Hey after this episode first came out we head from some scientists in the field that we had missed some research about exercise and depression. They were right. We are sorry about the oversight and we've updated this part of the episode to reflect the most current research on the topic. Ok.. on with the show…
Hi I’m Wendy Zukerman and and your listening to Science Vs from Gimlet. We are back for a brand new season… On today’s show we’re pitting facts against getting physical. As we look at Exercise… is it like a blockbuster drug or ballbusting drag?
So it is a beautiful Sunday, Brooklyn, NYC, and I am heading to the park, my local park to see why people do exercise…
All around me people were sweating their butt off... and when I asked them WHY there was one reason that came up again and again[1]…
To look good obviously… Not have like a beer belly ‘n stuff
To shed it! Shed it all!
Too look good naked, so. Who are we kidding here, yes!
But this isn’t just about looking good in the nud… people had all sorts of ideas about the power of exercise… they talked about it like it was some kind of miracle drug…
It is a medicine! It is a medicine.
It helps me reduce stress, absolutely, if not I'm ready to snap on someone so...
Decreases the chance of cancer
I think definitely decrease risk of heart attack
Definitely making me feel like i should be running instead of asking questions
On today’s episode we are going to find out which of these things exercise can do and which it can’t . Because I’ll tell ya - some of the things you think exercise works for - it doesn’t.
When it comes to exercise… a lot of people want
To look good naked…
… but then there’s science…
AHHHH
Science Vs Exercise is coming up… after the break
BREAK
Welcome back… to today’s show on Exercise! First up we're tackling whether Exercise can help you lose weight. Since the 70s[2] we’ve had peppy spandex clad heroes telling us the best way to lose weight is to exercise.
Let’s sweat again! Come on everyone
Yep… you want the perfect bod? Keep on sweating...
Circle those hips, the bigger the circle the thinner the waist!
Well I’m here to tell you… that Jazzercise lied to you.
YF Yeah so people can lose weight with exercise, it’s just that they tend not to lose weight with exercise.
This is Dr Yoni Freedhoff[3] ... He helps people manage their weight at the Bariatric Medical Institute in Canada… it’s Yoni’s job to keep up with the latest research related to weight loss and he says that when it comes to exercise the evidence is clear… it is not the weight loss pill that we’ve been promised. Like, he told me about this one study…
So this was a really impressive study. Basically what they did is, they took sedentary, between the ages of 40 to 75.[4]
The researchers got around 200[5] people who barely worked out. And half of them were told to exercise....and we’re not talking some walk among the petunias here… we’re talking vigorous exercise - like running or biking… And these people did it for roughly an hour … for 5 days a week on average…for a year.
An hour a day!?
Yeah this is not a small amount of exercise, and some of this exercise was also observed
Yeah… the researchers actually watched them to make sure they were exercising[6] … …they also gave them pedometers[7], and made them fill out diaries.
What they found that yes the exercisers did lose some weight, perhaps a lot less weight than people would expect.
So. Vigorous exercise. An hour a day. 5 days a week. For a year… woof! I would expect you'd lose like 20 lbs/ 10 kilos… or something right? So… what did they find?
The women lost 1.4 kilograms[8], so for American listeners that’s in the neighbourhood of 3 pounds.
And the men in the study lost around 4 pounds…. That’s it… and many, many studies have found basically the same thing. [9] [10] . [11] [12] The evidence here is weighty. It's really hard to lose weight by just doing exercise… And if you still don't believe me... Yoni told me about another study that tracked people for ten years
This is a good one… so this is the Doetinchem study.[13]
How much did you practice saying deutenchem?
I googled it! Hahahahahahaha
Um and you know being jewish the chem is easy too.
Great.
So the Deutenchem study, they looked at 5000 adults for a decade[14].
The researchers checked in on the Deutenchemers to see how much exercise everyone was doing… and… they measured their weight and then at end of 10 years…they looked at the people who worked out a lot… and those who barely worked out and there was a lot of …
Unexciting data. So what was unexciting about their data was that Everybody gained weight!![15]
There was no statistically significant difference between the people who worked out more and those who didn’t. And if you’re thinking - maybe the numbers on the scale aren’t going down - because these people are adding muscle - Yoni says that it’s not so simple…
It's a myth that people who are not losing weight in the gym, because they're gaining muscle,
While Yoni says it's possible to gain a lot of weight in muscle if you do a ton of lifting weights,[16] and eating protein[17][18], people doing the casual workout, we just don't gain that much weight.
For those who exercise regularly, especially people who lift weights, to build 10, 15 pounds of muscle, that’s a lot of consistent work in a gym. That’s not something that happens quickly.
So face it. For most of us, exercise is not a good way to lose a lot of weight.[19] And why is this? Well there a couple of reasons -- number one --- even though we use up calories when we “circle those hips,” we just don’t lose that much. [20][21]
How long would it take me to burn of a bagel on a treadmill?
I would expect someone who's eating 300-400 calories worth of a bagel, that has a shmear of something on it - at least 40 minutes on the treadmill. [22] on a good clip… to see those calories disappear.
And there’s another problem here... studies have found… that when people think they have burnt a ton of calories from working out …. some people reward themselves by eating a bunch MORE calories.[23][24][25].[26] [27] [28][29] Like, One survey of more than 250 undergrads found that around 40 percent admitted to often or always eating more on their exercise days[30]… …You put it all together… and for many of us… it’s just so unrealistic… that exercise could help us shed a lot of pounds. So, why do we have it in our heads that it can?
It feels right! There's truthiness to it! Right? We're sweating, we’re moving! Our hearts are beating. It feels like it should help, I think that we do fool ourselves into thinking it’s having a greater impact that it might actually be having on us.
Losing weight is pretty much about.. what we put in.. to our mouths[31]…
When it comes to weight, I think it would be very difficult to outrun a bad diet, especially in the long term.
Conclusion. Exercise is not a good way to lose weight.
But don’t throw out your fancy athleisure wear just yet! Not that you were using it for exercise anyway … the thing is… even if exercise isn’t great for dropping pounds… doesn’t mean it can’t turn your day around?…Y’know make you feel good. And that takes us to our next question: Can exercise improve your mood?
DEPRESSION
We talked Gary Cooney about this. He’s a psychiatrist at Forth Valley Royal Hospital in Scotland
Yeah, I think like a lot of people it must be good for your mental health, when I go for a wee run or something, I feel like I’ve got some sort of positive benefits out of it, in my mood, yeah it definitely makes a difference to me.
A lot of runners, like Gary, say they feel good after a jog. And there are studies that back up this idea. They suggest that exercise can improve healthy people’s mood soon after they work out[32],[33][34][35] …
But researchers are taking this idea even further and looking at whether exercise can treat those who have clinical depression. Several years ago, Gary wanted to know if this was true. A lot of the patients he sees in his job have severe depression. And he said he’d love to have some more treatments in his arsenal. So he joined a team and dove into the research.
