Fact-Checked RFK Jr.’s Biohacking Podcast: What the Science Actually Says

When the head of U.S. health policy hosts a podcast about biohacking, peptides, stem cells, red light therapy, cold plunges, and “primal” health practices, it deserves close attention.

That is why we monitor these conversations. Not because every claim is wrong, and not because every unconventional idea should be dismissed. Some of the topics raised in this interview have real scientific evidence behind them. Heat acclimation, exercise, light-based therapies, cold exposure, and recovery practices are all legitimate areas of research.

But the problem is the way evidence gets blended with anecdote. A plausible mechanism becomes a health claim. A personal story becomes implied proof. A small or preliminary study becomes a sweeping recommendation. And when these messages come from the nation’s top health official, the distinction between curiosity, speculation, and evidence-based public health becomes especially important.

This post walks through the interview claim by claim, separating what is supported, what is overstated, and what veers into pseudoscience.

Ben Greenfield: The message that more people need to hear is the idea that a lot of these originate from natural primal practices that most people could do for free in their own backyard.

Secretary Kennedy: Hey, I’m Robert F. Kennedy Jr. Welcome to the Secretary Kennedy Podcast. My guest today is Ben Greenfield. Ben is a professional athlete, performance coach, leading voice nutrition, fitness, and preventative health. He spent years helping people improve their health through diet exercise and daily habits, focusing on practical ways to build a strength, resilience and long-term wellness. I really want you on here just to talk about biohacking, but we’ll get to that in a minute. Before we started the show, you asked me about the heat in Washington. It’s 90 degrees here today. I said that I had been to a gym this morning that didn’t have air conditioning and it was actually a good thing because it’s good to work up a sweat. You also were saying that it actually builds-

Ben Greenfield: So there is of course the increased mental demand of working out in the heat. But then if you look at what’s occurring physiologically, and this is all fresh on my mind because my 18-year-old son was complaining the other day that the AC wasn’t on our gym at home in Idaho. I told him the same thing I’ll tell you. When you look at increased heat shock protein production, which basically increases cellular resilience, when you look at increased blood volume, which is one of the direct contributors to VO2 max and probably most interestingly when you look at what Tour de France riders used to lay down in the back of buses to inject illegally EPO, erythropoietin, like a precursor to red blood cells, all of that increases when you’re working out in the heat. So if the AC’s not on at the gym, you’re basically getting a lot more out of what you’re doing at the gym, even though it sucks a lot more.

There is real evidence that heat acclimation improves thermoregulation and expands plasma volume, but the jump from “hot gym” to “basically getting more out of your workout” is too broad. Heat can increase physiological strain, and unsafe exposure to heat can increase the risk of heat illness. The better-supported claim is narrower: structured heat acclimation can improve heat tolerance and may support endurance performance in specific context

Secretary Kennedy: You’re an endurance athlete, right?

Ben Greenfield: Former, former. I’m sane. Now I’m just kettlebells

Secretary Kennedy: And walking- What is the toughest thing that you’ve

Ben Greenfield: Done? I did 13 Ironman triathlons Ironman World Championships six times. Raced professionally in obstacle course racing for Spartan for four years.

Secretary Kennedy: And what is

Ben Greenfield: That? Spartan is burpees and monkey bars and hauling sandbags up the side of mountains because they have every darn race at some kind of a ski resort at altitude. And typically running around a corner and coming face to face with whatever obstacle they’ve decided to build out in the forest or out in the middle of nowhere. And they range kind of like triathlon does from everywhere from like 30 minutes up to the death race, which was probably one of the harder events that I did, which was three days. And that was not in the heat.That was a winter death race and it was out at the Spartan CEO, Joe Desena’s farm in Vermont. And I remember my buddy dropped me off at that race and his dog wouldn’t even get out of the car because the ground was too cold. So it was 38 degrees below zero during the cold snap back east.

This would’ve been like seven years ago. And it’s just three days off. 38 below. That’s not wind chill.That’s like on the thermometer, 38 degrees below zero. And that was probably the toughest just because of the thermal management combined with going out and doing obstacles for three days in a row. So that’s up there.

Secretary Kennedy: And how many miles is that? I have no clue.

