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Greetings!
Welcome to the Physiology Friday newsletter.
ICYMI
Check out my guest appearance on The Neuro Experience podcast with Louisa Nicola, where we talk about the science of VÌO2 max.
On Wednesday, I published a post about some of the most common myths about coffee and caffeine.
Details about the sponsors of this newsletter including Examine.com and my book âVO2 Max Essentialsâ can be found at the end of the post!
Physiologically Speaking is a reader-supported publication. To receive new posts and support my work, consider becoming a free or paid subscriber.
If you can fill the unforgiving minute
With sixty secondsâ worth of distance run,
Yours is the Earth and everything thatâs in it,
Andâwhich is moreâyouâll be a Man, my son!
â Rudyard Kipling, Ifâ
In my book âVO2 Max Essentialsâ, I make the case for why cardiorespiratory fitness should be considered the most important vital sign. Among all risk factors, VÌO2 max is the only one thatâs a composite of multiple physiological systems, rather than a snapshot of health at one point in time or a single biomarker measured via a blood test.
Your maximal oxygen utilization capacity (VÌO2 max) represents the maximum integrated capacity of the pulmonary, cardiovascular, and muscular systems to uptake, transport, and utilize oxygen during whole-body, dynamic exercise. The function of your autonomic nervous system, your heart and blood vessels, your lungs, your muscles, and your mitochondria all influence your maximal aerobic capacity. Itâs not just a strong heart that gives someone a high VÌO2 max. A strong body is a prerequisite.
This is, in my opinion, why a high VÌO2 max is so often associated with beneficial health outcomes. You wonât find someone with a high VÌO2 max who is in poor health, and often people with an extremely low VÌO2 max are in poor health.
Though itâs not routinely measured in clinical practice (yet), VÌO2 max has recently appeared on the radar of many healthcare professionals. People are becoming aware of the predictive power of cardiorespiratory fitness and are increasingly interested in how (and why) to improve it.
Over the last 20 years, evidence has emerged linking higher cardiorespiratory fitness to lower risks of all-cause mortality and other diseases. Thus, itâs about time we had a scoping review of the evidence, which brings us to todayâs study.
The study, published in the British Journal of Sports Medicine was an overview of all previously published systematic reviews and meta-analyses on the relationship between VÌO2 max and an array of health outcomes.
The studies were eligible if they included adults with or without health conditions and measured cardiorespiratory fitness using a maximal graded exercise test, a maximal or submaximal exercise test with a prediction equation (i.e., without direct measures of gas exchange), or a non-exercise prediction equation. When pooling the data and examining the outcomes, the authors compared the groups with the highest cardiorespiratory fitness to those with the lowest cardiorespiratory fitness.
Overall, a total of 26 studies with over 20.9 million participants from 199 different cohorts were included in the review.
Eight of the included studies examined the association between VÌO2 max and death (mortality) from all causes, cardiovascular disease, sudden cardiac events, all cancers, and lung cancer.
Compared to low cardiorespiratory fitness, having high cardiorespiratory fitness was associated with a 41% to 53% lower risk for premature mortality. Furthermore, each 1 metabolic equivalent (MET) increase in cardiorespiratory fitness (1 MET is equal to an increase in VÌO2 max of 3.5 mL/kg/min) reduced the risk of premature mortality by 7% (all cancers) to 51% (sudden cardiac mortality).
A notable limitation for mortality outcomes was the large disparity in male vs. female participants â more than 1.8 million male participants were included in the studies while only 180,000 females were included.
Having a higher cardiorespiratory fitness was also associated with a lower risk of developing hypertension, heart failure, stroke, atrial fibrillation dementia, kidney disease, depression, and type 2 diabetes. Specifically, the risk of a new onset condition was 37% (hypertension) to 69% (heart failure) lower when comparing high vs. low cardiorespiratory fitness.
For every 1 MET increase in fitness, the risk of developing a new chronic health condition was reduced by 3% (stroke) to 18% (heart failure).
Similar to mortality outcomes, a majority of the evidence was from male populations, although two studies investigated the effects in female-only cohorts. In these groups, high cardiorespiratory fitness was found to be more protective against stroke and type 2 diabetes among females compared to males. Among men, a higher cardiorespiratory fitness was not associated with prostate cancer risk.
What about individuals who already have a chronic health condition? Does having a high cardiorespiratory fitness protect them from early death or adverse events?
This seems to be the case. A lower risk of premature death or adverse events was observed for people with a higher vs. a lower cardiorespiratory fitness and ranged from 19% (for an adverse event among adults with pulmonary hypertension) to 73% (for cardiovascular mortality among people living with cardiovascular disease).
Based on this comprehensive review, not only does having a higher cardiorespiratory fitness reduce the risk of premature death from all causes, but it also reduces the risk of developing a new condition or dying from a condition you already have.
Put another way, low fitness is a consistent and important risk factor for early death and chronic disease.
If this isnât enough evidence that cardiorespiratory fitness should be considered a vital sign, I donât know what is. The authors even suggest that a minimum clinically important difference or MCID for VÌO2 max be established as 1 MET (3.5 mL/kg/min). Exercise trials and other interventions can be deemed âeffectiveâ if the participants achieve this degree of fitness improvement. Itâs a goal you should strive for in your own exercise regimen.
Because this was merely an overview of published literature, we unfortunately donât have specific numbers for the âhighâ and âlowâ VÌO2 max groups. But I did a quick scan of the included studies on mortality risk to find a quick estimate.