So we were gathering all the papers we could find, all the evidence could find that answers, is exercise beneficial to people with depression?
Gary was doing all this to create what’s called a Cochrane review…these kinds of reviews try to use only really good quality evidence… so we here at Science Vs we LOVE cochrane reviews…we do Jazzercise to them…. <<THE BIGGER THE COCHRANE REVIEW THE BETTER THE EVIDENCE>> Like with Gary’s review?
They chucked out the trials that went for less than a week[36]… OR… . where it wasn’t clear that the participants actually had depression[37]… and after Gary had his way with scores of studies… 6 were left standing… involving around 450 people!! … When it came to relieving depression… there was no statistically significant difference between people who exercised and those who didn’t.[38][39].
You know this one line a read once - you're only one run away from a good mood, and I just think that's so simplistic. And it’s just not true for people with severe depression.
So Gary’s work - and others - [40] have found that exercise isn’t a reliable treatment for depression [41][42] -- but even though that is true… there are some people in these good quality studies who DO report feeling a lot better after exercising. It just wasn’t across the board[43]… So, given this I asked Gary what does he tell his patients...?
[UPDATE 10/31/19 See citation 44][44]
Since Gary’s study came out there have been a few new clinical trials[45] [46] that have showed that exercise can help people with depression. And one reason that these newer studies might be finding a benefit is that these scientists were really tenacious about getting people to do the exercise[47]. Like in one study researchers gave participants free gym memberships and personal trainers - who hounded them if they don’t show up[48]….. And with all this, they did see a benefit. People reported feeling better.[49] I asked Gary what he tells his patients
It's worth pursuing, it’s worth trying, it’s worth seeing if it brings you any benefit, but we are working with a complex organ the brain, and it doesn’t give up its secrets easily. And we're not able to shout from the rooftops, about this being the panacea we’d hoped it would be. But I would still do it. If I was depressed I would see what I could do with exercise.. I think
Give it a go
Give it a go, I think so.
Conclusion. We don’t have great evidence that shows exercise can help with depression. . But if you’re struggling, it’s worth giving it a go.
After the break… the amazing things that exercise can do… and I’m not exaggerating, it can help protect you from the biggest killers around…
Conclusion. Some evidence suggests exercise helps with depression. So it’s worth giving it a go.
After the break… how exercise can help protect you from the biggest killers around…
BREAK
Welcome back… So we just found out that exercise is not a miracle weight loss drug… and as for the evidence that it can cure depression? Well, it’s a bit of a stretch… But now get your running shoes on… because there are all these amazing things that exercise can do for your body. Like - it can help protect you from the biggest killer in the United States[50]: KILLER bees. JOKES! Heart disease[51][52][53].
Back in the 1950s…research showed the very first link between exercise and heart disease… In a study of bus conductors on London’s big double decker buses[54]. -- researchers found that . conductors who would run up and down the stairs on the bus hassling people to buy tickets . Had half as many heart attacks as bus drivers - who basically sat on their bottoms all day…[55].
And over the next few decades [56]. [57] [58].[59] … more and more research showed that exercise could prevent heart disease[60][61].... possibly because going for a run can trigger the release of chemicals[62] - which reduce inflammation in your blood vessels[63] [64].[65] Ok. So exercise can help protect your heart. But now… researchers are learning that exercise might also protect your brain. To find out more…we spoke with professor of neuroscience, from NYU, Wendy Suzuki.[66]
How many wendy's have you met?
Not very many! There’s very few of us around! It’s a great name!
Orright, orright… So, several years ago, Wendy… number 2… was studying neuroplasticity… this idea that the brain changes itself…that was her main focus until she went on a rafting trip where she unhappily found herself to be the weakest person..
There were over 60 year old but they were much stronger than me, I was like what is the matter with me. Oh my god this is so bad, that's what made me go back to the gym.
Wendy wanted to get strong. So she went to the gym. Started working out… and she noticed something she wasn’t expecting… something to do with her brain… she thought that maybe her memory and focus were better after she worked out… Wendy couldn’t help but wonder… could exercise really be doing this?
Oh… I wonder if that's it, that's the seed and I thought, I totally want to study this!
She raced to the research and found evidence suggesting that, soon after people do aerobic exercise, like biking or running[67][68][69]… their focus and attention does improve a little bit[70] [71] … But what got Wendy really excited was the research she found on what exercise might be doing for her brain in the long term. You see… there is intriguing research suggesting that exercise could play a powerful role in protecting us from dementia. So for example, Wendy told us about a study - published just last year[72] [73], which had been tracking almost 200 women since the 1960s…
They were middle age, and asked whether they were low fit, mid fit, or high fit.
So, when the researchers started this study, they measured the women’s fitness on an exercise bike[74][75]…as a kind of proxy for how much exercise they were doing.
44 years later they came back, they found all these women and asked how many developed dementia?[76]
And what they found was pretty remarkable… [77] especially when they zoomed in on people who exercised the most.
If you were high fit you were 90% less likely to have developed dementia. High fit
WZ woah 90% less!
It’s huge[78]
Other research has found that on average, for people working out, you see a number closer to 40%[79]. [80][81][82]… [83][84]. [85] Which would still be very impressive. If regular exercise made you 40% less likely to have dementia. But there’s a hurdle here.
Some really important work here that still needs to be done to make sure that exercise is the thing that’s causing a drop in dementia. Because a lot of these studies[86] that has been done they’re survey based -- so researchers ask people -- how much do you work out and then track if they get dementia … and this means what we’ve got here is a correlation…between exercise and not having dementia…and it could still be something else about these fit people that’s protecting their brain. After all you’ve got to remember that old Jazzercise adage -
5, 6, 7, 8 The bigger the correlation doesn’t mean the better the causation!
To know if exercise is protecting us from dementia… we really need long term clinical trials… where scientists randomly pick people to do exercise for decades, and see what happens.. [87] And right now we don’t have those trials.
But before you say “well jog on then!”… one thing that might help us get closer to trusting this link between exercise and dementia... is if scientists knew how exercise could theoretically protect the brain… and there is one very cool idea - that is getting a bit of attention... it’s from research in mice, and it’s this.
Exercise literally stimulates the birth of brand new brain cells.
In rodents, running triggers the release of what are called “Growth Factors”[88][89] and they stimulate the birth of baby brain cells. So for example, scientists give mice a running wheel - and turns out… some mice loooove running… so they run and run and run… then scientist slice open their brain… and they see brand new brain cells. [90][91][92]
They can visualise these new cells. They can tell where the brain cells are are being born, And they can even look at the connections that these new brain cells make once they're born.
Wendy says this is all happening in a very particular area of the brain called the hippocampus.. Which is known to be important for memory… [93][94] And we do have intriguing trials in people - humans! - that show that after we do exercise we do see changes to parts of our hippocampus [95][96][97] [98]... So, the idea here is that… perhaps new brain cells in the hippocampus, born thanks to exercise, make our brain more resilient to aging…
So imagine every single time you work out, there's a shiny new hippocampal cell that gets born, ok it's not that quick, but that's the image I use to motivate me to work out, because I want as many shiny new hippocampal cells in my brain as I can get over my lifetime.
