Can Endurance Exercise Promote Cancer?

I got into a bit of trouble in the comments a few weeks back when I joked that Grete Waitz may have died from marathoning. Steve replied:

Paul, you said “… marathoning (from which Grete Waitz just died at 57)”

Gee. The news said cancer. How confident are you that she died “from” running marathons?

Of course, not confident at all. Maybe if she’d been a sprinter she would have died at 54. Maybe if Lance Armstrong had been a couch potato he would still have had testicular cancer metastasized to his brain and lung at age 25.

A few days ago I got an email. Two highly fit endurance athletes, both of whom have always tended to their health and been careful to eat “healthy” (i.e. vegetable and whole grain rich, meat and fat poor) diets, have contracted cancers in the prime of life and been given less than a year to live. My correspondent asked, “Why?”

Let’s look into this. Is it possible that endurance exercise, especially if combined with a high-carb diet, may promote cancer?

Oxidative Damage to DNA and Cancer

Human DNA is constantly being damaged and repaired. It’s been estimated that over the course of a cell cycle – that is, from the time a cell is formed to the time it divides into two daughter cells – a human cell develops 5,000 single-stranded DNA breaks due to oxidative damage from reactive oxygen species (ROS). The vast majority are repaired by the body’s DNA repair machinery. [1]

However, in typical human cells 0.1% or 5 are not successfully repaired; instead a corresponding break is created in the complementary DNA strand, resulting in a double-strand break. In people with Bloom syndrome, an inherited condition which creates a strong predisposition to cancer, fully 1% or 50 are not successfully repaired. [1]

The double-strand break leads to a re-arrangement or “translocation” of parts of the chromosome. Usually, this does not break the coding region for a protein, but it does break non-coding regions resulting in changes to gene expression.

These sorts of genetic changes are observed both in cancer and in aging. [1] In short, oxidative damage to DNA is considered a risk factor for cancer development.

Oxidative Damage to DNA Has Been Specifically Linked to Endurance Exercise

Diets and activities that increase oxidative stress – for instance, diets deficient in antioxidant minerals – can therefore increase cancer risk. And diets and activities that minimize oxidative stress can minimize cancer risk and facilitate recovery.

Endurance exercise generates oxidative stress. Marathon running “caused a large increase in the tissue content of oxidized glutathione (189%) at the expense of reduced glutathione (-18%).” [2]

Moreover, endurance exercise damages DNA:

Both a systemic inflammatory response as well as DNA damage has been observed following exhaustive endurance exercise….

Extremely demanding endurance exercise has been shown to induce both a systemic inflammatory response [15, 42, 53, 71] as well as DNA damage [21, 36, 58, 62, 80]….

Exercise-induced DNA damage in peripheral blood cells appear to be mainly a consequence of an increased production of reactive oxygen and nitrogen species (RONS) during and after vigorous aerobic exercise [58]. Besides oxidative stress, other factors such as metabolic, hormonal and thermal stress in addition to the ultra-structural damage of muscle tissue are characteristic responses to prolonged strenuous exercise, that can lead to the release of cytokines, acute phase proteins and to the activation or inhibition of certain lines of the cellular immune system [15, 29]. [3]

There seems to be a big difference between moderate exercise and exercise to exhaustion. Moderate exercise actually protects DNA by upregulating DNA repair:

Sato et al. showed that acute mild exercise as well as chronic moderate training does not result in DNA damage, but rather leads to an elevation in the sanitization system of DNA damage [66]. [3]

However, endurance exercise leads to increased DNA damage:

Increased levels of DNA strand breaks were observed after exhaustive treadmill running in subjects of different training status [22, 45]….

In conclusion, there is growing evidence that strenuous exercise can lead to DNA damage that with few exceptions [36] is predominantly observed not before 24 h after the resolution of exercise [21, 44, 45, 80]. [3]

In addition, strenuous endurance exercise induces hormonal and other changes which might promote cancer. An Ironman triathlon has significant effects on hormones and inflammatory markers, some of which persist for more than 19 days post-race:

Briefly, as described in details elsewhere [42], there were significant (P<0.001) increases in total leukocyte counts, MPO, PMN elastase, cortisol, CK activity, myoglobin, IL-6, IL-10 and hs-CRP, whereas testosterone significantly (P<0.001) decreased compared to pre-race. Except for cortisol, which decreased below pre-race values (P<0.001), these alterations persisted 1 d post-race (P<0.001, P<0.01 for IL-10). Five days post-race CK activity, myoglobin, IL-6 and hs-CRP had decreased, but were still significantly (P<0.001) elevated. Nineteen days post-race most parameters had returned to pre-race values, with the exception of MPO and PMN elastase, which had both significantly (P<0.001) decreased below pre-race concentrations, and myoglobin and hs-CRP, which were slightly, but significantly higher than pre-race [42]. [3]

In the opinion of the authors of this review, the biggest problem is production of reactive oxygen and nitrogen species (RONS) by damaged immune cells:

The most conclusive picture that emerges from the available data is that oxidative stress seems to be the main link between exercise-induced inflammation and DNA damage…. DNA damage in peripheral immuno-competent cells, indeed, most likely resulted from an increased generation of RONS due to initial systemic inflammatory responses or the delayed inflammatory processes in response to muscle damage (Fig. 1). [3]

What About High-Carb Diets?

