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

Most women are told that narrower eating windows = better results, but according to Whoop’s Global Head of Performance and Science Kristen Holmes, this common advice is causing more harm than good — especially for women’s hormones. In this short episode, Kristen Holmes breaks down the science behind circadian rhythms, metabolic health, and the crucial connection between eating patterns and the menstrual cycle. What eating window works best for your body? Share your experience in the comments below, and join the conversation about women’s health and nutrition timing! Connect with Kristen Holmes: Website: https://bit.ly/4fAFT5m Instagram: https://bit.ly/41MYiIK TikTok: https://bit.ly/3Ph0qRx LinkedIn: https://bit.ly/3ByxiCl 00:00 Intro of Show 02:10 Eating Window during Menstrual Cycle 06:14 Impact of Food or Alcohol on Stress 07:57 Benefits of Circadian Alignment 10:36 An Average American is Eating in a 15-Hour Window 12:20 Mental Clarity Achieved from Fasting 13:16 Time-Restricted Eating and Hormones WHOOP - GET 1 FREE MONTH WHEN YOU JOIN!: https://bit.ly/3VQ0nzW BODY HEALTH - USE CODE “ULTIMATE20” FOR 20% OFF YOUR ORDER: http://bit.ly/4e5IjsV BAJA GOLD - 91 ESSENTIAL MINERALS PER PINCH! 10% OFF USE CODE "ULTIMATE10": https://bit.ly/3WSBqUa EIGHT SLEEP - SAVE $350 ON THE POD 4 ULTRA WITH CODE “GARY”: https://bit.ly/3WkLd6E ELEVATE YOUR WORKOUTS WITH THE ULTIMATE HUMAN STRENGTH TRAINING EQUIPMENT: https://bit.ly/3zYwtSl COLD LIFE - BOOST RECOVERY & WELL-BEING WITH THE ULTIMATE HUMAN PLUNGE: https://bit.ly/4eULUKp MASA CHIPS - GET 20% OFF YOUR FIRST $50+ ORDER: https://bit.ly/40LVY4y PARKER PASTURES - GET PREMIUM GRASS-FED MEATS TODAY: https://bit.ly/4hHcbhc HAPBEE - FEEL BETTER & PERFORM AT YOUR BEST: https://bit.ly/4a6glfo GET GARY’S WEEKLY TIPS ON HEALTH AND LIFESTYLE OPTIMIZATION: https://bit.ly/4eLDbdU SHOP GARY’S TOP-RATED PRODUCTS & EXCLUSIVE DEALS: https://theultimatehuman.com/amazon-recs Watch the “Ultimate Human Podcast” every Tuesday & Thursday at 9AM EST on YouTube: https://bit.ly/3RPQYX8 Connect with Gary Brecka: Website: https://bit.ly/4eLDbdU Instagram: https://bit.ly/3RPpnFs TikTok: https://bit.ly/4coJ8fo Facebook: https://bit.ly/464VA1H X.com: https://bit.ly/3Opc8tf LinkedIn: https://bit.ly/4hH7Ri2 SUBSCRIBE TO: https://www.youtube.com/@ultimatehumanpodcast https://www.youtube.com/@garybrecka Download the “Ultimate Human Podcast” on all your favorite podcast platforms: https://bit.ly/3RQftU0 Disclaimer: This podcast is for informational purposes only and does not provide medical advice. It is not intended for diagnosing or treating any health condition. Always consult a licensed healthcare professional before making health or wellness decisions. Gary Brecka is the owner of Ultimate Human, LLC which operates The Ultimate Human podcast and promotes certain third-party products used by Gary Brecka in his personal health and wellness protocols and daily life and for which Ultimate Human LLC and / or Gary Brecka directly or indirectly holds an economic interest or receives compensation. Accordingly, statements made by Gary Brecka and others (including on The Ultimate Human podcast) may be considered promotional in nature. Learn more about your ad choices. Visit megaphone.fm/adchoices

Speaker names marked ? are inferred from speaking time and the show’s known hosts — they are not voice-verified.