Without slicing open Wendy’s brain… we can’t actually see if she’s getting shiny new hippocampal cells from exercise[99] [100]… and we need more research to know if exercise can get all the credit for the lower rates of dementia.
Oh We're absolutely still working out the details to understand all these different complex things that happen with exercise on the brain…
But this hasn’t stopped Wendy from becoming a true exercise believer. While studying the effect of exercise on the brain… she even got trained to be a gym instructor… and she has this little ditty she shares with her classes…
I exercise to change my brain, Because I want it, I want it, I want a stronger brain! Yeah!
Nerd.
Conclusion: There is some exciting new work suggesting that exercise could protect our brain in the future by cooking up new brand brain cells.
And the final thing we talk about is exercise’s effect on the second biggest killer in the United States[101].... Quicksand! No! Cancer. Now I know I know, on this show we always hear people claim this or that can protect against cancer and we almost always say -- yeah not so much evidence bud -- but this time it's different. So, is there a link between exercise and lower rates of cancer?
YES, the short answer is yes.
This is Stacey Kenfield…at the University of California in San Francisco[102]...
There are many studies that have been published over the last few decades[103][104][105] showing that exercise reduces your risk of getting cancer.
WZ: That is, like I had no idea[106]
Yeah I think, overall people don't know about the relationship between exercise and cancer
Exercise is linked to a lower risk for getting many kinds of cancers[107][108][109][110][111] … and the strongest evidence is for colon[112][113], breast[114][115] and endometrial cancer. [116][117] Studies have found that on average people who regularly exercised were 20% less likely to get colon cancer and 10% less likely to get some kinds of breast cancer[118]. That’s according to a big report from the World Cancer Research Fund…
And another reason that we think exercise might help us fight cancer, is that scientists are seeing benefits in people who ALREADY HAVE cancer[119]. So several years ago, Stacy and her team did one of the first studies looking at this. They looked at more than two thousand men, who had prostate cancer. And her team followed them for almost 20 years[120]
Men who were doing three or more hours of vigorous exercise per week had a 61%[121][122] lower risk of dying of prostate cancer, and that number is just huge.
WZ: When you saw that number, what's going through your mind at that point?
So initially I was the one seeing the data for the first time. It was just really shocking that the benefit of exercise was so great
Other research - in some other cancers has found this too. That doing exercise, even if you have a cancer diagnoses, might help[123][124][125].[126] [127] Now a lot of these studies that’s we’re talking about also suffer from that correlation causation problem we saw in dementia so it’s important to try to figure out what COULD be the mechanism here. [128] Like how could a swim protect you from cancer? Well… there are a bunch of mechanisms that might be at play[129][130]… But one idea is that exercise could actually kill cancer cells.[131] You see there’s evidence that exercise can unleash these cells called “natural killer cells” [132]... [133]… and they can get into tumours. Stacey sent me a study[134] in mice who had cancer[135].... The researchers in that study got their mice to run and run and run[136]… and then they looked at their tumours under a microscope…
You can see the infiltration of natural killer cells in the tissue.
Oh wow.
But in the mice that didn't exercise? There were waaay less natural killer cells in their tumours[137] And once these “Natural Killer Cells”[138] are inside the cancer. They don’t mess around… after all they’re not called Natural Flower Cells.
Once a natural killer identifies the cancer cell it decides to kill it[139] and it releases chemicals that cause that cell explode! Or rupture[140]
That’s so cool.. I mean I know there’s lots of potential mechanisms, but this one is particularly cool
Yeah I think it’s really great.
When you're running at like full speed are you thinking about like… get those cancer cells?
I think about it a lot when I'm exercising! Really? I think it's like your body is reacting to exercise, all of these systems are working for you, I picture your body working for you, like an army to help you combat disease
WZ: pretty cool
Conclusion: There’s some good research suggesting that exercise can help you fight cancer, and it also might make it less likely that you'll get cancer in the first place.
So when it comes to Exercise… what’s it really good for?
Y’know, Exercise has benefits to truly almost every other chronic conditions… arthritis[145], cardiovascular fitness[146], it improves quality of life[147], it improves sleep[148], it improves pain[149]!
This is Dr Yoni Freedhoff again who told us that exercise is not good for weight loss… despite this… he is pretty much exercise’s biggest fan.
It really is a magical thing what sustainable exercise will do! If you’re growing older and you want to remain functionally independent… you want to be older wiping your own parts for longer! I mean these are things that are remarkable important to our lives, but these get short changed we just talk in regard to exercise is weight loss. If you were to ask me what is the single healthiest behaviour a person could undertake in the name of health - it would be exercise.
So maybe forget about exercise for shedding a bunch of weight… and start thinking about it as doing so much more…
That’s Science Vs Exercise…
C’MON EVERYBODY LET’S SCIENCE AGAIN
CREDITS
This episode has more than 140 citations!! And if you want to see them, you can clink on the link in our show notes or go to ScienceVs.show and follow the links to get to the transcript. Next week we are taking on America's favorite sport.[150]..football. And we’re asking how dangerous is it?
Grunt, That’s what I’ve been dreaming about since I was a little kid, since I was 5 years old, I want to be in the NFL! It makes you smile really broad. Yes, I was thinking if all of that happens how great my life would be.
This episode was produced by Wendy Zukerman, with help from Meryl Horn, Rose Rimler and Lexi Krupp. Our senior producer is Kaitlyn Sawrey. We’re edited by Caitlin Kenney and Blythe Terrell. Fact checking by Diane Kelly. Mix and sound design by Peter Leonard. Music by Peter Leonard, Emma Munger and Bobby Lord. Recording assistance from Joel Cox, Andrea Rangecroft, Natalie Jones, and Mark Totti. A huge thanks to all the scientists we got in touch with for this episode, including Professor Virginia Berridge, Professor James Blumenthal, Professor Kirk Erickson, Dr Tara Walker, Dr Shannon Halloway, Professor Steven Petruzzello, Dr Kristine Beaulieu, Dr Aric Sudicky and many others! A special thanks to the Emmanuel Dzotsi, Zukerman family, and Joseph Lavelle Wilson.
I’m Wendy Zukerman, fact you next week.
[1]CDC: Among adolescents aged 16-19 who tried to lose weight, the most commonly reported way was exercising (83.5%).
