The way I conceptualize the idea of fasting, obviously this is one where we need more words, right? Because the word fasting is so limited, there's so many different parts of this, but… Skipping breakfast for me would be that, or skipping dinner. Right. Sometimes I'll skip dinner, sometimes I'll skip breakfast.

Right. I think that some of the most interesting data that I've seen has been about if we reasonably compress our eating into daytime hours during the part of the diurnal cycle when we are supposed to be eating. So essentially matching our chronobiology with our behavior, which, you know, we are diurnal organisms, so we kind of need to respect that.

Like when we do that and we compress it in a moderate way, our metabolic health is better. And so some of the studies that have looked at this, one that was interesting was, and I think very hopeful for people, is that if you take all the food, all the calories that you're going to eat, and eat them in a 6-hour window versus a 12-hour window, totally same amount of calories, exact same food.

This is a controlled experiment. People who eat the same amount of calories in a 6-hour period are going to have much lower, statistically significantly lower, glucose, 24-hour glucose and insulin levels compared to people who just space it out over the course of a 12-hour period. And it makes sense because if you're spacing that food out over the course of 12 hours, that is a different biochemical milieu in your body throughout the day.

It's kind of similar to the walking. You know, it's like you are then stimulating insulin several more times. You are exposing the bloodstream to insulin and glucose just more throughout the day. And giving the bloodstream less of an opportunity to just sort of be clear from that glucose and that insulin.

And so compressing our eating window seems to be helpful for metabolic health. And it's a bang for your buck, right? Like you can eat the same amount of food. You just have to eat in a shorter period of time. So for people who want to eat, you know, a lot, maybe just consider compressing it into daytime hours, 6- to 8-hour window.

Yeah. For me, 6 is tough. 6 is tough, yeah. The one meal per day thing is tough. I have friends like Lex Freedman that do the one meal per day thing. I end up eating so much food at that meal that I experience a lot of kind of like mechanical distress as typically later in the day.

I think an 8- to 10-hour window has worked well for me most days. I know as soon as we talk about intermittent fasting, which is what, or time-restricted feeding, same thing, which is what we're talking about right now, I'm sure somebody is going to call up the, there's been a study that's been circulating about a massive increase in cardiovascular risk in people doing intermittent fasting and particularly the 6-hour feeding window.

I just want to point out. Worst study. As far as I know, I could be wrong, but as far as I know, that study is still in abstract form. It's not yet peer-reviewed. Yeah. It's like the fact that studies that haven't been peer-reviewed aren't even close to being peer-reviewed are being like put out there as new stories is really problematic because I can tell you as somebody who sat on the editorial boards of many journals for many years, I still sit on a few, reviewed countless papers, I've submitted and had to deal with reviews on countless papers, the fact of the matter is like until the reviews are done, the revisions are made, like that paper may never see the light of day and it may end up in a journal that you, is barely worthy of a placemat.

It might end up in a high-tier, high-quality journal, but it might not. So just because there was "a study done" means very little, but it means especially little, maybe nothing until it's peer-reviewed. Absolutely. And the methods were very poor in that study. It was a recall-based study, I think, for two days of recall of people's diets, which is notoriously very bad in terms of accuracy.

So yeah, and I think I'm not in any way suggesting that a six-hour window is the optimal window. I'm just sharing the data that suggests that compressing the window seems to have a favorable effect, and I certainly don't do six hours, but I think when you look at what the average American is doing, which is the average American has 11 eating events per day and 50% of Americans eat over a 15-hour window per day.

I can recall those because I remember when I was writing the book, I was like, "That's a long time, 15 hours and 11 events," and every time you're doing that, you're going to be stimulating this glucose rise in the bloodstream, exposing the blood vessels to that glucose. You're going to be turning on all the pathways with insulin to basically store it, and so it's strain for the body.

And so I think giving the body times intentionally to allow insulin to come down and to allow glucose to come down, what that does is it generates metabolic flexibility. It gives our body an opportunity to have space to use accessible glucose and then convert into using stored fat, and that ultimately is metabolic flexibility, the ability for the body, giving the body opportunities to use glucose but then have times when there's not high glucose and insulin around to actually get into the fat stores.

And I think one of the reasons why we have such a massive overweight and obesity rates in the country is because with the way the culture of eating right now, 11 eating events per day, eating over the course of 15 hours per day, I would imagine the average American body is rarely, if ever, tapping into their fat stores for energy in a meaningful way because we always have glucose available to the body.

If you think about, again, the stats about ultra-processed food, about 70% of the items on the shelves in the grocery store are ultra-processed food, and those ultra-processed foods are built on refined added sugars and refined added grains. So we're just – we very rarely give the body the opportunity to rest and move into fat burning.

And that's where compressing the eating window can be valuable. Obviously, people have talked about this before, but fasting can be a stressor for the body, especially if your body is not used to using fat for energy. And so it's something to ease into and go slow. But I think if you're slowing down enough to really hear what your body's signal are saying, you can kind of know whether I think your fasting is working for you or not.

I can tell. If I've got too many other things going on, I haven't slept well, a lot of stress, I can tell that fasting is kind of making me jittery and not feel good versus if I have good capacity, I can feel that it's actually making me feel really incredible.

And so tune in with your body, obviously, and you can check your biomarkers. If you have a CGM on, you can see what's happening in your glucose. If you have a ketone monitor, you can see what's happening in your ketones and really actually track, which I think makes fasting actually even more fun.

I'll mention one other piece of data that I think is actually really kind of fun as well with timing of eating. There was a study that looked at people who ate the exact same meal at 9.30 a.m. or 8.30 p.m., so basically after dark, essentially in the part of the diurnal phase when we probably shouldn't be eating versus early in the morning, 9.30.

And the glucose and insulin responses for the same meal at 8.30 p.m. were significantly higher than when eating at 9.30 a.m. And so again, bang for your buck. It appears that eating in that earlier part of the day when we're active and our chronobiology is set up for metabolism and activity, we have a lower glucose and insulin response.

There's also some evidence that melatonin, which is secreted as we get closer to sleep, has somewhat of an effect on impairing our insulin sensitivity transiently. And so we may actually just be not absorbing the glucose from those meals effectively later at night. So I tend to kind of move a little bit more low-carb, I would say, throughout the day based on that data and what I've seen on my continuous glucose monitor, basically just higher spikes for the same meal later in the day.

So why not just kind of move it up earlier?