• 0:00Speaker 00

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

• 0:03Gary Brecka?

  It was astounding to me.

• 0:05Speaker 00

  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 a prioritized digestion. So all the restoration and repair that should be happening like has to basically take a backseat while we digest.

• 0:17Gary Brecka?

  Sometimes the women that have the most narrow feeding window have the highest level of hormone disruption.

• 0:24Speaker 00

  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.

• 0:42Gary Brecka?

  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 are seeing in lab values and whatnot for women.

• 0:53Speaker 00

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

• 1:08Gary Brecka?

  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. Kristin 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 Kristin Holmes.

• 1:53Gary Brecka?

  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.

• 2:09Speaker 00

  Yeah.

• 2:09Gary Brecka?

  And we started talking about time-restricted eating and we have noticed in our clinical setting that.

• 2:17Gary Brecka?

  Sometimes the women that have the most narrow feeding window have the highest level of hormone disruption.

• 2:25Speaker 00

  Yeah.

• 2:26Gary Brecka?

  So, and very likely, according to our OBGYN, has a lot to do with, you know, they can eat differently during different parts of the menstrual cycle. So, you know, 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. We've, again, it's anecdotal, but we find

• 2:55Speaker 00

  Yeah.

• 2:56Gary Brecka?

  Quite a few of these women have this issue.

• 2:58Speaker 00

  And I, and I think, I think the, there isn't a lot of research on women and 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.

• 3:21Gary Brecka?

  Mm-hmm.

• 3:22Speaker 00

  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 sonnet. When you've got all these stressors, like you are basically asking your body to do, you know, Herculean kind of level

• 3:47Gary Brecka?

  Right.

• 3:48Speaker 00

  Type of work, right?

• 3:49Gary Brecka?

  Yeah.

• 3:50Speaker 00

  It's just unnecessary, right?

• 3:51Gary Brecka?

  Agreed.

• 3:52Speaker 00

  So, 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.

• 4:00Gary Brecka?

  Right.

• 4:01Speaker 00

  And just to clarify, you know, the way I interpret the literature, there's intermittent fasting, which is, basically has a caloric restriction component.

• 4:11Gary Brecka?

  Mm-hmm.

• 4:12Speaker 00

  And then there's time restricted eating.

• 4:13Gary Brecka?

  Right.

• 4:14Speaker 00

  Which is, 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.

• 4:37Gary Brecka?

  Right.

• 4:37Speaker 00

  Regardless of what phase of the menstrual cycle they're in.

• 4:40Gary Brecka?

  Right.

• 4:40Speaker 00

  So there is, I think, a sweet spot, and it looks like it's about 10 hours.

• 4:43Gary Brecka?

  Yeah.

• 4:44Speaker 00

  Where we're eating. And then we're fasting the other 14 hours.

• 4:48Gary Brecka?

  Mm-hmm.

• 4:48Speaker 00

  And that's where, you know, people call, you know, it fasting, but it's really, it's not fasting. You're basically just giving your body a rest when it normally would be resting.

• 4:56Gary Brecka?

  Right.

• 4:57Speaker 00

  We are really, we are meant to be eating when it's light out, right? Um, or, you know, as the sun is setting, a little bit after the sun sets, you know, that is when our body is primed to metabolize food. I'm a firm believer in, you know, um, making sure you're distributing your, um, macronutrients throughout the day, um, 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 to be thinking about.

• 5:25Gary Brecka?

  So fueling in the morning, so rather than having your restricted window be, don't start eating until noon or 2, starting in the morning and stop eating earlier.

• 5:35Speaker 00

  Yeah, and it's, and I don't think when you eat necessarily is going to impact how much ga- weight you gain, like, I don't know that the evidence really, there really exists.

• 5:43Gary Brecka?

  I would agree with that.

• 5:43Speaker 00

  I, I would say that, um, that said, I think we are metabolically more primed to digest food earlier in the day.

• 5:51Gary Brecka?

  Mm-hmm.

• 5:51Speaker 00

  Right? Um, so I think, I think we know that.