Do high-carb diets contribute?

During strenuous exercise mitochondria produce oxidation products:

The mitochondrial electron transport system can trigger the formation of superoxide leading to increased production of H2O2 by superoxide dismutase [49], [50]. [4]

In a normal person at rest, about 1-2% of the oxygen utilized by mitochondria ends up in superoxide. [4]

Before we go further let’s take a brief detour into mitochondrial chemistry: specifically, something called the electron transport chain.

Here’s a stylized view:

Source: Wikipedia.

The main point for our purposes is that there are two points of entry into the chain, one that goes through complex I and one that bypasses it.

Glucose metabolism favors entry via complex I, while fatty acid metabolism is relatively more favorable to entry via complex II. Quantitatively, glucose metabolism produces 5 NADH molecules (entering at complex I) for every one succinate molecule (entering at complex II), while fatty acid metabolism produces only 2 NADH for every one succinate.

High-carb dieting tends to habituate the body to metabolism of glucose. Therefore, it increases utilization of complex I.

This is significant because complex I is vulnerable to production of excess oxidative stress under some circumstances.

In principle, every mitochondrial complex has the potential to operate cleanly with minimal production of superoxide. However, if mitochondrial function is in any way impaired, so that operation of a complex is inhibited, then ROS production can rise substantially.

If for some reason electrons cannot flow properly through the electron transport chain, then they leave as superoxide:

One factor which may sensitise cells to increased DNA damage is impaired mitochondrial function [74]…. Reduced electron flow through the mitochondrial respiratory chain, particularly through the inhibition of complex I or complex III, favours the enhanced production of superoxide and H2O2 [75]. Together, with the age-dependent increase in oxidative stress and decline in NAD+ and ATP content, we found a tendency to the reduction in the activity of the respiratory complexes with age in all organs. Sipos et al. (2003) showed that mitochondrial formation of H2O2 due to complex I inhibition is more clinically relevant than ROS production due to inhibition of complex III and IV in situ [76]. [4]

What exactly did Sipos et al. find?  They state:

ROS formation was not detected until complex III was inhibited by up to 71 +/- 4%, above that threshold inhibition, decrease in aconitase activity indicated an enhanced ROS generation. Similarly, threshold inhibition of complex IV caused an accelerated ROS production. By contrast, inactivation of complex I to a small extent (16 +/- 2%) resulted in a significant increase in ROS formation, and no clear threshold inhibition could be determined. [5]

Basically, superoxide can be generated in complexes I, III, and IV. However, in complexes III and IV, there is a high threshold of inhibition of electron transport before any superoxide is produced. In complex I, there is no threshold:  even very slight inhibition will generate ROS. This means that during practical living, the great majority of excess ROS is produced from complex I.

This means that high-carb dieting, which increases utilization of complex I, will tend to generate oxidative stress if there is any inhibition of complex I.

But in endurance exercise, there is inhibition of complex I. To name just one pathway, exercise increases levels of the hormone DHEA, and DHEA inhibits complex I. [6]

It looks like high-carb diets and endurance exercise may be a bad combination.

Are Whole Grains Especially Bad?

There may be specific problems with grain toxins. For instance, wheat germ agglutinin, a wheat toxin that is very effective at distributing itself through the body through transcytosis, is able to damage mitochondria:

WGA induced a loss of transmembrane potential, disruption of the inner mitochondria membrane, and release of cytochrome c and caspase-9 activation after 30 min of cell interaction. [7]

At high doses in test tubes this can lead to cell death. It’s conceivable that at physiological levels WGA damage to mitochondria might mildly inhibit complex I and increase oxidative stress.

Of course, any deficiency in antioxidant minerals zinc and copper, which dismutate superoxide to hydrogen peroxide which is then disposed of by glutathione peroxidase (a selenium containing enzyme), would increase oxidative stress. Wheat contains phytic acid which chelates minerals and reliance on wheat as a calorie source may impair antioxidant status.

Conclusion

I don’t want to exaggerate the risks of endurance sports. With the exception of melanoma [8], there isn’t a clear increase in cancer incidence among marathon runners. And if this post seemed a bit tortuous, it’s because there’s no simple “smoking gun” pathway connecting endurance exercise to cancer.

On the other hand, endurance exercise is probably not as healthy, in terms of cancer risk, as shorter-duration activities. Also, the risk may rise substantially on high-carb or wheat-based diets. There are at least a few plausible mechanisms, not all of which I’ve discussed here, that might connect endurance exercise on grain-based high-carb low-fat diets to cancer.

References

[1] Vilenchik MM, Knudson AG. Endogenous DNA double-strand breaks: production, fidelity of repair, and induction of cancer. Proc Natl Acad Sci U S A. 2003 Oct 28;100(22):12871-6. http://pmid.us/14566050.

[2] Cooper MB et al. The effect of marathon running on carnitine metabolism and on some aspects of muscle mitochondrial activities and antioxidant mechanisms. J Sports Sci. 1986 Autumn;4(2):79-87. http://pmid.us/3586108.