Low cardiorespiratory fitness is somewhere in the range of less than 8â9.5 METs or a VÌO2 max of less than 28â33 mL/kg/min. High cardiorespiratory fitness is about 11â13.7 METs or more, or a VÌO2 max of 38.5â48. If youâre below or near one of these categories, act accordingly.
The certainty (quality) of the evidence was also downgraded mostly due to a large variation in how the studies measured VÌO2 max and the large proportion of male participants. And, of course, the main limitation is that these associations (correlations) may not imply causation.
One of the main criticisms of this literature is that, because nearly 50% of oneâs VÌO2 max can be explained by genetics and is therefore unmodifiable, the association between cardiorespiratory fitness and healthspan/longevity may not represent an effect of a high fitness level per se, but rather, an underlying predisposition to health. Healthy people have a higher VÌO2 max, but theyâre not healthy because of it.
I donât buy this. To explain why, Iâll use the Bradford Hill criteria.
The Bradford Hill criteria, also known as Hillâs criteria for causation, are a set of nine principles used to establish epidemiologic evidence of a causal relationship between a presumed cause and an observed effect. These criteria have been widely used in public health research and were proposed by the English epidemiologist Sir Austin Bradford Hill in 1965.
The nine criteria are:
* Strength (Effect Size)
A small association does not rule out causality, but a stronger association increases the likelihood of a causal effect.
* Consistency (Reproducibility)
Consistent findings across different studies, populations, and settings strengthen the evidence for causality.
* Specificity
A specific association between a factor and an effect suggests a higher probability of a causal relationship.
* Temporality
The cause must precede the effect in time
* Biological Gradient (Dose-Response Relationship)
Generally, greater exposure leads to a higher incidence of the effect.
* Plausibility
A plausible mechanism linking cause and effect enhances the evidence.
* Coherence
Consistency between epidemiological findings and laboratory evidence strengthens the likelihood of causality.
* Experiment
Experimental evidence can support causality.
* Analogy
Similarities between the observed association and other known causal relationships can provide additional support.
Now, letâs apply the Bradford Hill criteria to VÌO2 max.
* Strength of Association
Numerous studies consistently demonstrate a strong inverse relationship between cardiorespiratory fitness and mortality risk. Case in point: this review.
* Consistency of Effect
Research findings consistently support the link between fitness and health outcomes. Multiple studies across diverse populations consistently show that better fitness is associated with improved health and longevity. Again: see this review.
* Specificity
While cardiorespiratory fitness impacts overall health, it specifically reduces the risk of cardiovascular diseases, diabetes, and certain cancers.
* Temporality
The temporal relationship is well-established: higher fitness precedes better health outcomes. Individuals who maintain or improve their fitness levels over time experience reduced mortality risk.
* Dose-Response Relationship
A dose-response pattern exists: as cardiorespiratory fitness increases, mortality risk decreases.
* Plausibility
Mechanisms underlying this association include improved cardiovascular function, enhanced metabolic health, and reduced inflammation. We know that regular exercise improves heart health, insulin sensitivity, lipid profiles, and overall physiological function.
* Coherence
The association aligns with existing knowledge about exercise physiology and health.
* Experiment
Although we cannot perform a randomized controlled trial where we randomly assign people to have higher VO2 max, observational studies provide strong evidence.
* Analogy
Analogously, we can draw from other well-established causal relationships. For example, the association between smoking and lung cancer was initially based on observational studies, and later experimental evidence confirmed the causal link.
The evidence (and my personal biases) would indicate that improving fitness is a cause of better health. I explain why this may be the case in my book.
If you donât know your VÌO2 max, I provide several methods to estimate VÌO2 max in my book, and for a limited time, I made this chapter open to everyone on my Substack. Feel free to look at some of the protocols and do some testing!
Regardless of your current fitness level, take comfort in knowing that improving your VÌO2 max by 1â3 METs (and reducing your risk of death and disease substantially) is very attainable with some dedicated aerobic exercise training.
Out of all of the risk factors, VÌO2 max is the one thatâs most fun to improve. It might also be the most important.
Thanks for reading. Iâll see you next Friday.
~Brady~
The VO2 Max Essentials eBook is your comprehensive guide to aerobic fitness, how to improve it, and its importance for health, performance, and longevity. Get your copy today and use code SUBSTACK20 at checkout for a 20% discount. You can also grab the Kindle eBook, paperback, or hardcover version on Amazon.
Examine.com: Examine is the largest database of nutrition and supplement information on the internet.
This is a public episode. If youâd like to discuss this with other subscribers or get access to bonus episodes, visit www.physiologicallyspeaking.com/subscribe -
Greetings!
Welcome to the Physiology Friday newsletter.
ICYMI
On Monday, I posted a video interview that I recorded with Aidan Chariton from Shortcut U. We discuss the importance of endurance training and other things related to human health and performance.
On Wednesday, I posted my â7 Rules for Health.â
Details about the sponsors of this newsletter including Examine.com and my book âVO2 Max Essentialsâ can be found at the end of the post!
Physiologically Speaking is a reader-supported publication. To receive new posts and support my work, consider becoming a free or paid subscriber.
"Drink, sir, is a great provoker of three things⊠nose-painting, sleep, and urine. Lechery, sir, it provokes, and unprovokes; it provokes the desire, but it takes away the performance." â 'Macbeth' (1606) act 2, scene. 3, l. [28]
Itâs clear that Shakespeare recognized alcoholâs role as an intoxicant, a somnogen, and a diuretic.
