But all of that is related to either maintenance or loss of weight. None of it deals with the potential health benefits independent of weight loss. And so I think that if we can segment those out, obviously in humans, it's hard to know if a given treatment or experiment is extending life because you don't really know how long people would live anyway.

Right. Whereas with mice, you have some sense of when the mortality was likely to occur. So what can we say about time restricted feeding and longevity in terms of biomarkers or in terms of any other indication that people who start and stop their feeding window at a consistent time, somewhere between eight and 12 hours per 24-hour cycle, are tilting the scales towards living longer as opposed to living shorter?

This example of this news article that you mentioned is really interesting because that relates to Joe Takahashi's study, because I described that if you split calories and eat throughout the day, throughout day and night, then the mice live 10% extra. But if you now give mouse the same calorie restricted diet and feed them during daytime, whether within 12 hours or two hours, then the mice live 10% extra.

Beyond that? Yeah. So 20% longer. 20%. So, okay. So let me make sure I understand so that I make sure I understand. If you take a certain number of calories and you distribute them throughout the 24-hour cycle, it's caloric restriction, the mice will live 10% longer. If you, however, restrict that to the active cycle, so for humans, the daytime, then they live 20% longer.

20% longer. So it's not just total caloric intake, meaning it's not just important to be sub-maintenance in calories for sake of longevity. It also is important as to when in the 24-hour cycle you eat those calories. Do I have that right? So now, that's still, the story is not over because these mice are fed during daytime when they're not supposed to eat.

That's right. So for us, it would be the equivalent of being on the night shift and only eating at night, but a sub-caloric, sub-maintenance calorie diet, I guess is the right way to say it. But when you fed mice during nighttime when they're supposed to eat and they're getting the same number of calories within 12 hours or two hours, then the mice live 35% longer than they control.

35% longer. So scale to human lifespan, which we don't know, but 35% longer would mean that, and again, no one knows, but humans now, what is the average mortality in the United States, somewhere around 80? Yeah, so it's around 80. It used to be 80, now it's reduced a little bit because of COVID, but let's take 80.

Okay, so people are then now living somewhere between 25 and 35 years longer. I'm putting some error bars on that. Yeah, yeah, yeah. Amazing. So that was really profound, but now you pointed out biomarker and other stuff. So now, if you look at any given time within that experiment, and actually Joe went back and had a separate cohort of mice, very similar, and so that he could take tissue samples.

And of course, in this case, you have to sacrifice the mouse. And he looked for, he did a lot of molecular analysis with known markers, for example, hemoglobin A1C equivalent, or glucose control, cholesterol, all this stuff. He could not find anything that predicted the benefit of caloric restriction. So that means in this experiment, whatever we know so far, the predictor of longevity, none of them could predict whether this CR only mouse, which ate throughout day and night, that mouse is going to live less than the night fed mouse that was going to live 25% extra.

Does that mean that there are biomarkers related to longevity that we just haven't discovered yet? Yeah, so that's exactly. So that means whatever we know so far about biomarkers, he could not use to predict. Maybe there was a lot of noise, maybe he had to use more number of mice to get that, because biomarkers are not going to predict in every instance that there is some error.

What is also very interesting is, if you look at the body weight and body composition of all these mice, there is no difference in body weight and body composition. Across all these different groups? Across all these groups. So it doesn't matter when they ate, provided they were sub-maintenance calorie intake, fewer calories than is required to maintain their weight, didn't matter what pattern of eating, they were the same weight.

So that in many ways seems to mimic the human studies where they say, "Look, it doesn't really matter whether or not you use caloric restriction, or you start your feeding window in the morning, or start your feeding window in the evening, or you portion control for sake of weight loss." Because they're taking a snapshot of that.

And then another thing with the human study that we are referring to here, in that human study, people are actually already eating within 10 hours window, habitually, when they selected these people to have them enroll in the study. So they were already eating for 10 hours and fasting for 14 hours.

All participants had to reduce their caloric intake, and they reduced by almost 25%. The CR group continued with 10 hour sitting window, and the CR plus time-restricted group had to eat the same number of calories within eight hours. - So it's just a two-hour difference. - It's just a two hours difference.

- Okay, so that people, I just want to make sure people can understand. So in this human study, which is the one that I felt that the popular press venues, all except one venue, got either semi-wrong or badly wrong in terms of their conclusion. That was my interpretation anyway, was that either people came into the study eating basically in a 10 hour feeding window, which goes back to my first question, which is that most people are not eating in the middle of the night, or if they're on shift work and they are, then they're sleeping during the day anyway.

So they're eating in a 10 to 12 hour feeding window anyway. So you're saying they either did caloric restriction, portion control within the 10 hour window, or another group within the study ate sub-maintenance calories. So caloric restriction, CR, as we're calling it, the acronym CR, but restricted that to an eight hour feeding window.

And they didn't see any difference in terms of weight loss. But it's not all that surprising, right? I mean, if it's just a two hour difference. - Yeah, exactly. So we have done that experiment in mice and we don't see difference in not only weight loss, many other markers.

And I was telling you about this Joe Takahashi's paper where I told you that he allowed these mice to eat within two hours or 12 hours, sub-caloric diet. - Two or 12? - Two or 12. - Yeah, that's dramatic. - But still, he did not see change in longevity even within those two.

So that means when you do caloric restriction and then at least for mouse, and you are within 12 hours window, that is giving the mice the best benefit, the optimum benefit. And two, three, or five or 12 for a mouse doesn't matter, at least for longevity.