[2] During the 1970s the American public seems to have “discovered” exercise. A 1977 Gallup poll showed that the number of adults who exercise has almost doubled since 1960 to close to 50% of our population … It has been estimated that the number of joggers now stands at 10 to 23 million (2), serious swimmers at 15 million (89), regular cyclists at 15 million (89), and tennis players at 29 million (56)
[4] https://www.ncbi.nlm.nih.gov/pubmed/17557987 Eligible participants were 40 to 75 years old
[5] :Technically, all the subjects were sedentary, and many were overweight, but the BMI range reported in the paper includes some subjects at healthy weights (BMI < 25). Average of 28 to 30 BMI on Table 1 https://onlinelibrary.wiley.com/doi/full/10.1038/oby.2007.178 https://www.nhlbi.nih.gov/health/educational/lose_wt/BMI/bmicalc.htm
[6] Three days per week, participants exercised on treadmills, stationary bikes, elliptical machines, and rowers with an exercise specialist present at one of four facilities (one located at the Fred Hutchinson Cancer Research Center Prevention Center, A. McTiernan, Director, and three private health clubs).
[7] Several methods were used to measure and monitor adherence, including facility class attendance (with data on type, length, and maximal heart rate entered on facility logs, verified by the exercise specialist, and data entered), home exercise logs (with data on type, length, and maximal heart rate entered, submitted weekly, reviewed by the exercise specialist, and data entered), quarterly MNLTPA interviews, quarterly use of pedometers for 1 week with logging of steps, and Vo2max treadmill tests at baseline and 12 months.
[8] Exercisers lost weight (women, −1.4 vs. +0.7 kg in controls, p = 0.008; men, −1.8 vs. −0.1 kg in controls, p = 0.03),
[9] Increases in physical activity of the amount common for most individuals, such as 3 days/week of 1 h of aerobic activity, will not lead to weight loss, nor will it help prevent weight gain, for the majority of the population.
[10] A study from 2015 found that exercising alone doesn’t help you shed pounds, though it can help maintain weight. Also see: https://www.aomrc.org.uk/wp-content/uploads/2016/05/Exercise_the_Miracle_Cure_0215.pdf
[11] A series of studies conducted over the last 10 years provides a body of data which suggests that reduction in physical activity has a minor or non-existent role in the etiology of the contemporary obesity epidemic. See this 2009 study, another study from 2009, this meta-analysis from 2011, and this study from 2012.
[12] HUNT study: Men maintaining physical activity above the recommendations for 33 years increased 5.6 kg, while inactive men increased 9.1 kg. For women, corresponding numbers were 3.8 kg in those above recommended physical activity levels, and 9.5 kg in inactive.
[14] The association between prospectively assessed physical activity and either body weight or WC was examined in 4944 participants of the Doetinchem Study (men and women aged between 26 and 66 y at baseline).
[15] On average, all participants experienced weight and waist circumference gains independent of their changes in physical activity levels
[16] https://nutritionandmetabolism.biomedcentral.com/articles/10.1186/1743-7075-7-17 for obese women who did resistence training for 10 weeks, “The Ex group ... had a significant increase in LBM (1.6 ± 1.8 kg, p = 0.045). [3.5 pounds]” Variation in Lean Body Mass consist of changes in body water and muscle mass
[17] https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3761774 college athletes: high protein diet for 8 weeks (working out 4x per week), both types of protein caused increase in 1.5/1.4kg of lean mass
[18] https://journals.humankinetics.com/view/journals/ijsnem/27/5/article-p448.xml 9-week RT program for 31 resistance-trained men: LBM increased significantly with time in FP(100) (from 58.9 ± 6.8kg to 60.4 ± 7Kg), FP(50) (from 60.2 ± 5.5kg to 61.9 ± 6Kg), and FP(20) (from 62 ± 5.4kg to 63.4 ± 5Kg) [= 1.5kg, 1.7kg, 1.4 kg]
[19] “A long-standing consistent observation is that regular exercise by itself is prescribed in small to moderate amounts resulting in modest weight loss or in some cases weight gain” https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3771367/
[20] And we’ve known this for a while… like since 2004: “Current debates rage around the amount of Physical Activity (PA) which might be required to [i] prevent weight gain in populations, and [ill induce and maintain weight loss in populations already obese or overweight…. The International Association for the Study of Obesity (IASO) consensus group reported on the deliberations of a meeting held in 2002 … However, "for the prevention of weight regain in formerly obese individuals, at least 60-90 minutes of moderate intensity PA or lesser amounts of vigorous PA are required". “
[21] E.g. From their meta-analysis, Schubert et al. [21] found that absolute energy intake after acute exercise was greater in active individuals than in less active individuals, whereas Donnelly et al. [20] concluded from their systematic review that increased physical activity or exercise, regardless of physical activity level, had no consistent effect on acute or long-term energy intake. And look at Figure 2 - it’s all over the shop!
[22]Given that an hour of vigorous activity is required to expend roughly 500 calories, leisure-time activity cannot be playing any noticeable role in the energy budget of the US population.; estimate of calories expended by exercise: https://www.health.harvard.edu/diet-and-weight-loss/calories-burned-in-30-minutes-of-leisure-and-routine-activities
[23] “ The Liking and Wanting procedure was also used in the 12-week exercise intervention to assess changes in taste and nutrient preferences under more chronic energy balance conditions. Those who experienced an immediate post-exercise increase in liking for food in general, and an increased wanting for high-fat sweet foods also experienced less weight loss” https://www.ncbi.nlm.nih.gov/pubmed/23470300
[24] Twelve of 13 individuals from which changed body composition and DLW-assessed energy expenditures were obtained in the study of Westerterp et al. increased intake during the respective intervention. Additionally, Woo et al. found that five lean women increased intake to match their increased energy expenditures during the intervention, but did not observe the same result for the six obese women.” https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3771367/
[25] https://www.sciencedirect.com/science/article/abs/pii/S019566631630424X “Greater EI, primarily driven by chocolate chip cookie consumption (p = 0.015), was observed in participants receiving 265 kcal EE information. “
[26] This paper found that people who exercised for controlled reasons e.g. guilt were more likely to have this licensed belief of eating an unhealthy snack https://www.sciencedirect.com/science/article/abs/pii/S1469029217301590?via%3Dihub
[27] people who lose little or no weight in response to adding structured exercise must be compensating for the increased EE of exercise by reducing their non-exercise physical activity and/or increasing their EI (energy input)
[28] However, other studies show that exercise does not seem to immediately affect hunger https://eprints.qut.edu.au/80100/1/80100.pdf
[29] Some (not all) people compensate for the lost calories: “First of all, it is clear that any compensatory increase in EI, which could offset the exercise induced EE, is not uniform. Compensation varies markedly from person to person. One reason for this is the observed effects of exercise on different components of appetite control.”