Though alcohol may be a âprovokerâ of good spirits and whimsy for a short while, its âunprovokingâ effects on sleep are well known to most.
Iâm not a teetotaler, but I recognize the harmful effects of alcohol abuse. Some people enjoy a few drinks on occasional while others wish to abstain. I support both decisions.
One often-cited reason for alcohol consumption is as a sleep aid â nearly 20% of adults in the United States say that they use alcohol for this purpose.
Thereâs one problem with this strategy. Although alcohol may help you fall asleep (itâs a depressant after all), it impairs your ability to stay asleep and worsens the quality of your sleep.
Iâve written on this subject before. Alcohol can elevate body temperature and heart rate, reduce heart-rate variability (HRV), and disrupt the regulation of our autonomic nervous system during sleep, all of which reduce the restorative quality of sleep.
In higher quantities, alcohol disrupts the normal architecture of our sleep â architecture referring to the time we spend in the various sleep stages (i.e., light sleep, rapid eye movement or REM, slow-wave sleep/deep sleep).
Alcohol also appears to cause more fragmented sleep, characterized by more wakefulness throughout the night. This may be due to the alcohol-induced increase in body temperature, an increased need to urinate owing to alcoholâs diuretic effect, apneic episodes during sleep (when we stop breathing), and the so-called ârebound effectâ that occurs when alcohol is metabolized, which leads to wakefulness due to blood glucose fluctuations, dehydration, and digestive discomfort.
All of these effects are well known to occur when alcohol is consumed in close proximity (e.g., 3 hours or less) to sleep and happen in a dose-dependent fashion. The more you drink and the closer to bedtime you drink, the more you disrupt your sleep.
What is less well-understood is how (or if) alcoholâs effects on sleep persist, worsen, or diminish over consecutive nights of alcohol consumption. Does our brain and body âhabituateâ to repeated drinking episodes or is it a downward spiral until we abstain?
Itâs also not known if the effects of alcohol on sleep architecture are consistent throughout the night. In other words, does alcohol affect sleep stages differently a few hours after bedtime compared to in the middle of your sleep period?
These questions were investigated in a new study published in the aptly named journal Sleep.
A total of 30 participants completed the study (15 men and 15 women with an average age of 33), none of whom had Alcohol Use Disorder but all of whom reported a moderate drinking habit (9â12 standard drinks per week for women and 12â15 standard drinks per week for men). An important consideration given that people who donât drink or who drink âtoo muchâ might have different responses to alcohol consumption.
The participants completed two 3-night experimental conditions in a random order. A washout period of 4 nights separated each condition.
In one condition, the participants consumed 3 standard drinks (targeting a breath alcohol concentration of 0.08) in 45 minutes. The last drink was about 1 hour before bedtime. If you're curious, the two choices were Everclear or vodka in some type of mixer. They did this for 3 nights in a row.
In the other condition, the participants drank just a mixer (no alcohol; this was the control condition) before bed. As in the alcohol condition, they did this for 3 nights in a row.
The participants also completed a standardization phase before the study. For 8 days, they maintained a regular sleep schedule at home (7.5â8.5 hours of sleep per night) and avoided recreational drugs and alcohol, sleep medications, and excessive caffeine (more than 360 mg per day or caffeine after 2 p.m.).
Overnight, brain activity and other physiological metrics were measured using a technique known as polysomnography (PSG). PSG allows for, among other things, the measurement of the time spent in various sleep stages, which for this study included slow-wave sleep (SWS) and rapid-eye-movement sleep (REM). Other outcomes included the total sleep time or sleep duration, the time spent awake each night, sleep latency (the time it takes to fall asleep), and wake after sleep onset (WASO; how much time you spend awake after falling asleep for the first time).
What made this study unique was the separation of each night into thirds, permitting a detailed insight into the specific âwindowsâ of sleep that were most affected by alcohol. This produced some interesting findings that Iâll expand on in the next section.
Results
As I discuss the results, keep in mind that in all cases, the specific nights or time points in the alcohol condition were compared to the average of all 3 nights or time points in the control condition.
On all 3 nights with alcohol, SWS increased during the first third of the night compared to the control condition but was lower during the second two-thirds of the night compared to the control condition.
On the other hand, REM sleep decreased on all 3 nights with alcohol compared to the control condition and also during the first third of the night (but not the second two-thirds).
Using a unique temporal analysis, the researchers identified many differences in the timeframes when the amount of time in the various sleep stages was different between the conditions.
The proportion of time spent in SWS was higher in the alcohol condition (vs. the control condition) between 1.8 and 6.5 hours after bedtime. This was consistent across all 3 nights, and indicates that the effects of alcohol on SWS are persistent.
The proportion of time spent in REM sleep was lower in the alcohol condition on night 1, specifically between 1.4 and 7.8 hours after sleep onset. On nights 2 and 3, REM sleep was lower between 2.1 and 5.3 hours after sleep onset. Put another way, the effects of alcohol on REM sleep diminished (occurred in a narrower time frame) with consecutive nights of alcohol consumption.
WASO was only higher on night 1 of alcohol consumption compared to the control condition, specifically from 5.6 hours after sleep onset until wake time.
There were also some notable differences between nights 1, 2, and 3 of alcohol consumption.
For one, the participants spent more time awake on alcohol night 1 vs. alcohol night 2 (from 1 to 2.7 hours after sleep onset) and on alcohol night 2 vs. night 3 (from 5.1 to 6.7 hours after sleep onset).