Ben Greenfield: You’re literally just doing random tasks and obstacles for three days. I mean, at one point we were in teams and dragging a canoe across a frozen lake and then wayfinding and trekking to the top of a mountain. So they just make stuff up. We probably just make stuff up. Yeah. Half of it, I think, began with someone with … Joe just wanted people to do yard chores at his farm and chop wood and haul rocks up and mountain.

Secretary Kennedy: But the Ironman is standardized.

Ben Greenfield: The Ironman is standardized. Yeah. 140.6 miles. So you swim 2.4, ride 112 and then run a marathon for dessert.

Secretary Kennedy: Yeah. My son did that in Texas last year. I went and watched him compete, which was really extraordinary.

Ben Greenfield: Yeah. I mean, they’re incredible events. I mean, what I tell people when it comes to those type of slightly masochistic events is they’re great for climbing your own personal Mount Everest and building mental resilience, but don’t fool yourself into thinking that they’re actually a healthy sport. There’s this so- called Goldilockstone of exercise where once you exceed about 75 minutes of vigorous physical intensity and most people don’t even do a minute of vigorous physical intensity per week. So most people don’t need to worry about that or 150 minutes of moderate intensity physical exercise per week. And this would be kind of like the marathon or triathlete-esque swim, bike, run protocol. You tend to see increased risk for arterial stiffness or atherosclerosis. So part of that is probably due to the inflammation, the dehydration, some of the chronic repetitive stress on the joints. Ironman it’s a great goal and a great obstacle, but probably not one of the healthiest ways to stay fit.

This is one of the more defensible claims in the interview, but it needs context. A recent systematic review found mixed evidence: some studies show higher coronary artery calcium among very high-volume endurance athletes, while others show no association or inverse associations. Importantly, exercise still strongly reduces cardiovascular and all-cause mortality overall, so this should not be read as “endurance exercise is bad,” but rather that extreme lifetime volumes may have different risk profiles than moderate activity

Secretary Kennedy: I was thinking about that because I saw there’s now a woman who’s the best long distance runner in the world for sort of ultra long distance on these 20 hour, the 30 hour race. I think some of them have 50 hour races. And it sounds like it couldn’t be good for you.

Ben Greenfield: You know this. I mean, if you like Google image search marathoner versus a sprinter, typically the sprinter has the body that looks a little bit more functional and strong and appears to be a little bit more resilient. And then if you even take me, like coming out of Ironman, when I shifted to Spartan racing, I mean, I couldn’t carry a gravel bucket up a hill. I didn’t know how to climb a rope. I could do like maybe five pull-ups. I didn’t know how to do monkey bars. You didn’t have the mobility to crawl under barbed wire. So for me, it was a wake-up call about the idea that you could look good in spandex and have a big cardiovascular engine, but that doesn’t necessarily translate to well-rounded physical health or physical fitness, I should say.

Secretary Kennedy: Let’s talk about biohacking. I spent a day with Gary Brecka in Miami at his crazy house.

Ben Greenfield: Very in the bathtub.

Secretary Kennedy: He’s got everything in that place. It’s like a hell of a spa.

Ben Greenfield: Yes.

Secretary Kennedy: But his son was there and his son had never run a marathon.

Ben Greenfield: Cole. Yeah.

Secretary Kennedy: And then I think he ran, do I remember like seven marathons in seven days?

Ben Greenfield: Seven and seven days on seven continents.

Secretary Kennedy: On seven different crimes. Which is

Ben Greenfield: The hardest part if you think about getting on an airplane after you raced a marathon.

Secretary Kennedy: Yeah. And one of them was in Antarctica, really cold and then he went right up to Egypt I think and ran it in the Sahara. But he actually- You have to

Ben Greenfield: Have a dad who’s a biohacker to pull that off. Yeah.

Secretary Kennedy: He was getting biohacked in the airplane the whole way with red lights and everything. And his father kind of did it as an experiment on him to see because he had never trained for a marathon before. I was impressed that he could pull that off.