[30] See Table 1 combined sample: https://www.researchgate.net/profile/Jasper_Smits/publication/265019301_The_Development_of_a_Novel_Measure_to_Assess_Motives_for_Compensatory_Eating_in_Response_to_Exercise_The_CEMQ/links/56aa5dc808aed5a0135895f0/The-Development-of-a-Novel-Measure-to-Assess-Motives-for-Compensatory-Eating-in-Response-to-Exercise-The-CEMQ.pdf
[31] However, the effect of exercise on fasting hunger is quite variable. Therefore it can be deduced that the range of the effects of exercise on overall EI is a function of the individual change in basal hunger together with the adjustment in postprandial satiety
[32] A systematic literature search yielded 14 eligible studies for review. Six studies tested the relationship between affective states and subsequent physical activity; findings from these studies suggest that positive affective states were positively associated with physical activity over the next few hours while negative affective states had no significant association. Twelve studies tested affective states after physical activity and yielded consistent evidence for physical activity predicting higher positive affect over the next few hours
[33] Only half the subjects released true endorphin upon exercise: “only minor amounts of authentic b-endorphin(1-31) had been released under our experimental conditions, but major amounts of one or several b-endorphin derivatives containing the b-endorphin (17-24) fragment”
https://www.sciencedirect.com/science/article/abs/pii/S0306453000000093?via%3Dihub: and their presence was fleeting: “In most participants, there was a sharp decrease of b-endorphin IRM from the peak values measured immediately after to the levels measured 15 min after exercise.”
[34] PET study with labeled opioid ligand: The level of euphoria was significantly increased after running and was inversely correlated with opioid binding in prefrontal/orbitofrontal cortices, the anterior cingulate cortex, bilateral insula, parainsular cortex, and temporoparietal regions
[35] These findings provide the first evidence that exercise activates the endocannabinoid system and are suggestive of a new neurohumoral mechanism for exercise analgesia.; intense exercise increased circulating endocannabinoids in humans: https://www.sciencedirect.com/science/article/abs/pii/S0306453011002873
[36] We excluded studies that measured outcomes immediately before and after a single exercise session, and trials which provided less than a week of exercise.
[37] We excluded trials that randomised people both with and without depression, even if results from the subgroups of participants with depression were reported separately, as we had done in previous versions of the review
[38] When we included only the six trials (464 participants) with adequate allocation concealment, intention‐to‐treat analysis and blinded outcome assessment, the pooled SMD for this outcome was not statistically significant (‐0.18, 95% CI ‐0.47 to 0.11).
[39]When only high‐quality trials were included, the effect size was small and not statistically significant. Of the eight trials (377 participants) that provided long‐term follow‐up data, there was only a small effect in favour of exercise (SMD ‐0.33, 95% CI ‐0.63 to ‐0.03) at the end of long‐term follow‐up, This suggests that any benefits of exercise at the end of treatment may be lost over time. Thus, exercise may need to be continued in the longer term to maintain any early benefits. Our summary of findings tables indicate that the quality of evidence is low
[40] 2011: Exercise interventions may have a small, short-term beneficial effect in relieving symptoms of patients experiencing depression. There was no evidence that this small effect for interventions continued beyond 10 weeks; there was no long-term effect beyond the end of the intervention.
[41] One of the main reasons for this striking lack of progress is covert heterogeneity of depression: the current diagnostic criteria and common research practices lump individuals suffering from diverse psychiatric symptoms into one undifferentiated category
[42] Parker (2005) concluded that depression fails to meet orthodox criteria for validity such as a clear clinical presentation, precise diagnostic boundaries, and treatment specificity.
[43] Spoke to source who mentioned people benefit a lot; also see Blumenthal et al 1999: https://jamanetwork.com/journals/jamainternalmedicine/fullarticle/485159
[44] UPDATE 10/31/19: An earlier version of this episode said that exercise isn’t a reliable treatment for depression. Some scientists reached out to us about clinical trials we missed that do show exercise can help with depression, which show that the research in this space is stronger than we made it sound. We’ve updated the episode accordingly.
[45] https://www.researchgate.net/profile/Mats_Hallgren/publication/278788898_Physical_exercise_and_internet-based_cognitive-behavioural_therapy_in_the_treatment_of_depression_Randomised_controlled_trial/links/5bd452ca92851c6b27926f8f/Physical-exercise-and-internet-based-cognitive-behavioural-therapy-in-the-treatment-of-depression-Randomised-controlled-trial.pdf
[47] Participants wore a pulse-watch (Polar RCX3, Polar Electro Sweden) when designing their program. The two individual sessions took place during the initial two weeks of the study period. Thereafter followed an 8-week period with two weekly sessions during which 5–8 participants trained at the same time, guided by the same physical therapist https://www.sciencedirect.com/science/article/abs/pii/S0165032714004170?via%3Dihub
[48] Adherence was monitored through weekly face-to-face meetings with a qualified personal trainer and patients who failed to attend this meeting were contacted by the trainer with a telephone call and encouraged to continue the exercise intervention. Reminder text messages were sent to patients who could not initially be contacted by telephone. https://www.researchgate.net/profile/Mats_Hallgren/publication/278788898_Physical_exercise_and_internet-based_cognitive-behavioural_therapy_in_the_treatment_of_depression_Randomised_controlled_trial/links/5bd452ca92851c6b27926f8f/Physical-exercise-and-internet-based-cognitive-behavioural-therapy-in-the-treatment-of-depression-Randomised-controlled-trial.pdf
[49] Spoke to J Blumenthal who mentioned people benefit a lot; also see Blumenthal et al 1999: https://jamanetwork.com/journals/jamainternalmedicine/fullarticle/485159
[50] https://jamanetwork.com/journals/jama/fullarticle/201494 (PubMed: https://www.ncbi.nlm.nih.gov/pubmed/16160134); CDC 2017 data, Fig 4: https://www.cdc.gov/nchs/products/databriefs/db328.htm
[51] " The findings of this update are consistent with the previous (2011) version of this Cochrane review and show important benefits of exercise-based cardiac rehabilitation that include a reduction in the risk of death due to a cardiovascular cause and hospital admission and improvements in health-related quality of life, compared with not undertaking exercise. " https://www.cochrane.org/CD001800/VASC_exercise-based-rehabilitation-coronary-heart-disease
[52] Data from the MRFIT showed that men at high risk for CHD who self-selected moderate amounts of predominantly light and moderate non-work physical activity had lower rates of CHD mortality, sudden death, and overall mortality than more sedentary men
[53] Compared with control exercise training reduced the rate of overall (15 trials, 1328 participants, RR: 0.75; 95% CI : 0.62-0.92, fixed-effect analysis) and heart failure specific hospitalizations (12 trials, 1036 participants, RR: 0.61; 95% CI : 0.46-0.80, fixed-effect analysis)
[54] Morris discovered that bus conductors, whose task it was to walk up and down London’s double-decker buses collecting fares, had only 70% of the incidence of total manifestations of coronary heart disease found in the more sedentary bus drivers. More significantly, conductors had only 53% of the incidence of myocardial infarction (MI) and 46% of the overall CHD mortality of the drivers.
