128. Kristen Holmes: The TRUTH About Women's Fasting Windows (Science Says You're Doing It Wrong)

The average American is eating over the course of 15 hours. It was astounding to me.
It puts a lot of stress on our system. Like digestion is effortful.
That's why your sleep is so messed up because your body's having to prioritize digestion. So all the restoration and repair that should be happening like has to basically take a backseat while we digest.
Sometimes the women that have the most narrow feeding window have the highest level of hormone disruption. These really narrow eating windows put a lot of stress on the body.
When people restrict their feeding window to 10 hours, they have better markers of sleep and better markers of recovery, regardless of what phase of the menstrual cycle they're in. Fueling for your activities, to me, is the principle that all women need to be thinking about.
I'm really excited to hear what comes out of your research with Whoop.

If I was to hypothesize, we're going to see the big data at Whoop

support what we're seeing in lab values and whatnot for women.

I think there isn't a lot of research on...

Hey guys, welcome back to the ultimate human podcast where we go down the road of everything anti-aging biohacking longevity and everything in between um kristen holmes who's been on the podcast before came back for a short because we just thought it was so important to do a short anecdotal review of our discussion on time-restricted eating and the female menstrual cycle. She's working on some really interesting things at WHOOP, which aren't ready for public dissemination yet, but using big data to look at how wearables can actually track the menstrual cycle in women and may be a potential alternative to birth control.
And then we started to go down the road of time-restricted eating. So I hope you enjoy this short podcast with Kristen Holmes.
You know, one of the things I have been trying to do is increase the appeal to my female audience and not just get more women onto the podcast, but talk more about women's issues, things that are important to women that the biohacking space is sort of negating. And we started talking about time-restricted eating, and we have noticed in our clinical setting that sometimes the women that have the most narrow feeding window have the highest level of hormone disruption.
And very likely, according to our OBGYN, has a lot to do with they can eat differently during different parts of the menstrual cycle. So if they wanted to sort of like accordion expand and contract their feeding window, which is a little difficult to do.
But a lot of these young women that just adopt strict intermittent fasting

and they're very militant about it, their hormones go into a tailspin.

Again, it's anecdotal, but we find quite a few of these women have this issue.

And I think there isn't a lot of research on women in intermittent fasting. A lot of the research is in men.
So there's still so much more that I think we have to do. But I do think a lot of the women, a lot of the researchers in this space would say that these really narrow eating windows put a lot of stress on the body.
And especially during the luteal phase, for example, the couple of weeks leading into menses, your body is already working really, really hard. It's a metabolically super expensive time.
So when we're layering on other stress, we're intermittent fasting, we're exercising, we're doing cold plunge, we're doing sauna. When you've got all these stressors, you are basically asking your body to do Herculean kind of level type of work.