Ben Greenfield: Yeah. If you look at biohacking, I think that a lot of the benefits of it, if we’re going to define biohacking as using science and technology and self quantification to somehow get the body to do something more quickly or more efficiently than it might be able to do in its native state, that the majority of benefits actually do come from what you were just alluding to, being able to recover faster and being able to rest more deeply. I think when you get into the exercise size of biohacking, there’s a lot of perceived shortcuts like, “Oh, I’m going to use this fancy machine and get the equivalent of a three hour run in a couple of minutes or attach electrodes to the body with electrical muscle stimulation and build muscle with just a couple 20 minute workouts a week.” And

Secretary Kennedy: Does that

Ben Greenfield: Stuff work? Well, that’s kind of what I’m getting at.You could certainly do better than if you were sedentary, but if we’re talking about functional strength and resilience, mobility and athleticism, a lot of biohacking tools could maybe be icing on the cake or something, let’s say like electrical muscle stimulation that you could do if you were injured and unable to move a joint otherwise or to retrain a muscle that would traditionally be weak, like say like the glutes or the inner quad muscle next to the knee, which is where a lot of knee pain originates in people when that’s weak. But then if you look at the recovery side, that’s where you tend to see a lot of benefit for longevity in sport and just longevity of the body in general. Everything from hyperbaric oxygen, meaning delivering oxygen into tissues so that you’ve got the ability to produce more ATP to recover more quickly or even like a non-pressurized normal barrack version of that, like exercising with oxygen therapy or alternating between hypoxia and hyperoxia using a mask.

That’s a common exercise modality that can also be used for recovery. Another example would be red light, right? That’s probably like the quintessential image that people get in their heads when they think of a biohacker, like laying in a red light bed or standing in front of a red light panel or wearing a red light hair growth helmet and there’s actually-

Secretary Kennedy: Does that work?

Ben Greenfield: Difficult to say. I use one and- You got great hair. Thanks. It’s the red light helmet. You can make a case that-

Secretary Kennedy: Are you bald when you started?

Ben Greenfield: Exactly. Photonic excitation of the follicles or the mitochondria anywhere in the body could theoretically induce some kind of regenerative or growth

Secretary Kennedy: Reduction. But is there any science?

Ben Greenfield: But one of my friends, he’s a cosmetic surgeon up in Spokane and he treats a lot of baldness and receding hairlines. And if you really truly want to grow new hair right now pretty much gold standard is you need a follicular transplant and there’s certain people that are kind of like experimenting with the idea of like a stamp or a derma roller or a microneedling pen and then smearing some peptide likes GHK copper peptide or some hair growth stimulant on there combined with red light, but it’s all pretty polyanecdotal right now when it comes to hair growth.

The hair-growth claim is more evidence-based than the interview suggests. A systematic review and meta-analysis of FDA-cleared home low-level light/laser therapy devices found randomized trial evidence of increased hair density for pattern hair loss, though the evidence base is small and device-specific. That does not mean every red-light helmet works, or that it reverses baldness broadly; it means some low-level laser devices have modest evidence for androgenetic alopecia. Yes, I was also very surprised by that

But back to the red light, that would be an example of something that does actually have evidence for collagen and elastin stimulation, for mitochondrial stimulation and for recovery. And then one other example would be something like PEMF. You ever use one of those mats, pulsed electromagnetic field therapy is what PEMF stands for and this is essentially concentrating typically like a zero to 100 hertz signal onto the body to improve electron flow, which theoretically would improve metabolic waste in and out of a cell to increase recovery or to address a muscle that’s in like a cramped or a spasm state.

PEMF has been studied for pain and soft-tissue injuries, but evidence varies by condition, device parameters, and study quality. The phrase “improve electron flow” is not a clinically established explanation for recovery benefits and should be treated as mechanistic speculation, not proven physiology

Now you look at all of those things, like those three examples I gave, which would be pretty common tools that would be called biohacking tools, oxygen, red light and PEMF. And they could accelerate recovery. They might help out with performance a little bit, but I think that the message that more people need to hear is the idea that a lot of these originate from natural primal practices that most people could do for free in their own backyard. Oxygen, just breathing hard, getting on a bike, going for a run, doing breathwork. You can actually move a lot of CO2 and oxygen just with that alone. Even just deep diaphragmatic breathing during the day, which a lot of people don’t do. With PEMF, going outside barefoot, swimming in the ocean, walking on the beach. Every time lightning strikes the surface of the planet or solar radiation bombards earth, it collects negative ions and your skin is a transdermal surface that can actually conduct electricity into the body.