[56] Bus conductors had half the rate of coronary thrombosis of bus drivers, postmen had half the heart attack rate of office clerks https://radar.brookes.ac.uk/radar/file/2d190b9a-e481-43e6-9956-5b39be502f63/1/InteractiveTranscript.html
[57] Discussed here: cohort studies from 1947-1972 http://www.epi.umn.edu/cvdepi/study-synopsis/london-transport-workers-study/
[58] An association has been demonstrated between physical activity/inactivity of work and one form of coronary heart disease, ischaemic myocardial fibrosis. “About 5,000 reports were received, made up in round numbers thus: 1,200 deaths from coronary heart disease, etc. (Group A); 1,000 deaths from conditions with a specially high prevalence of coronary artery disease-for example, deaths caused by hypertension and its complications, deaths diabetics, deaths from arterial disease in other sites (Group B); and, the remainder, 2,800 deaths from miscellaneous conditions, their main causes having no particular association with coronary artery disease-for example, injuries, infections, cancer”
[59] The medical and scientific community initially met these results with skepticism, but by the 1970s it became an accepted notion that men who exercised regularly had a lower risk of death from heart disease and stroke, independent of obesity, diet, and blood pressure.
[60] A large body of epidemiological evidence demonstrates that high levels of physical activity and physical
fitness are associated with a lower risk of developing CHD. RCTs show that regular physical activity can
favourably modify CHD risk factors, including (but not limited to) dyslipidaemia, hypertension and obesity.
RCTs also show that physical activity improves survival in CHD patients
[61] Once symptomatic CAD has developed, regular exercise training is a potent strategy to increase the threshold of angina‐free activity levels in stable disease conditions. Furthermore, exercise training seems to attenuate disease progression and improve event‐free survival in the secondary prevention of CAD
[62]E.g. Secretion of the adrenal hormones cortisol and adrenaline is increased during exercise… Cortisol is known to have potent anti-inflammatory effects50, and catecholamines downregulate the lipopolysaccharide (LPS)-induced production of cytokines (including TNF and IL-1β) by immune cells. (But see Figure 2 for more)
[63] Regular exercise reduces the risk of chronic metabolic and cardiorespiratory diseases (TABLE 1), in part because exercise exerts anti-inflammatory effects
[64] Following acute exercise such as running at 75% of VO2max, the basal plasma IL‐6 may increase fivefold after 30 min 30, but the concentration may increase up to 100‐fold after a marathon…In relation to acute exercise, IL‐6 induces a subsequent increase in the production of IL‐1 receptor antagonist (IL‐1ra) and IL‐10 by blood mononuclear cells, thus stimulating the occurrence of anti‐inflammatory cytokines… studies in humans suggest that moderate acute elevations in IL‐6 and IL‐10, as provoked by exercise, exert anti‐inflammatory effects
[65] Exercise is now considered to be not only of prophylactic value, but also an effective
therapy for many conditions and diseases.
[66] https://as.nyu.edu/content/nyu-as/as/faculty/wendy-suzuki.html
[67] “Basically, the responses depend on the level of the subjects and the stimuli but, as it is an acute response, I would expect some positive effects during the first 30 min after exercise, with greater responses in trained individuals and with higher exercise intensities.” - source
[68] E.g. In this study the test was done 10 minutes after exercise: Within the 10 min following the cessation of the spinning exercise bout, the participant started the true experimental trials of the ANT.
[69] When studies that tested cognition following exercise were combined, the timing of the test administration following the exercise did significantly influence the effect sizes observed with
tests completed within 0–10 min of exercise completion resulting in significant negative effects, the largest positive effects observed following 11–20 min of delay, and smaller positive effects evident following 20 min of delay.
[70] Review paper: The majority of studies found a positive association between exercise, fitness, and attention, while a few studies found no association. “Aerobic exercise training interventions generally resulted in positive changes, while some resistance training studies detected no evidence of an effect.”
[71] Consistent with past findings, analyses indicated that the overall effect was positive and small (g = 0.097 n = 1034). Positive and small effects were also found in all three acute exercise paradigms: during exercise (g = 0.101; 95% confidence interval [CI]; 0.041–0.160), immediately following exercise (g =0.108; 95% CI; 0.069–0.147), and after a delay (g = 0.103; 95% CI; 0.035–0.170)
[73] Commentary on the research: https://n.neurology.org/content/90/15/675
[74] systematic subsample (born on the sixth day of uneven months, e.g., January, March, etc) were admitted to an exercise test, and 191 took part … Cardiovascular fitness was tested at baseline in 1968 by a stepwise-increased ergometer cycling test until exhaustion that was supervised by a physician.
[75] A population-based sample of 1,462 women 38 to 60 years of age was examined in 1968. Of these, a systematic subsample comprising 191 women completed a stepwise-increased maximal ergometer cycling test to evaluate cardiovascular fitness.
[76] Follow-ups for dementia diagnoses were performed in 1974 to 1975 (n = 174, 8 had died, 9 refused), 1980 to 1981 (n = 147, 20 had died, 24 refused), 1992 to 1993 (n = 99, 57 had died, 35 refused), 2000 to 2001 (n = 68, 92 had died, 31 refused), 2005 to 2006 (n = 46, 118 had died, 27 refused), and 2009 to 2010 (n = 13, 151 had died, 27 refused). Cases of dementia were also identified via the Swedish Hospital Discharge Register until December 2012.
[77] High fitness delayed age at dementia onset by 9.5 years and time to dementia onset by 5 years compared to medium fitness.
[78] We found that high cardiovascular fitness in midlife was associated with decreased risk of dementia in a population of women followed up for up to 44 years. High compared to medium fitness decreased the risk of dementia by 88%.
[79] Guidelines: Strong evidence demonstrates that greater amounts of physical activity are associated with a reduced risk of developing cognitive impairment, including Alzheimer’s disease. PAGAC Grade: Strong… For example, a meta-analysis of 15 prospective studies of 1 to 12 years in duration with more than 33,000 participants found that greater amounts of physical activity were associated with a 38 percent reduced risk of cognitive decline.20 Another meta-analysis of 10 prospective studies with more than 20,000 participants reported that greater amounts of physical activity were associated with a 40 percent reduced risk of developing AD
[81] Exercise has been shown to have fewer side effects and better adherence compared to medications; Mild to moderate exercise over a 1-yr period appears to prevent hippocampal volume atrophy.
[82] One meta-analysis (Williams et al., 2010) shows that the hazard ratio for developing Alzheimer’s disease is 0.718 (0.525–0.982), which corresponds to physical activity, especially of high intensity, being associated with an approximately 28% reduced risk.
[83] Review of 11 studies: Physical exercise, aerobic exercise in particular, benefits global cognition in MCI patients. The evidence of physical exercise on domain-specific cognitive function and psychological outcomes remains unclear, more trials with rigorous study design are necessary to provide the evidence.