Second, WASO was different on alcohol night 1 vs. night 2 (from 5.2 hours after sleep onset until awake) and on night 1 vs. night 3 (from 5.4 hours after sleep onset until awake).
These results indicate a few things about the impact of consecutive nights of alcohol consumption on sleep:
Pre-sleep alcohol reduces SWS, effects that begin around 2 hours after going to sleep or right around the end of the first sleep cycle. These effects persist when alcohol is consumed for three nights in a row.
Consecutive nights of pre-sleep alcohol consumption decreases REM sleep, but these effects seem to be worse on the first night (an 11-minute decrease in total REM sleep) compared to the second and third nights (a 4-minute decrease in total REM sleep).
Alcohol seems to increase wakefulness in the later periods of sleep, from about 5 hours after sleep onset until the time you wake up.
The findings on REM sleep may indicate that the nervous system somehow adapts to these pre-sleep alcohol levels to ârescueâ time spent in REM sleep, but this doesnât happen for SWS.
REM sleep is where dreams occur. During REM, our brain activity, breathing, and heart rate and blood pressure increase. Our eyes also move back and forth rapidly, hence the name. REM sleep is thought to play an important role in memory and learning and likely had an important evolutionary role.
This doesnât mean SWS is any less important. SWS, also known as deep sleep, happens early in the night and is when the body relaxes into a period of restoration. This sleep stage is thought to play an important role in growth, memory, and immune function. Why SWS increases with alcohol consumption (at least in the early parts of sleep) isnât quite clear, but is probably related to alcoholâs depressant and inhibitory effects on the brain. This would make sense as levels of alcohol in the blood would be highest in the earlier parts of the night and decrease as sleep progresses.
How can you apply these findings?
Avoid alcohol close to bedtime.
In this study, the participantsâ pre-sleep breath alcohol levels were between 0.038 and 0.087 (the average was 0.066 or just below the legal limit) and they finished their last drink around 1 hour before bedtime. This is way too close for comfort if you want to avoid alcoholâs effects on sleep. Donât go to bed with alcohol in your system.
I think a minimum of 3 hours seems prudent. One alcoholic drink takes about an hour to metabolize and leave your system. So 3 drinks would require about 3 hours to metabolize, more or less. This is why I advocate day drinking (kidding, folks).
If you donât drink, then youâve got nothing to worry about.
Cheers, and thanks for reading. Iâll see you next Friday.
~Brady~
The VO2 Max Essentials eBook is your comprehensive guide to aerobic fitness, how to improve it, and its importance for health, performance, and longevity. Get your copy today and use code SUBSTACK20 at checkout for a 20% discount. You can also grab the Kindle eBook, paperback, or hardcover version on Amazon.
Examine.com: Examine is the largest database of nutrition and supplement information on the internet.
This is a public episode. If youâd like to discuss this with other subscribers or get access to bonus episodes, visit www.physiologicallyspeaking.com/subscribe -
Zijn er afleveringen die ontbreken?
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Greetings!
Today I'm releasing the first installment of an audience question and answer!
This Q&A includes questions that I've received throughout the previous month related to nutrition, health, science, my routines, my training, etc.
These are questions Iâve received from my Substack subscribers, people on X who may send me direct messages, or question Iâve received about things Iâve posted on social media or my blog.
Physiologically Speaking is a reader-supported publication. To receive new posts and support my work, consider becoming a free or paid subscriber.
For this Q&A, I took a sampling of questions that I would be able to expand upon and provide some more context about, but also things that I thought you all might find interesting to know the answers to.
If you enjoy this Q&A, I would love to make this a monthly thing and at some point, I may start to submit requests for questions from my audience.
For now, the Q&As will just be a compilation of random questions that I have received.
This Q&A will be free to all subscribers so you can get a taste of what future Q&As might look like.
Watch the video above or, if youâre so inclined, Iâve provided a (rough) draft of the questions and my responses below! You can also download/listen to the podcast on Apple Podcasts.
Alright, letâs get to your questions.
Brady, how useful do you find CGMs? I have used them on and off for a while, and I have very mixed feelings. Sometimes I think they make eating more difficult. (Peter) Attia and others don't think that one should exceed a blood glucose of 140. I'm not sure that makes sense.
Tl;dr: Continuous glucose monitors can be extremely insightful to use for a month or two, but unless you have diabetes or are at a high risk of having diabetes, itâs probably not something you need to use all the time. I learned a lot about my body and responses to food and exercise by using a CGM For a month.
CGM is referring to continuous glucose monitoring. These are or once were only available to individuals with diabetes as a way to manage their glucose control. CGMs are a device placed on the back of your arm. A little needle is inserted and it goes into your interstitial space and it measures not blood glucose, but rather interstitial glucose.
Nonetheless, it can give a 24-hour reading of your blood glucose concentrations. CGMs are a lot better to use than just say a snapshot of your blood glucose after a meal. They allow you to see what your blood glucose levels are doing throughout the day.
So how useful do I find that they are?
I think that everyone should probably use a CGM at least once for maybe two weeks to a month or maybe up to two months. I think they can be very valuable, perhaps invaluable tools for learning about how your body responds to certain foods, learning about how your body responds to exercise or sauna or different types of stresses, and even what your blood glucose levels look like before you go to sleep at night or while you're sleeping or when you wake up in the morning.
I think that using a CGM for a month or two could give you an insight into here's what happens to my blood glucose when I eat some french fries or here's what happens when I'm fasted or you know in the middle of a high-intensity workout.