So actually being outside barefoot is good for you. Swimming in the ocean, laying on your back in the backyard and stretching. You don’t have to have a fancy PEMF mat for that. Or of course the biggest, most obvious one would be red light. I mean, you get full spectrum light from the sun.

Secretary Kennedy: Including the red light.

Ben Greenfield: Including the red light. Now, of course, you have to balance that out with UVA and UVB radiation and protect your skin and not burn. But I mean, what I’m getting at is that before anybody goes out and buys like a whatever, a home soft shell hyperbaric chamber or Garybrech is super cool, hard shell one that you can work out in or uses a PEMF mat or a PMF tool or buys a fancy red light bed or red light panel. I mean, go outside, get sunlight, do some breath work or difficult cardiovascular stimulus for the lungs so that there’s a lot of low hanging fruit is what I’m saying before you get to biohacking. And I think the message more people need to hear is just like, move your body and go outside.

Secretary Kennedy: What about peptides?

Ben Greenfield: That would certainly fit into the category of biohacking. So as you know, peptides are super popular right now. I think they’re one of the most Google search terms recently surpassing pickleball. I use peptides. I’ve messed around with peptides since 2016, everything from BPC-157 and TB500 for injuries or thymus and alpha-1 for the immune system or things like SS31 or MOTC. They all have Star Wars R2D2C3PO names that are difficult to remember. But the idea with peptides is that they’re very small chains of amino acids that can act with pretty good precision on specific cellular targets, specific cellular receptors and they seem to work for a lot of people. I think they also need more research. I think that they’re a very promising tool. I’ve used them successfully for a really long time, but I think-

This section needs strong caution. Some peptides are real, evidence-based medicines, but many popular “biohacking” peptides are not FDA-approved for the uses being discussed and lack robust human clinical trials. FDA has specifically flagged BPC-157 as a substance with potential safety risks in compounding, including immunogenicity concerns, peptide-related impurities, and limited safety information for proposed routes of administration.

Secretary Kennedy: What do you mean successfully?

Ben Greenfield: Injecting a joint that I know would have taken a much longer time to

Secretary Kennedy: Repair if I

Ben Greenfield: Hadn’t used something like BPC157 or TB500 or being anxious just due to a high stress workday and using something like intranasal C link or injecting C length as an anxiolytic or even using something like CMax for improving cognition or verbal fluency, but a lot of this is anecdotal. I think it would be nice-

Secretary Kennedy: But you think you can see a result. I

Ben Greenfield: Know I can see a result with peptides. Absolutely. Yeah. And of course I’m not the only one talking about the success that they’ve had with peptides. I think there just needs to be more research and more structured research done on the safety and efficacy and protocols around peptides, whether that’s like probably be the root of something like IRBs or some type of scenario where a physician, a prescribing physician in a clinic would be able to actually use peptides as something like a research study in a safe environment. I think that’s a much better route than what’s going on to a great extent right now, which is people hear about peptides and then they go and Google peptides and they find them on the gray market sold for human research. And when you sell something for human research, you’re not even allowed to give out prescribing information about it.

So people are at home just like trying to figure out how to inject themselves with something safely because there’s very little oversight from a doctor about how to do it. And that’s where you hear the horror stories of somebody just getting some sepsis-like condition because they didn’t even know they were supposed to use an alcohol swab on the rubber stopper or on their skin before they pulled something up into a syringe or worse yet getting something that has no certificate of analysis and you don’t know where it came from and you don’t know the sterility procedure used to produce that peptide. So I think production of peptides and oversight, especially from some kind of a research avenue to figure out what’s working and what isn’t and what physician protocols would actually be good to use is necessary in the peptide world because it’s a little bit of the wild, wild west right now, but I don’t think they’re bad just having subjectively used them for a long time.

Secretary Kennedy: I mean, you could make the same argument on the supplements. None of those are tested in clinical trials.

Ben Greenfield: Right, exactly.

Secretary Kennedy: The FDA only has the authority to regulate drugs that claim a particular indication. And so as long as they don’t claim an indication, they’re supposed to be, if a doctor prescribes them there, he’s supposed to be able to do that without any clinical trials.

Ben Greenfield: Yeah. I think a lot of doctors still need more education around peptides though. I mean, a lot of doctors just aren’t even familiar with the protocols or what they do. And so yeah, they’re considered to be just kind of like dark and scary and unknown for a lot of doctors. So I think-

Secretary Kennedy: And stem cells.