[84] Physical exercise improved cognitive function in the over 50s, regardless of the cognitive status of participant
[85] A 2010 meta-analysis (Aarsland et al., 2010) concludes that physical activity prevents vascular dementia. The analysis, which includes 24 studies, finds a significant association between physical activity and a reduced risk of 0.62 (95% CI: 0.42–0.92) for developing vascular dementia. Other studies show that regular physical activity prevents Alzheimer’s disease.
[86] Not all of these studies - there are some small RCTs e.g. year long - found improvements for elderly adults with mild cognitive impairment (not dementia) https://www.ncbi.nlm.nih.gov/pubmed/23113898
[87] Although many studies show a strong correlation between exercise and a reduced risk of dementia, there is as yet little evidence that exercise is effective as an interventional tool for delaying cognitive decline. “However, despite evidence accumulated over decades from observational studies showing the significant benefit of physical activity for reducing the risk of cognitive decline and dementia (Blondell et al., 2014; Brown et al., 2013), supportive data from intervention studies have been sparse, with meta-analyses reporting both no benefit (Young et al., 2015) and benefit (Northey et al., 2017; Zheng et al., 2016).; with the exception of the LIFE study, all RCTs included in the AHRQ systematic review were of short duration (1 year or less). ….One year or less is likely much too short a time in which to assess intervention effects on the risk of Alzheimer’s disease and related dementias.
[89] Changes in hippocampal structure may be mediated by trophic factors, such as insulin-like growth factor 1 (IGF-1) and brain-derived neurotrophic factor (BDNF) (Ferris et al., 2007, Vaynman et al., 2004)
[90] 4 days of running are sufficient to significantly increase the number of proliferating neural precursor cell (NPCs) in the hippocampal dentate gyrus (DG)
[91] Mice were injected with bromodeoxyuridine to label dividing cells and trained in the Morris water maze. LTP was studied in the dentate gyrus and area CA1 in hippocampal slices from these mice. Running improved water maze performance, increased bromodeoxyuridine-positive cell numbers, and selectively enhanced dentate gyrus LTP.
[92] The impact of aerobic exercise on hippocampal size and function has been extensively studied in rodents (Van Praag et al., 2005). These animal studies have shown that voluntary exercise is associated with hippocampal neurogenesis (Van Praag, 2008) and prevents age-related decline in cell-proliferation in this brain structure.
[93] it is considered central to our understanding of the brain basis of episodic memory, the hippocampus (HPC) ... much as it is considered the hub of regions dealing with episodic memory.; The HPC sits at the top of a hierarchy of largely cortical systems (the ventral and dorsal streams) in which later stages integrate information from previous ones, building more complex representations in the process and influencing the operation of earlier stages through back projections (Nadel & Peterson 2013)
[94] A very influential case was that of H.M. [4], who, following bilateral hippocampal surgery to relieve intractable epilepsy, became densely amnesic and unable to form ongoing memories. He could, however, perform normally on short-term memory tasks such as hearing and repeating back a telephone number. … Other patients, with damage to the left temporo-parietal cortex rather than the hippocampus, were reported to have exactly the opposite pattern of deficits, suggesting preserved long-term but impaired short-term memory.
[95] Greater PA [Physical Activity] predicted greater volumes of frontal, occipital, entorhinal, and hippocampal regions 9 years later. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3039208/?_escaped_fragment_=po=56.6667
[96] Review of studies assessing hippocampal volume via MRI: A random-effects meta-analysis showed no significant effect of aerobic exercise on total hippocampal volume across the 737 participants. However, aerobic exercise had significant positive effects on left hippocampal volume in comparison to control conditions. https://www.sciencedirect.com/science/article/pii/S1053811917309138
[97] People with dementia have low levels of BDNF (Kim et al., 2011). A randomized controlled trial with 120 older adults showed that aerobic exercise training increases the size of the anterior hippocampus, leading to improvements in spatial memory. Exercise training increased hippocampal volume by 2%, effectively reversing age-related loss in volume.
[98] As predicted, higher cardiorespiratory fitness levels were associated with larger hippocampal volumes, and larger hippocampal volumes were, in turn, associated with better memory performance on a spatial memory task independent of age and education levels.
[99] https://www.sciencedirect.com/science/article/pii/S1053811917309138 "The neurochemical mechanisms through which exercise promotes retention of hippocampal volume in aging humans has not been fully established. However, a comprehensive narrative review examining the neurological effects of exercise across the lifespan (Voss et al., 2011) found evidence from animal models supporting the theory that aerobic exercise acts by preventing the usual decrease in neurogenesis associated with aging, thus resulting in greater retention of neural matter – particularly in the hippocampus. "
[100] In the Guidelines, compared to 2008. The 2018 Scientific Report demonstrates, for the first time, the positive effects of physical activity on biomarkers of brain health obtained from neuroimaging techniques (e.g., brain volume).
[101] https://www.cdc.gov/nchs/fastats/leading-causes-of-death.htm
[103] There is growing epidemiological evidence that a physically active lifestyle protects against the development of colon cancer, breast cancer, endometrial cancer, and prostate cancer (Thune and Furberg, 2001; Samad et al., 2005; Harriss et al., 2009; Wolin et al., 2009; Eliassen et al., 2010; Schmitz et al., 2010; George et al., 2011; Kenfield et al., 2011). In recent years, a number of observation studies have shown that people who are physically active after being diagnosed with breast cancer or colon cancer have a statistically higher chance of survival compared to those who are physically inactive. According to these studies people who are physically active… almost double their chance of survival (Holmes et al., 2005; Meyerhardt et al., 2006a, b, 2009; Peel et al., 2009; Ibrahim and Al-Homaidh, 2011).
[104] Moore and colleagues recently pooled data from 12 prospective cohorts with self-reported physical activity for association with incidence of 26 types of cancer, and could demonstrate that leisure-time physical activity is significantly associated with a lower risk of cancer, e.g., cancers of the oesophagus, liver, lung, kidney, colon, breast, and as well as leukemia and myeloma [2]. Strikingly, two cancers showed physical activity associated with higher risk of cancer, melanoma, and prostate cancer. For melanoma, this could supposedly be due to sun exposure during exercise. For advanced prostate cancer, there was no relationship between physical activity and cancer, suggesting that men that exercise, are more prone to be examined and diagnosed—in some cases with indolent prostate cancer (see Moore et al 2016 https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5812009/ for details)
[105] Lower the risk of cancer “Exercise is one of several lifestyle factors known to lower the risk of developing cancer.”
[106] A survey of more than 300 people found that only 3% were aware that exercise reduced cancer)
[107] See Figure 1: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5812009/
[108] https://www.wcrf.org/sites/default/files/Physical-activity.pdf: strong evidence for exercise reducing risk of colon, endometrial, breast cancers
[109] Strong evidence demonstrates that greater amounts of physical activity are associated with reduced risk of developing bladder cancer. PAGAC Grade: Strong.
https://health.gov/paguidelines/second-edition/report/pdf/10_F-4_Cancer_Prevention.pdf
[110] Strong evidence demonstrates that greater amounts of recreational, occupational, or total physical activity are associated with a lower risk of developing adenocarcinoma of the esophagus. PAGAC Grade: Strong.