I used a CGM for about two weeks maybe even more like a month and I learned some interesting things. The most interesting thing was that not a lot of things food-wise, I guess, raised my blood glucose as much as I thought they might, maybe due to my exercise levels or the fact that, I mean, generally I tend to eat fairly healthy even though I do, you know, eat some carbohydrates and sugar from time to time.
But I found that it was very useful. I learned a lot, but I don't know if it's something that I would always use because in a way it did seem to get in the way of, or I guess make eating a little bit more difficult. I think that CGMs may not be good for people who are prone to having an eating disorder or who have tendencies to maybe avoid foods just because they're going to elevate your blood glucose a little bit.
An increase in blood glucose in response to a meal is a normal physiological response. And of course, if you measure your glucose two hours after a meal and it's over 140 or near 200, that could be a sign that you might have diabetes. But if your glucose levels elevate to 120 in the 30 minutes after a meal and then start to decline, that's a normal response. That's what's going to happen when you eat something that contains carbohydrates and it's probably nothing to be scared of. I don't think that transient rises in blood glucose are dangerous per se.
So again, I think that using it all the time, may, at least for me, it would probably be a nuisance and kind of a burden because I would always just be paying attention to my blood glucose.
And I just don't think it's probably healthy, at least for someone like me in that case.
If you're worried about diabetes or diabetes runs in your family, or you're worried about metabolic issues, I think CGMs can be super valuable.
Regarding the last point on Attia and others, not thinking somebody should exceed 140, you know, I won't necessarily comment on that. I'm not a clinician, I'm not a physician, but again,
I think that, you know, elevations in blood glucose in an otherwise healthy person are just a normal response and they're not necessarily indicative of disease or underlying pathophysiology.
So short answer to that question is I'd recommend, you know, CGMs are becoming available over the counter. I think the FDA just approved the first one of those, so we're all going to be able to have access to it probably very soon. I would recommend that most people, you know, try one out for a month or two.
Brady, do you have a sense of which benefits of intermittent fasting or time-restricted eating arise from going a certain amount of hours without eating and which arise from having a certain amount of acute energy deficit? This is a practical/lifestyle question for many endurance athletes because if most of the benefits come from an energy deficit, then I could just do a long run or workout. bank a 1,000 to 2,000 deficit plus another from my resting metabolic rate, maybe skip breakfast and have a 3,000 calorie deficit by lunchtime.
Tl;dr: For weight loss, itâs all about the energy deficit. However, time-restricted eating may have unique benefits for metabolic health independent of weight loss.
I think a shorter version of this question is: Are there unique benefits to intermittent fasting independent of calorie restriction? Or is it all just about calorie restriction? Are all of the benefits just due to calorie restriction?
I think it's a little bit of both, but I also think that it depends on what your goals are.
When it comes to just weight loss, I think that it's all about your energy deficit and it's all about calories. This is evidenced by the fact that when we look at randomized controlled trials or meta-analyses of randomized controlled trials, comparing time-restricted eating versus a calorie-restricted diet that doesn't have time-restricted eating, both tend to result in similar amounts of weight loss. Neither of them seems to be better for weight loss.
Time-restricted eating does appear to be an effective way of reducing calories because when you limit the window in which you're able to eat, say to four to six hours during the day, you're probably just going to eat less naturally versus if you allowed yourself 10 to 12 hours to eat during the day, of course.
So for some, I think time-restricted eating represents this way to artificially or not artificially, but naturally reduce how many calories they're eating. But if you're trying to lose weight, it's all about just energy deficit and however you achieve that, you know, it's kind of up to you.
Where I think time-restricted eating may have unique benefits though is in terms of fat-burning ability, increasing mitochondrial content, mitochondrial enzymes, and improving your ability to burn fat.
I think that going, say, 10 to 12 hours per day, maybe even more, maybe 12 to 16 hours per day, doing that sort of a 16-8 time-restricted eating type of thing can be beneficial in its own right, independent of calories for certain metabolic benefits there. I think time-restricted eating can be great for that.
But again, if your goal is just to lose weight, there doesn't seem to be anything special about time-restricted eating.
What are your thoughts on following training plans by distance versus time? For example, a 7-, 9-, or 12-mile run in a training plan is very different for someone who averages 7 minutes per mile versus someone who averages 12 minutes per mile. So should the 10 to 12-minute miler be running the same distance or the same time?
Tl;dr: If youâre training to race a particular distance, basing your training on distance makes the most sense.
This is a great question. I think that overall, time should probably be a consideration maybe for someone who is just starting out. Say, you know, I want to increase the time that I'm running.
We use running in this case since that was used in the example.
I want to increase the time that I'm running per week from, you know, one hour to three hours.
But I think that I always like to train by distance and this would kind of be my
opinion just based on how I like to train but also I think it makes logical sense that if you're training for a particular race. Take somebody who's trained for a marathon I guess well that marathon is 26 miles so you're going to want to train yourself to be able to run 26 miles. And so obviously you could just train by time and not think about miles.
But in my opinion, you want to probably base your training on mileage run for the week. So I want to run 30 miles this week or I want to run 40 miles this week or get a 20-mile long run in.
If you tell two runners training for a marathon to run 3 hours in a week, the person who's running the 7-minute miles is going to get a lot more miles covered in that time than the 12-minute miler. I think training by miles is probably better and makes more sense.
If you're training for a distance, I think prescribing your training based on distances kind of makes the most sense there.