Ben Greenfield: I’ve done stem cells kind of very similarly similar to like the biohacking idea from a regenerative standpoint, I’ve had a lot of good results. For example, from all the crazy masochistic Ironman stuff, I had full-on arthritis in my left knee and rather than opting for a knee replacement, this was like seven years ago, super swollen left knee. I couldn’t squat, couldn’t play tennis, couldn’t play pickleball. I wound up getting what’s called an intraosseous needling procedure where a doctor essentially drilled holes, almost like aerating a lawn on the two articulating surfaces in the knee joint and then filled that with stem cells as like a cartilage regeneration protocol and my knees are great now and that’s what turned the corner for me. I’ve also done stem cell infusions and stem cell injections in other joints. And again, I think that it’s a pretty nuanced discussion because there’s a lot of different forms of stem cells.

There are many international clinics where I know people have gotten hurt from a procedure or been infected from a procedure and they’re still like growing multiple generations of stem cell lines at many of those clinics, which increases the carcinogenicity of a stem cell population every time that you regrow or reexpand a stem cell line. So I think you need to know where you’re getting your stem cells and who’s administering them, but I think they hold a lot of promise, particularly for joint regeneration and potentially for organ regeneration.

Come on. A personal recovery story is not the same as evidence of cartilage regeneration. The FDA states that regenerative medicine products have not been approved for orthopedic conditions such as osteoarthritis, tendonitis, disc disease, knee pain, or shoulder pain, and warns of risks including infection, tumor formation, neurological events, and blindness when products are illegally marketed.

Secretary Kennedy: Anything outside of those categories?

Ben Greenfield: Outside of stem cells, peptides, and supplements from a biohacking standpoint? I think the idea, if we want to look at it from maybe like a central nervous system, vagus nerve anxiolytic standpoint, there’s a lot in the category of brainwave entrainment or relaxation or even

Downregulation of the default mode network, the type of things that people would often look for or look to opioids, muscle relaxants, diazepams, or even from a default mode network, plant medicines to achieve from a mental standpoint that you can stimulate with technology. If you look at the vagus nerve, for example, I don’t know if you wear a device or measure your heart rate variability or recovery or anything like that, but HRV is a commonly measured metric for recovery. It’s the delta between each heartbeat. So the idea is that if you have a lot of variation in between each beat of your heart, you have high heart rate variability and if it’s very, very mild or low beat to beat variation, you have low heart rate variability and high HRV is an indicator that the sympathetic and parasympathetic branches of your nervous system are communicating well with the cytoatrial nodes of your heart, basically with your cardiac pacemaker cells.

And if that occurs, that’s a good sign that you’re recovered. And if you’re very stressed and you’re engaging in shallow breathing throughout the day and you’re just basically living in the anxious state that a lot of Americans live in every day, you would tend to see low heart rate variability. And the general recommendation from a non-biohacking standpoint would be breathwork, yoga, working on your relationships, getting a good night of sleep, de- stressing, not working too hard, and those are all great. And then if you delve into the world of something like biohacking, you have, for example, the ability to use electronic vagal nerve stimulation, meaning like electrodes directly over the uricular branch of the vagus nerve slightly behind the ear to be able to induce relaxation or high HRV by directly stimulating that. Cold water face dunks or cold baths or cold soaks, which kind of fit into the biohacking category, those would also be something that would stimulate the vagus nerve.

You can even use light. There are machines that will use a light spectrum very similar to what you’d get from a red light bed or red light panel, but they’re directly over either side of the neck. That’s one example. Another example would be light sound stimulation and also haptic stimulation. There is a chair that’s very common for someone with PTSD, someone with low HRV or someone who just basically has difficulty turning their brain off. It’s basically like a gravity chair that’s lined with

Secretary Kennedy: Vibration. I’ve seen those.

Ben Greenfield: Yeah. And you wear earphones.