It's just unnecessary. Agreed.
So I think, again, given that the research isn't quite there yet, I think there is a case to be made that during the luteal phase, not a time to have a really narrow eating window. Right.
And just to clarify, you know, the way I interpret the literature, there's intermittent fasting, which basically has a caloric restriction component. And then there's time-restricted eating, which has a circadian component.
And I'm not a nutritionist and I'm not an expert in fasting, but my PhD was in circadian alignment, predicts psychological and physiological resilience. So I spent a lot of time on circadian things.
And I have seen in the data, when people restrict their feeding window to 10 hours, they have better markers of sleep and better markers of recovery, regardless of what phase of the menstrual cycle they're in. So there is, I think, a sweet spot, and it looks like it's about 10 hours where we're eating.
And then we're fasting the other 14 hours, and that's where people call it fasting. But it's really not fasting.
You're basically just giving your body a rest when it normally would be resting. We are meant to be eating when it's light out, or as the sun is setting a little bit after the sun sets.
that is when our body is primed to metabolize food. I'm a firm believer in making sure you're distributing your macronutrients throughout the day, biasing toward a little bit earlier in the day when you're going to be most active, fueling for requirements, like for your activities, to me is the principle that all women need me think about.
In the morning. So rather than having your restricted window be, don't start eating until noon or two, starting in the morning and stop eating earlier.
Yeah. And I don't think when you eat necessarily is going to impact how much weight you gain.
Like, I don't know that the evidence really, there really exists. I would agree with that.
I would say that, um, that said, I think we are metabolically more primed to digest food earlier in the day. Right.
Um, so I think, I think we know that late at night, right before when I look at the data, I, you know, it is just, it literally eating a meal two hours before bedtime is the same pretty much as drinking alcohol two hours before bedtime. So when you look at the impact on markers of sleep and recovery, they behave very similarly.
Oh, yeah. No, what was interesting was when we did this little sleep challenge that I ran, again, super anecdotal, but feeding and alcohol, I mean, alcohol almost in any amount right before bed, 100% impact on sleep disruption, negative impact.
And when you look at stress monitor, it's insane. Same with the food.
Have you looked at your stress monitor? Yeah. When you eat right before you go to bed Basically, your stress monitor is like this.
And then about three or four hours later, it levels out. But that's a great way to kind of look at the impact of your food or same with alcohol.
You might pass out, but your stress monitor is like this until the alcohol makes its way through your system, is And then you start to flatten out. Yeah.
But it's crazy. Those were the two things that people clocked in that, um, not only had no effect on baseline had negative effect on baseline.
And there was a two that were consistent. Like they didn't change the temperature of the room.
Sometimes the sleep score actually still improved. They didn't darken the room so much.
Sometimes sleep score score still improved. They didn't do like the breath work or the contrast shower.
Some people even reported using screen time in bed and it didn't. The majority of the people, you know, it was below baseline, but you know, some people didn't have an effect on baseline.
No one that clocked in eating right before bed or having alcohol right before bed. In our little study, which is about 8,000 or so people, no one did not see a detrimental effect on their sleep.
So those two are absolutes for me. Stop two hours before bed eating and then just kind of no alcohol before bed.
I go so far to say I really think that the benefits of just the circadian alignment piece of just literally restricting your eating window to 10 hours and really making sure that you're stopping your last bite a couple hours before you sleep. Yeah.
Viewing morning sunlight, viewing the sunset, like just those two things like can get you really far. Yeah.
And they're both free, right? Like it's not, you're not changing the quality and content of your food. Obviously that really matters.
But for people who don't, who can't afford it, everyone can pretty much get outside within 20 minutes of waking up. Pretty much everyone can watch the sunset for the most part.
And people can narrow their feeding window to 10 hours for the most part. Yeah.
Like you do that. You really put yourself on a good path to improve, I think, all sorts of outcomes.
I agree. And, you heard you talk about this with your previous experience with athletes and your own athletic performance that if you're ignoring the basics, sometimes we want to focus on the exotics.
Everyone wants to focus on the training. Everybody wants to focus on the exercise and my PR and how much I'm lifting.
And sleep gets tucked away. Hydration gets tucked away.
Nutrition gets tucked away. There's just some basic...
You don't even have to be hyper-disciplined, just some basic parameters that you can shroud your day in that would dramatically improve your health outcomes. But back to the time-restricted eating with women, we have tens of thousands of females that we actually do have blood work on.
And so we pull 74 biomarkers, then we pull 10 to 12 weeks later, we pull the same 74 biomarkers and we'll look at changes in those biomarkers. But more than just anecdotally, in younger menstruating females that have very tight feeding windows, and I'm going to say very tight feeding windows, less than eight hours.
Yeah. Like four or six.
Eight hours, six, somewhere at four, and they're getting all their meals in four because either their husband or the boyfriend or something is doing it. And it has significantly less of a detrimental impact on men than it does on women.
And then I did a podcast with Dr. Walter Longo, who's at the University of Southern California.
He wrote The Longevity Diet. I think he's probably the most published researcher in the world on fasting, intermittent fasting, time-restricted eating, fast-mimicking diets.
And I think he would agree with your analysis. And I know that he agrees with mine that even 10 to 12 hours.

But when he said as wide as 12 hours, I was like, isn't everybody eating in 12 hours?

He said, actually, no, most people start eating right when they get up in the morning and they do not stop eating until 11 o'clock at night. The average is 15 hours.