Do you usually run early in the morning? And if so, do you eat a very carb-heavy dinner?
Tl;dr: I run at 5:30 in the morning every day and donât eat beforehand. The dinner the night before is usually substantial, but not purposefully more âcarb-heavyâ than the other meals during the day.
I do run very early in the morning on the weekdays and typically on the weekends too, although I do sometimes sleep in for maybe one to two hours extra on the weekend because I have a little bit more time.
During the week, I typically wake up around 4:45. So my alarm is actually for 4:43. Don't ask me why. It's just random and I chose that time.
But I'm usually out the door for my run by about 5:30 on Monday through Friday it might not always be a run it might be a bike but I'm working out at 5:30 in the morning during the weekday almost every morning so I don't eat anything before those sessions. That's just due to mostly logistics not necessarily a reason that I'm like trying to do those workouts fasted. I don't have enough time to wake up and eat breakfast and let it digest before I go and run.
I'm typically not running or riding maybe for more than like two or two and a half hours. And if the workout is of a low enough intensity, I probably don't need to eat anything. So I'm usually just doing those workouts fasted. But I will have a pretty substantial dinner the night before.
We typically eat dinner around 6, and finish sometime around 7. 7:30 is kind of when I have my last bite of food during the day.
Is it carb-heavy?
It's not more carb-heavy than usual. Dinner usually is the meal of the day that has more carbs than the other two meals like breakfast or lunch, but I don't necessarily make it a point to stuff myself with carbs during that dinner. I just have a normal dinner and that tends to carry me through the workout the next morning. Sometimes I'll put honey in my coffee if it's like a workout in the morning and that tends to help as well with a little bit of the energy issues there.
How do you exactly record walking? Do you go out for a specific walking session or do you record every time you walk?
Tl;dr: If I go on a walk for the sole purpose of going on a walk, Iâll log it using my GPS watch just like I would a normal activity. I like to quantify all of my purposeful activity during the week and typically log about 4â5 hours of walking per week.
This I believe is about, typically I'll post like a screenshot of my weekly activity, including my running, my biking, sometimes strength training, and how much I'm walking during the week.
So I'd like to, it's something I've recently started doing.
I recently only logged my formal workouts. So if I go on a run or if I go on a bike ride, I'll log that on my GPS watch. Walking was kind of just something that I did and didn't log, but recently I've been going on dedicated walks.
So I'll take my son in the stroller and sometimes my dog too and go out on walks for 30, 45, or 60 minutes sometimes if it's nice out and I have some time to spare.
I have been logging those recently because I figure it's a kind of training and I would like to see how much walking, how much purposeful walking I'm doing during the week. So I log all of my walks.
If it's going to be like 15 minutes or more and I'm going on the walk for the sake of the walk, I will log it. If I'm just, you know, going out to take my dog around the block maybe for a few minutes I'm not necessarily going to log that so purposeful walks I log all of those and count that kind of in addition to my other training that I do. Again, this is something that I've recently just been doing to try to quantify all the stuff that's going on during the week and I found that to be pretty fun.
Have you ever had a full thyroid and hormonal panel done? For example, cortisol. If I start approaching more than 10 miles in a week, my sleep goes to sh*t. I typically lift three times a week too.
Tl;dr: The more I train, the better I tend to sleep unless Iâm training too hard and risk overtraining. Working out at night can sometimes negatively impact my sleep unless Iâm able to cool down my body beforehand. I try to avoid working out too late and doing high-intensity training too close to bed.
I sleep like a baby.
Recently I've been training a lot and we have an almost one-year-old son in the house so by the end of the day I'm typically just exhausted along with working during the day.
I never have had sleep issues. I've always slept pretty good.
There are some certain circumstances though where I think sleep has maybe been affected by training. One of those instances would be, say, perhaps during the summer or if I'm increasing my mileage a lot and I may be overreaching a bit and maybe in a bit of sympathetic overdrive, perhaps combined with maybe not eating enough, that can typically lead to my sleep being less than ideal, I have found.
The second time when my sleep might suffer is if I time my exercise too late in the afternoon or make it too high intensity, and then it's too close to sleep, that can typically interfere with sleep as well. If I finish that workout before like 6:00, typically, and don't eat an insanely big dinner afterward, sleep is typically fine, as long as I can get my body temperature back down to normal.
If I do a high-intensity workout and it's a bit later in the evening than I would like, and you eat a big dinner and you're trying to go to bed, you're hot, you're kind of over-activated, your heart rate hasn't come down yet. That tends to make sleep bad as well.
But regarding just overall training, I mean, the more I train, the more I tend to want to sleep and to think the more sleep that I need. So no, I've never had sleep issues.
I never really had a thyroid and hormone panel done either. I mean, I've had some blood work done in the past, but I don't remember specific numbers or anything for that, but is probably something that I should do. Maybe a yearly test might be something that's probably valuable for me to do and something that I will look into but regarding strategies, maybe, you know, if you are training hard and are suffering or having a hard time sleeping.
I think the best strategy you could do is to try to work out in the morning if you can if you're not already doing that. So evening workouts could be affecting your sleep.
The best thing that I can do to improve my sleep after a workout is to get my body temperature as low or back as close to baseline as possible before I go to sleep.
So if I do an evening workout, if it's cool outside, if it's the spring, go on a little walk outside, maybe without a shirt or in minimal clothing, just to like cool down your body temperature because a high body temperature is going to be one of the main things that influences how well you sleep and how easily you're able to get to sleep, how easily you can stay asleep, and like the quality of that sleep.