Secretary Kennedy: You wear eye mask,

Ben Greenfield: You wear earphones. I have one next to my office in the room next to my office and you sit in that thing and it just, even in a racing brain or somebody who’s just like hard charging, high achieving, can’t turn things off, you sit in that thing and you just relax. There’s a little ankle band that I travel with that does something very similar. You lay in bed and it kind of vibrates the body into this relaxed state that a lot of people would normally rely on like a glass of wine or a Valium to achieve and this is just using technology without any biochemical payback. Final example would be using light and sound. So this is down to like the default mode network piece. A lot of people will shift the brain into a more malleable state or increase neuroplasticity or decrease beta brainwaves and increase something like focused alpha brainwaves or creative theta brainwaves using in many cases it’ll be like psilocybin, LSD, plant medicines, a lot of these things that might work for those conditions, but that also require hefty amount of time off work or you’re not going to do that at noon and be back at work at 1: 00 PM after lunch break.

You can use light and sound to shift the body into a very similar state. It’s a lamp that you lay underneath that flashes light, almost like a strobe light, and you’ve got your eyes closed, but it’s shifting your body into that same state. There are headworn devices like the brain tap or the visor and these would be more like travel friendly versions of almost like these goggles that you wear that people will sit up from and say they feel like they’ve done something like a psilocybin journey without actually doing that, but more important than anything psychedelic or entheogenic is the idea that it shifts the brain. Yo feel more relaxed, you feel more creative, you feel more neuroplastic depending on the reason that you’ve actually done a session like that. Long answer to your question, but I would say another category would be just the use of technology instead of drugs to induce a certain mental state.

Secretary Kennedy: And have you used that stuff successfully?

Ben Greenfield: Yeah. And they don’t work better if you combine them with drugs. I know people who have tried.

Secretary Kennedy: How about the cold plunges?

Ben Greenfield: Cold plunges? Well- They build character. Yeah, they build character. So cold plunges get a bad rap I think mostly by people who don’t like to be cold. And very similar to what we were talking about with heat, heat shock protein and erythropoietin and cardiovascular blood flow, you see a multitude of benefits that occur from thermal stress in general. And there’s obviously two sides of the coin when it comes to thermal stress, heat and cold. And with cold, you see some different mechanisms. You see an acute, an immediate vasoconstrictive response as the body goes into like this sympathetic stressed out mode followed by this vasodilatory rush. Anybody who’s gotten out of like a cold plunge or a cold shower, your skin kind of looks a little lobster red afterwards. And the reason is that rebound vasodilatory blood flow that occurs that’s actually good for cardiovascular health.

I wear a continuous blood glucose monitor and a lot of people are familiar with the type of things that would keep blood glucose stabilized. Going for a walk before and after a meal, lifting weights or maintaining muscle, which acts as kind of like a sink for extra glucose.

Even certain herbs or drugs like Barbarine as an herb or metformin as a drug, all of these can impact your blood glucose variability. But one thing that surprised me when I started wearing a CGM, a continuous glucose monitor, is how effective cold is at stabilizing blood glucose. It seems to have a pretty profound insulin sensitizing effect and that could be like a cold shower before you’re going to go out to a steakhouse at night and punish some of the bread bowl. It could be a morning cold plunge after a sauna session, but the glucose stabilizing effect of cold is one interesting factor that a lot of people don’t think about.

Cold exposure can activate brown adipose tissue and may affect glucose and lipid metabolism, but the human evidence is still limited. A 2024 systematic review and meta-analysis found only seven eligible studies with 85 total participants and did not find significant fasting changes in glucose, insulin, or triglycerides under cold exposure compared with thermoneutral conditions. So “profound insulin sensitizing effect” is stronger than the current evidence supports.

Another one, and this is especially interesting when you look at the fact that now we’re blessed to live in this post-industrial modern era where we live and drive and sleep and work in temperature controlled boxes, right?

It’s 90 some degrees in DC right now and we’re at a comfortable 68 or whatever in here. But from a resilience standpoint, the idea of being constantly comfortable, that doesn’t necessarily do the body any metabolic favors. So when you are in the cold, you see a shift of metabolically inactive white adipose tissue to metabolically active brown fat. Some influencers will blow its way out of proportion and say, “Well, you’re going to burn an entire cheesecake in the cold plunge,” and that’s not true. You do see a slight increase in metabolic rate and a slight improvement in blood glucose stability that lends itself to better metabolic health, pushback by a lot of people as well as stressful. It’s like sending your body in a battle every morning, if you’re going to go jump in a cold plunge and furthermore, the second thing people say is, well, it blunts the body’s response to your workout.