• 5:54Gary Brecka?

  Certainly not late at night, right before bed.

• 5:55Speaker 00

  No, and, and, and 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.

• 6:06Gary Brecka?

  Yeah.

• 6:07Speaker 00

  You know, so when you, when you look at the, the impact on markers of sleep and recovery, um, they behave very similarly.

• 6:13Gary Brecka?

  Oh, yeah.

• 6:14Speaker 00

  Right?

• 6:14Gary Brecka?

  No, we, we, we, you know, what was interesting was, um, when we, when we did this little s- sleep challenge that, that I ran, again, super anecdotal, but, um...

• 6:26Gary Brecka?

  Feeding and alcohol, I mean alcohol almost in any amount right before bed, 100% of impact on sleep disruption, negative impact.

• 6:37Speaker 00

  And when you look at stress monitor.

• 6:38Gary Brecka?

  And the same with the food.

• 6:40Speaker 00

  Have you looked at your stress monitor? When you eat right before you go to bed, you're, you know, basically your stress monitor is like this. And then about three or four hours later, it's, you know, levels out.

• 6:51Gary Brecka?

  Right.

• 6:52Speaker 00

  But that's a great way to kind of look at the impact of your food or same with alcohol. Like you might pass out, but your stress monitor is like this until the alcohol, you know, makes its way through your system, is processed. And then you start to flatten out.

• 7:07Gary Brecka?

  Yeah.

• 7:07Speaker 00

  But it's crazy.

• 7:08Gary Brecka?

  Those were the two things that people clocked in that 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 still improved.

• 7:25Speaker 00

  Yeah.

• 7:26Gary Brecka?

  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, um, the majority of the people, you know, was below baseline. But, you know, with some people it didn't have an effect on baseline. No one that clocked in eating right before bed or having alcohol right before bed. And in our little study, which is about 8,000 or so people, um, no one, uh, did not see a detrimental effect on their sleep.

• 7:50Speaker 00

  Interesting.

• 7:51Gary Brecka?

  So those two are absolutes for me, you know, stop two hours before bed, eating and then just, you know, kind of no alcohol before bed.

• 7:57Speaker 00

  I go so far to say, I really think that like the, the benefits of just the circadian alignment piece of just literally restricting your, your eating window to 10 hours and really making sure that you're stopping your last bite a couple hours before you sleep. Viewing morning sunlight, viewing the sunset, like just those two things like can get you really far.

• 8:23Gary Brecka?

  Yeah.

• 8:23Speaker 00

  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.

• 8:27Gary Brecka?

  Yeah.

• 8:28Speaker 00

  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.

• 8:38Gary Brecka?

  Yeah.

• 8:39Speaker 00

  Like you do that, you really put yourself on a good path to improve, I think, all sorts of outcomes.

• 8:44Gary Brecka?

  I agree. And you know, I've heard you talk about this with your, you know, your previous experience with athletes and your own athletic performance that, you know, if you're ignoring the basics, sometimes we want to focus on the exotics. Everyone wants to focus on the training.

• 8:55Speaker 00

  Yeah.

• 8:56Gary Brecka?

  Everybody wants to focus on the exercise and my PR and how much I'm lifting and, um, but, and, and sleep gets tucked away. Hydration gets tucked away, nutrition gets tucked away. There's just some basic, not, you don't even have to be hyper disciplined. You know, just some basic parameters that you can shroud your day in that would dramatically, you know, improve, improve your health outcomes. But back to the time restricted eating with, with women, we, you know, we, um, we, we have tens of thousands of, of females that we actually do have blood work on. Um, and so we, you know, 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.

• 9:36Gary Brecka?

  But more than just anecdotally, in younger menstruating females that have a very tight feeding windows. And I'm going to say very tight feeding windows, less than eight hours.

• 9:48Speaker 00

  Yeah.

• 9:49Gary Brecka?

  So they report eight hours, six, some are four, and they're getting all their meals in, in four. Because either their husband or the boyfriend or something is doing it and it has

• 9:57Speaker 00

  Right.