So that's the biggest thing that I think will interfere with sleep, especially, you know, with the summer coming. Try to find some strategies to cool down, not just a physiological cooldown, but, you know, cool down your body after your workout. And I think that that will hopefully help with sleep.
Do you follow an 80-20 routine with a bike? I would like to add this to my running more. And do you find programming your week ahead of time works best for you?
Tl;dr: I bike about twice as much (time-wise) as I run during the week. Right now I bike for about 6â8 hours and run for 3â4 hours. The bike has helped me increase my exercise volume and fitness as a runner. Programming my week(s) ahead of time is something Iâve recently started being more diligent about and has been wonderful for training progression and avoiding injury.
So this is about how I split up my week, how I do a majority of my endurance training, splitting it between the bike, which is mostly on the indoor trainer, and running, which is outside.
I guess it tends to probably fall to around 80-20. I would say maybe it's more like a 60-40 kind of split, or like maybe a two-to-one ratio of biking to running.
So right now, I'm doing probably seven to eight hours of bike riding per week. And then running tends to be about four hours now, hoping to increase that a little bit in the future.
And that's intentional. I mean, I would like to run a little bit more, but struggling with injuries in the past few years has just made me change my tune a little bit on how I approach training and getting the volume per week that I want without, you know, increasing the impact. And that has led me to find the bike. I'm able to improve my fitness a lot by biking.
And so I would recommend that all runners, you know, you don't need to do a majority of your training on the bike. But if you're like me and maybe struggle with injuries at higher volumes and want to find a way to exercise a bit more without, you know, just running, I think the bike is great. I would recommend all runners bike.
I think that you know, currently I'm training for a marathon, and just running three days a week or four days a week, even for like 30, 40 miles, isn't going to cut it. Biking is allowing me to get that extra volume, the metabolic work that I need to kind of train for a marathon.
I'm curious to see how the race turns out when I'm able to, you know, with this training that I'm doing right now.
So yes, I do kind of follow an 80-20 routine, but again, that will just depend on what kind of volume of running that I'm doing. Typically, if run volume goes up a little bit, naturally bike volume is going to to fall a little bit.
In reference to programming my week ahead of time the answer to that would be definitely yes. Itâs not something that I have done a lot of in the past. I've been a runner like my entire life and so I tend to just fall back on kind of training um training tendencies and protocols that I have used in the past regarding like how the week is structured and what workouts you're going to use and how much I want to run during a particular week. It all has tended to be the same and I just have tended to do what works.
I've kind of just done my own thing and been my own coach, but I haven't done much coaching for myself rather than just, you know, kind of go with the flow in terms of training.
But now in the past month or this year, I guess, is when I started to formally sit down and plan out some more structured training for myself.
Sometimes that involves planning something 8 to 10 weeks out, but more often than not, it's like, let's just sit down and look at what the next month looks like. What does my fitness look like? Where am I in training? What kind of volume can I do? Am I training for a race?
And then just plan out the next month.
I think I find that valuable, not only because it kind of prevents me from doing maybe too much or not doing enough and like getting the right workouts in, but also because it just offers a lot of psychological flexibility and that you don't have to wake up every morning and figure out what to do or plan your workout for the day. It's already there.
And so this can be something, again, as simple as like Sunday night, typically I'll just sit down and write in my planner what I'm doing Monday through Sunday this next week. That just frees up a lot of psychological space as well and gives me a little bit of confidence going into the week that, I know, you know, these times are set aside for working out.
I know what workouts I have to do to get where I want to be at the end of this week. So yes, it's a great thing to do. Program your week ahead of time.
It doesn't have to be 8 to 10 weeks in advance, but I would recommend everybody on Sunday or Saturday, depending on when your week starts, sit down and do some sort of semi-structured plan for the week. It can be very helpful.
How do you titrate running volume coming off injuries?
Tl;dr: I typically start by running 3 days per week or running every other day for a few months. Iâll add 5â10 minutes to each run every 2 weeks, and eventually add another day of running. Itâs always a combined progression of volume and intensity.
Progression of running coming off of an injury is, is always hard and everyone will have unique situations based on what your injury was and how much time you took off.
So most recently, and I think this question was about my most recent injury was a stress reaction in my femur that forced me to take, uh, about a month off of running.
So I took a month off. I was still able to cycle during that time and do some strength training.
So it wasn't, you know, a completely one month of inactivity.
I was able to, I think, maintain some strength and fitness. But when I came back from that, you know, what I typically do is just I'll run every other day. And I will kind of start at the minimum dose of running that's at least somewhat substantial.
So I did my first run back was 30 minutes. I did another 30-minute run on Wednesday. So I ran 30 minutes on Monday, and 30 on Wednesday. On Saturday, I did a 45-minute run, I think.
Again, that might be a lot for some, and even for me coming back from some injuries, but this one was different. I don't think I had lost a lot of fitness, so I was able to kind of start at a higher baseline than previously.
But run three days a week. So control running frequency. Don't go running every day during the week when you first come back.
And then obviously intensity. I don't do workouts for like a month for when I'm first coming back. I just do a lot of like easy running.
And then obviously volume.
So the way that I like to progress is to do two weeks of the same amount of volume and then kind of step up every two weeks. So that will pretty much include adding 5 to 10 minutes to every run. And that ends up just, you know, increasing your overall weekly volume by maybe 30 minutes to 45 minutes or something like that. And that tends to be like a safe progression for me.