If you get in a cold plunge or you get cold after a workout, you will see less mitochondrial proliferation and you’ll see less building of satellite cells which help to grow new muscle. That claim is true and so is the claim about it being excessively stressful, but for the claim about cold being excessively stressful, what you actually see in long-term studies on cold is for about the first four weeks you get a cortisol response and your body gets very sympathetic and then over time you develop the ability to have lower cortisol throughout the day and better nervous system resilience, meaning back to that HRV thing that I mentioned if you have a regular cold practice and then with the don’t get cold after workout bro thing that people say, yes, that’s true. And if you look at the actual studies that put people in cold water or in a cold room after a workout, they’re leaving them in there for like 10 to 20 minutes and you’re seeing like a muscle temperature drop of one degree or more Celsius that’s inducing that blunting of the natural stress response that you’d normally want the body to have after workout.

This claim has some support: cold-water immersion after resistance training may reduce some hypertrophy-related adaptations, especially when used repeatedly and close to training. But the practical relevance depends on timing, duration, temperature, and whether the goal is muscle growth, soreness reduction, or recovery between competitions.

I don’t know a lot of people who are going into a cold plunge for like 10 to 20 minutes after a workout. So the idea of just like cooling off the body for two or three minutes by taking a quick cold shower or even just like waiting until later in the day after your workout and doing a cold plunge after an afternoon sauna or something like that is fine. I’m a huge fan of cold plunging and I live in Idaho, so I have to be a fan of the cold anyway.

Secretary Kennedy: And what do you think about all the fascination that we’re seeing now with longevity?

Ben Greenfield: It’s interesting. There’s almost like this near transhumanistic obsession with grasping at immortality, right? So how much more can you do in your elaborate five hour morning routine to get just a few extra weeks or months or years of life? And some of it’s a little bit ironic because, and I’m sure you know people like this, it seems like all those extra years that people are trying to get are spent in a hyperbaric chamber, huddled up cold and hungry and libidalists inside some kind of a HVAC pod. And it’s kind of ridiculous if you step back and look at it that way because I mean Lord of the Rings, right? Golum lived a long time, lived a really long time, wasn’t necessarily the happiest, most fulfilled character in that book, but he had the longevity game nailed down pretty good. I think that rather than myopically focusing on living as long as possible, which can be a relatively unfulfilling pursuit at the end of the day, we should be focusing at putting more health into the years that we do have.

I don’t know how long I’m programmed to live if we want to look at things from a genetic standpoint. I think I could certainly live a little bit longer using some of the natural and the scientific protocols that we’ve been talking about, but more importantly, I want to be able to throw a football around the backyard with my grandkids and climb a mountain and hang out and go on vacations with my wife and just be robust and vital and fit for as long as possible, as close as possible to the day that I die. And considering that the longest livid human being on record I think is like 117 years old to claim that somehow in like the next decade we’re going to get that to like 130 or 140 or 150 or 180 is I think a little bit ridiculous and we should be focusing more on A, just remaining reasonably vital without it becoming a selfish pursuit and B, filling our lives with those things that are also just as much if not more fulfilling than the pursuit of longevity, staying out past your bedtime with the family and spending more time with loved ones and building relationships and throwing family dinners and doing all the things that we know, I mean, even based on like Harvard’s longest running study on longevity trump all of the PMF and the oxygen and peptides and the stem cells and the red light and that’s the amount of and the quality of love and relationships in your life.

So I’m not opposed to living healthy, but I do think that some people kind of like take it too far.

This is the most grounded public-health point in the episode. The Harvard Study of Adult Development has long emphasized that strong relationships are associated with health and well-being across the life course. Unlike many biohacking interventions discussed here, social connection is low-cost, broadly relevant, and supported by decades of longitudinal research.

Secretary Kennedy: So you’re not going to move in with Brian Johnson?

Ben Greenfield: I mean, if he invited me, I’d probably go for a few days just to see what it was like. Yeah. Yeah. I’d probably head home to Idaho pretty quick.

Secretary Kennedy: Ben, thank you very, very much.

Ben Greenfield: Thanks for having me on.

Secretary Kennedy: It’s a

Ben Greenfield: Pleasure.

Secretary Kennedy: Really, really good fun. Thank you.

Ben Greenfield: Thanks.