• 9:57Gary Brecka?

  significantly less of a detrimental impact on men than it does on women. And then I, I did a podcast with Dr. Walter Longo, who's, you know, University of Southern California. He wrote The Longevity Diet.

• 10:08Speaker 00

  Yeah.

• 10:09Gary Brecka?

  I, I think he's probably the most published researcher in the world on fasting, intermittent fasting, um, um, you know, time restricted eating, fast mimicking diet. And I think he would agree with with your analysis and I know that he agrees with with mine that 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.

• 10:37Speaker 00

  The average is 15 hours.

• 10:38Gary Brecka?

  Yeah.

• 10:38Speaker 00

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

• 10:41Gary Brecka?

  Yeah.

• 10:42Speaker 00

  Like, isn't that just mind blowing?

• 10:44Gary Brecka?

  It was astounding to me.

• 10:45Speaker 00

  Now, I know, because because we're in a bubble, Gary.

• 10:47Gary Brecka?

  Yeah, no, we are in a bubble.

• 10:48Speaker 00

  We are in a bubble, okay? We did not, we're not representative of America. America is eating 15 hours a day.

• 10:54Gary Brecka?

  And and in the study that they did, people ate 17 times a day. I said, there's no freaking way people are eating 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 little mini meals.

• 11:15Speaker 00

  It just, it puts a lot of stress on our system. Like digestion is effortful, right?

• 11:19Gary Brecka?

  It's not only effortful, but evolutionarily, it's so important, right? It's it's such an important process that when the body is engaged in other activities that are necessary, like elimination of waste, repair, you know, detoxification, you know, waste elimination, by waste, I don't mean urine or stool, I mean cellular waste, right? Um, lymphatic system in the brain, the, you know, our lymphatic system, you know, eliminating waste from the body. The, when 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, it makes, or, you know, 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.

• 11:59Speaker 00

  Yeah.

• 11:59Gary Brecka?

  I'm getting nutrition.

• 12:00Speaker 00

  That's why your sleep is so messed up.

• 12:02Gary Brecka?

  Yeah.

• 12:03Speaker 00

  Because your body's having a priority digestion, divert all the resources to that. So all the restoration and repair that should be happening, like has to basically take a backseat while we digest.

• 12:13Gary Brecka?

  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 breakthroughs 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.

• 12:38Gary Brecka?

  For the first time, sometimes in their entire adult lifetime, that they actually didn't eat for a period of time. Yeah. And so. Just giving your body a break. Yeah, I'm really excited to hear, you know, what comes out of, you know, your, your research with, with whoop and what comes out of the big data at whoop, because I think what we're gonna do is, if I was to hypothesize, we're gonna see the big data at whoop support what we are seeing in, in lab values and whatnot for, 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, you know, the pituitary, which actually regulates our thyroid, our metabolism,

• 13:23Gary Brecka?

  is also regulating the menstrual cycle. Yes. Right? I mean, it's releasing luteinizing hormone, follicle stimulating hormone, and these, and men and women, by the way. So, these are regulating the production of testosterone, regulating the, 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, 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. Yep. So it drops that T4 hormone, drops a T3 hormone, and in an effort to save your life. Yes.

• 14:06Gary Brecka?

  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. Right. And although I don't personally know the direct mechanism, when, 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 dropping. Thyroid hormone levels, almost to hypothyroid levels in super narrow windows. And then the concomitant response in the menstrual cycle and they're just all over the place.

• 14:42Speaker 00

  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.

• 14:58Gary Brecka?

  So young ladies eat in a water feeding window.

• 15:01Speaker 00

  Yeah, yeah, yeah. No, let's not fast until we know more about how to do that properly.

• 15:06Gary Brecka?

  Yeah, I mean, fast once in a while, but I'm saying is the hyper restricted feeding windows.

• 15:11Speaker 00

  Like fast, you know, is plenty, you know?

• 15:15Gary Brecka?

  Awesome. Well, guys, all right. I'm sure we're gonna shut the camera off and we're gonna start it back up again. So let's just zip it. And that's just science.