I know that sometimes people will recommend that you donât increase by more than 10% per week.
If you're running volume is very low, you know, I think you can probably go beyond that and maybe go up to even like 20% per week.
But again, your mileage, uh, your mileage may vary on that one, but progression is always the key and slow conservative progression, even though it's hard, you know, especially for me, especially I have a hard time progressing with the running. When I come back, you get excited. You want to run a lot, but, um, just being patient is important.
Do you ever do post-run glucose levels?
Tl;dr: I have a glucose monitor and if Iâm curious, Iâll measure my glucose levels during the day or after a run, but not normally. Itâs not something Iâm too concerned about.
So do I measure my glucose levels after I run? This kind of is in relation to our first question on continuous glucose monitors.
I don't typically.
I do have a glucose monitor at home. It also doubles as a ketone monitor, which is kind of interesting. I'll measure it from time to time if I'm curious. If something feels off, I'll measure it.
If I'm just curious, like if I've maybe fasted for a long time and did a particularly long run, I will measure my glucose levels, but more often than not, I'm not typically worried about it.
That's an instance where I think a CGM would be fun and handy to have, you know, what are my glucose levels during a run? What do they look like after, you know, if they're too low, maybe you need to, you know, add more carbs to like your post-workout meal or something like that.
But, um, so that the answer to that would be, no, I don't, I don't find a need to, but I will do it in special cases if I'm curious or if something seems amiss and I think measuring glucose levels might provide some useful information or something like that.
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Dr. Elisabeth Bik is a microbiome scientist. She received her PhD from Utrecht University in the Netherlands. Her scientific work has included time at the Dutch National Institute for Health and the Stanford University School of Medicine.
She previously worked as a science editor and scientific and editorial director at uBiome, and director of science at Astarte Medical.
Currently, Dr. Bik has transitioned full time to a Microbiome and Science Integrity Consultant. Her work has been featured in major news publications including Nature, the New York Times, the Washington post, le Monde, The Scientist, and more. She often shares her detective work on social media, where she has nearly 150,000 X followers.
Sheâs doing important work and I was honored that she agreed to come on the podcast to talk about some of it.
This is a public episode. If youâd like to discuss this with other subscribers or get access to bonus episodes, visit www.physiologicallyspeaking.com/subscribe -
You can also find this podcast episode on Apple Podcasts.
Dr. Tamara Hew-Butler (@hyponaqueen) is a podiatric physician and associate professor of Exercise and Sports Science at Wayne State University. She earned her PhD at the University of Cape Town, South Africa, where she studied and trained under the legendary sports scientist and physician Dr. Timothy Noakes. Dr. Hew-Butler is a Fellow of the American College of Sports Medicine (FACSM) and specializes in both sports medicine and exercise physiology. Her expertise is in exercise-associated hyponatremia, a topic we cover in detail, and the hormonal regulation of water and sodium balance. She is also an avid runner.
I reached out to Dr. Hew-Butler after reading a cover story on her that appeared in the Physiologist Magazine, which is a monthly publication from the American Physiological Society.
After reading this story, I immediately contacted Dr. Hew-Butler to invite her on the podcast, because I knew sheâd make for a fascinating guest. Given my recent interests in talking about and often debating hydration and water drinking on social media, this seemed like a perfect opportunity to interview someone with expertise on all things hydration who has both field and laboratory experience on the topic. In fact, her interest in the topic first began when she was part of the race staff at major road races and observed cases of athletes experiencing sometimes near-fatal cases of âoverhydration.â
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This is a free preview of a paid episode. To hear more, visit www.physiologicallyspeaking.com
Greetings!
Today, Iâm (re)releasing a conversation I had with Dr. Brad Stanfield. This was initially an episode of my podcast, but now this is the only place youâll find it.
We talk about what âlongevityâ means, research on diet, supplements, and exercise for longevity, and controversies in the longevity field. See below for Dr. Stanfieldâs bio.
Enjoy.
PhysâŠ
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This is a free preview of a paid episode. To hear more, visit www.physiologicallyspeaking.com
Authorâs note: the first 45 minutes of this episode is a discussion between myself and Dr. Vincent about results of my gait analysis. Skip to 45 minutes if you donât want to listen to this and prefer to hear about healthy running habits and footwear.
Dr. Heather Vincent is the Director of Research and Director of the the UF Health Sports Performance CentâŠ
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This is a free preview of a paid episode. To hear more, visit www.physiologicallyspeaking.com
Dr. Howard Luks is a board-certified orthopedic surgeon, chief of sports medicine and arthroscopy, and assistant professor of orthopedic surgery at New York Medical College. Dr. Luks's focus is on injuries that involve the shoulder, knee, ankle, and elbow. You can find him on X at the handle @hjluks.
In addition to his expertise in sports medicine, Dr. LâŠ
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Joseph Watso, PhD, is an Assistant Professor in the Department of Nutrition & Integrative Physiology at Florida State University. Joe directs the Cardiovascular & Applied Physiology (CAP) Laboratory which has the mission to advance knowledge on cardiovascular disease prevention and treatment strategies. His research interests include the role of lifestyâŠ
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This is a free preview of a paid episode. To hear more, visit www.physiologicallyspeaking.com
This interview originally appeared on my (now âdefunctâ) Science & Chill podcast on November 1, 2022. Now, itâs only available to Physiologically Speaking subscribers.
Iâll be posting videos twice per month. Be sure to subscribe, because thereâs some stellar information in these interviews!
Enjoy!