[111] BUT WCRF said limited - suggestive evidence: for esophageal cancer: https://www.wcrf.org/sites/default/files/Physical-activity.pdf
[112] WCRF also said strong evidence for risk reduction in colon, breast (postmenopausal), and endometrial cancers: https://www.wcrf.org/sites/default/files/Physical-activity.pdf
[113] Strong evidence demonstrates that greater amounts of recreational, occupational, or total physical
activity are associated with a lower risk of developing colon cancer. PAGAC Grade: Strong.
[114] Strong evidence/Probable for breast cancer: https://www.wcrf.org/sites/default/files/Physical-activity.pdf
[115] Strong evidence demonstrates that greater amounts of physical activity are associated with a lower risk of breast cancer. PAGAC Grade: Strong
[116] WCRF said strong/probable evidence that physical activity decreases risk for endometrial cancer: https://www.wcrf.org/sites/default/files/Physical-activity.pdf
[117] Strong evidence demonstrates that greater amounts of physical activity are associated with a lower risk of endometrial cancer. PAGAC Grade: Strong.
[119] Kenfield et al. 2011: she started by looking for men who were (1) diagnosed after 1990, (2) didn't have markers for advanced prostate cancer (low stage, didn't die by 1994), and (3) had provided activity data before and after diagnosis. Afterwards, her model for mortality from PC took treatment type into account (among other things, like age) [https://www.ncbi.nlm.nih.gov/pubmed/21205749
[120] We evaluated physical activity in relation to overall and PCa mortality among 2,705 men in the Health Professionals Follow-Up Study diagnosed with nonmetastatic PCa observed from 1990 to 2008
[121] When evaluating walking separately, a significant benefit was observed at levels of ≥ 7 hours of walking per week (HR, 0.64; 95% CI, 0.47 to 0.86) versus < 20 minutes per week (Ptrend = .003).
[122] We don't know whether exercise will affect all cancers this way: From recent meta-analysis: "Insufficient data exist to determine if the degree of apparent protection varies according to cancer type, stage, and/or treatment regimen." https://academic.oup.com/epirev/article/39/1/71/3760392
[123] Engaging in exercise following the diagnosis of cancer was observed to have a protective effect against cancer-specific mortality, cancer recurrence, and all-cause mortality …. Although the majority of these studies are observational and therefore cannot infer causation, the apparent protective effect of exercise was observed in multivariable-adjusted analyses that account for a range of clinically relevant covariates associated with cancer progression (e.g., cancer stage, treatments, smoking status, body mass index, comorbidities, and so on).
[124] “Exercise promotes significant improvements in clinical, functional, and in some populations, survival outcomes and can be recommended regardless of the type of cancer.”
[125] “ this review confirms that cancer patients involved in greater levels of exercise have a lower relative risk of cancer mortality and a lower relative risk of cancer recurrence, and they experience fewer and/or less severe treatment-related adverse effects.” https://academic.oup.com/epirev/article/39/1/71/3760392
[126] Engaging in exercise following the diagnosis of cancer was observed to have a protective effect against cancer-specific mortality, cancer recurrence, and all-cause mortality...Although the majority of these studies are observational and therefore cannot infer causation, the apparent protective effect of exercise was observed in multivariable-adjusted analyses that account for a range of clinically relevant covariates associated with cancer progression (e.g., cancer stage, treatments, smoking status, body mass index, comorbidities, and so on).
[127] A considerable body of literature now exists that provides convincing evidence of the beneficial impact of exercise on disease and patient outcomes.
[128] A range of potential factors and mechanisms may contribute to the relationship observed between exercise behavior and cancer progression. Exercise may reduce the risk of cancer mortality and recurrence by enhancing the ability of patients to physically tolerate greater dosages of cancer treatment (119, 120). Similarly, improved fitness has been associated with enhanced surgical outcomes including less complications and morbidity...
[129] Other ideas: Exercise has been shown to increase the levels of IGFBP3 and lower IGF-1, and in a large prospective cohort study of 41 528 participants, this was associated with a 48% reduction of cancer-specific deaths; exercise is also associated with upregulation of DNA repair genes.
[130] Physical activity may lower cancer risk by systemic mechanisms (such as reduced body fat and insulin levels, and enhanced immune function) and site-specific mechanisms (namely, reduced levels of sex steroid hormones for breast cancer, and decreased bowel transit time for colon cancer)
[131] We see it in mice models too. Exercise had a signifcant impact on tumor size in the transplanted lewis lung cancer and B16 melanoma models—the latter studied both as subcutaneous (s.c.) tumors, as well as lung metastases
[132] In mice models: Tumors from exercise animals had a much denser infltration of immune cells; T cells, B cells, dendritic cells, and NK cells. When researchers knocked out this effect of NK Cells - no more anti tumour response. We went back to using B16 melanoma in wild type C57BL/6 mice, and used anti-asialo monoclonal antibody to clear NK cells from the animals. Strikingly, this completely abolished the efect of exercise, demonstrating that at least in the used transplanted tumor model, NK cells were necessary and sufficient for the effect [5]. NK cells are known to be capable of killing cancer cells [6], but a link between NK cells and the exercise associated anti-tumor response had not previously been scrutinized.
[135]First, we evaluated the effect of wheel running before and/or during tumor challenge in a subcutaneous B16F10 melanoma model in female mice
[136] We recently took advantage of several murine tumor models to study the impact of exercise on cancer, and could demonstrate that voluntary exercise (wheel running) leads to a signifcant reduction in tumor size or incidence across the applied models; https://www.ncbi.nlm.nih.gov/pubmed/26895752
[137] Figure 3 F https://www.cell.com/cell-metabolism/fulltext/S1550-4131(16)30003-1?_returnURL=https%3A%2F%2Flinkinghub.elsevier.com%2Fretrieve%2Fpii%2FS1550413116300031%3Fshowall%3Dtrue
[138] natural killer cells. Exercise increases #s of NK cells in the blood plasma; https://www.immunology.org/public-information/bitesized-immunology/cells/natural-killer-cells: NK cells ‘read’ the surface of cells in the body and kill any that lack the correct ‘self’ signals. This mechanism can identify virus-infected cells and some cancer cells. Also bacteria: https://link.springer.com/chapter/10.1007/978-3-642-02309-5_7
[139] It’s possible that NK cells may home in onto cancers - by binding to their receptors
[140] https://www.immunology.org/public-information/bitesized-immunology/cells/natural-killer-cells: Once the decision is made to kill, the NK cell releases cytotoxic granules containing perforin and granzymes, which leads to lysis of the target cell.
[144] Living longer https://www.ncbi.nlm.nih.gov/pubmed/23139642
[145] There is strong evidence suggesting that exercise from low to high intensity of various modes is effective in improving disease-related characteristics and functional ability in RA patients.