Yeah.

The average American is eating over the course of 15 hours.

Yeah.

Like, isn't that just mind-blowing?

It was astounding to me.

No, I know, because we're in a bubble, Gary.

Yeah, we are in a bubble.

We are in a bubble, okay?

We don I know.

Because we're in a bubble, Gary.

No, we are in a bubble.

We are in a bubble, okay?

We're not representative of America.

America is eating 15 hours a day.

And in the study that they did, people ate 17 times a day.

I said, there's no freaking way people eat 17 times a day.

He said, yeah, 17 times a day.

They might have three big meals, but there are 17 times that they are consciously ingesting food i don't mean just throwing a you know starburst in their mouth i mean actually eating it just puts a lot of stress on our system like digestion is effortful right it's not only effortful but evolutionarily it's so important right it's yeah it's such an important process that when the body is engaged in other activities that are necessary like elimination of waste, repair, detoxification, waste elimination. By waste I don't mean urine or stool, I mean cellular waste, right? The lymphatic system in the brain, our lymphatic system eliminating waste from the body.
When we ingest food, those processes come to a grinding halt because the shift becomes the priority of digestion. And if you think about it evolutionarily, ancestrally, it makes a lot of sense.
We didn't know when we were going to get our next meal. So when you ate, the body was like, this is a priority.
Yeah, and that's what's happening to sleep. That's why your sleep is so messed up because your body's having to prioritize digestion yeah divert all the resources to that so all the restore restoration and repair that should be happening like has to basically take a backseat while we digest yeah so your body's on on its way to doing something else and you shift it back to digestion it's on its way to doing something else you shift it back to digestion you know even even when we did these short-term fasting challenges most of the breakthroughss happened on days two and three, and people were like, whoa, like the level of mental clarity, like a light bulb just went on.
And I felt cognizant, clear, clean, awake. It was for the first time sometimes in their entire adult lifetime that they actually didn't eat for a period of time.
Yeah. Just giving your body a break.
Yeah. I'm really excited to hear what comes out of your research with WHOOP and what comes out of the big data at WHOOP because I think what we're going to do is, if I was to hypothesize, we're going to see the big data at WHOOP support what we're seeing in lab values and whatnot for women.
So better for them to just restrict their calories over a longer period of time than to pile them in into a very shortened window. And what we also see on the labs is the pituitary, which actually regulates our thyroid, our metabolism, is also regulating in the menstrual cycle.
Yes. I mean, it's releasing luteinizing hormone, follicle-stimulating hormone.
And men and women, by the way, so these are regulating the production of testosterone, they're regulating the cycle, how they go from ovulation to follicular to luteal phase. And so one of the interesting things about time-restricted eating and the pituitary is if you don't eat very often or you don't eat in a wide enough window, the pituitary begins to slow down the thyroid.
It starts to throttle back the metabolism. So it drops that T4 hormone, drops the T3 hormone, and in an effort to save your life because it perceives low blood sugar over a prolonged period of time as starvation.
Yeah. And it's like, well, we better save this person.
So, and although I don't personally know the direct mechanism, when it's restricting the function of the thyroid, it can also restrict through luteinizing hormone and follicle stimulating hormone it can also throw the menstrual cycle off right because we see the drop in thyroid hormone levels um almost to hypothyroid levels um in super narrow windows and then the concomitant response in the menstrual cycle and they're just all over the place and that's why i see you know when we're restricting calories like you don't it's not safe for you to have a baby so you don't get your menstrual you don't get your period you're not gonna ovulate right like so all these things like start to shut down because you know it's not a safe environment to have a baby so your body's really smart in that way young ladies eat in a water feeding window yeah yeah no let's not fast until we know more about how to do that properly.

Yeah, I mean, you fast once in a while.

But I'm saying is the hyper-restricted feeding windows.

But usually a 14-hour fast is plenty.

Beautiful.

Awesome.

Yeah.

Well, guys, all right.

I'm sure we're going to shut the camera off.

I know, I know.

And we're going to start it back up again.

So let's just do it.

Yep.

And that's just science.