[3] Neubauer O et al. Exercise-induced DNA damage: is there a relationship with inflammatory responses? Exerc Immunol Rev. 2008;14:51-72. http://pmid.us/19203084.

[4] Braidy N et al. Age related changes in NAD+ metabolism oxidative stress and sirt1 activity in wistar rats. PLoS One. 2011 Apr 26;6(4):e19194. http://pmid.us/21541336.

[5] Sipos I et al. Quantitative relationship between inhibition of respiratory complexes and formation of reactive oxygen species in isolated nerve terminals. J Neurochem. 2003 Jan;84(1):112-8. http://pmid.us/12485407.

[6] Safiulina D et al. Dehydroepiandrosterone inhibits complex I of the mitochondrial respiratory chain and is neurotoxic in vitro and in vivo at high concentrations. Toxicol Sci. 2006 Oct;93(2):348-56. http://pmid.us/16849397

[7] Gastman B et al. A novel apoptotic pathway as defined by lectin cellular initiation. Biochem Biophys Res Commun. 2004 Mar 26;316(1):263-71. http://pmid.us/15003540.

[8] Ambros-Rudolph CM et al. Malignant melanoma in marathon runners. Arch Dermatol. 2006 Nov;142(11):1471-4. http://pmid.us/17116838.

Leave a comment ?

50 Comments.

  1. Great summary Paul.

    As you say, nothing set in stone on this issue, but there is some smoke there nonetheless.

    There needs to be a distinction between undertaking training/racing that is required to reach a peak performance and that which is optimal for health. Unfortunately, many athletes make the mistake that because they are athletes, they are automatically optimally healthy. I’ve worked with plenty of cyclists who are plenty fast on a bike, but off the bike, have some serious health issues going on.

    Likewise, non-athletes also tend to view athletes as being optimally healthy, and in particular, less fat than they might be, and so aim to emulate their training and lifestyle. Lance has some above-average ability on the bike and beat cancer, so if I follow the exact same programme as him, then I can be a velociraptor on the bike, and I’ll be impervious to cancer!

  2. There seems to be an interesting parallel here between the mitochondrial damage you describe and the diseases that benefit from forcing the body to, I presume, bypass complex 1 through a ketogenic diet.

    However, if the running man hypothesis is true, man evolved to be endurance athletes.

    One thing that modern athletes do that traditional endurance athletes would not is attempt to completely fuel themselves via carbs. They continuously eat carbs, forcing glycolisis, even during short races that could be fueled via fat and glycogen.

    Could this contibute to mitochondrial misfunction?

  3. Great post! Tuck – I always wonder about our extreme ultra running past – 1) without sports bras I don’t see it 2) toddlers are freakin’ heavy to carry, and they will “run” themselves at exactly an adult walking pace – but, yes there is the whole Achilles heel thing and our hairlessness etc. that is compelling – but running a 10 min mile if you are an HG persistence hunter, stopping to look at droppings, to scoop a handful of water from the stream, etc. – seems to me your heart rate might stay in a more reasonable range than the modern marathoners

  4. Hi Jamie,

    Keith Norris had a nice plot on this topic: http://theorytopractice.wordpress.com/2011/05/02/chasing-performance-at-the-expense-of-health/

    Hi Tuck,

    I do think a high-fat diet would be better for the mitochondria, and produce less stress.

    But antioxidant status, and infection status, are probably even more important.

    The wild card may be food toxins, like WGA … Most scientists would not believe these are significant, but I think they must be somehow — we just don’t know the mechanisms!

    Hi Emily,

    The toddlers would indeed have a hard time catching the pronghorn antelope … unless it wanted to play!

  5. Just posting that I am a distance runner, and while I know it is not optimal for health, I do it for competition (also I am on a college team). And yea it does get boring sometimes, but I guess deep down I love running and competing. As far as diet goes I try to follow paleo/primal/perfect health diet as much as I can. (trying to limit polyunsaturated fats, eating safe starches, meat/fish/eggs/some nuts/cheese). Overall I feel great and have a lot of energy, I just hope I stay healthy into the future. I don’t plan to run all my life, but I do want to do some marathons after college… (and fast ones too!)

  6. Hi Max,

    I ran 60 miles a week in college. Probably just as well I hurt my knee as a senior (foolishly running down a steep hill with tall grass and landed in a rabbit hole).

    I don’t think it’s that dangerous on a good fatty diet with good nutrition. Good luck!

  7. Emily,

    Take you car out and put it in first gear and drive it on the red line for a couple of hours… then do this day after day. It might cope initially, but it is going to show signs of premature wear and tear and will blow to bits long before it otherwise should. I can’t see the human cardiovascular system being much different (allowing of course for its ability to undertake a degree of healing).

  8. Whose body is more habituated to fatty acid metabolism? Someone who eats 100g per day of carbohydrate and does no exercise, or an endurance athlete who eats 300g per day of CHO and burns 1200 calories with physical activity? Endurance exercise is a strong promoter of fatty acid metabolism, as well as being able to generate the same ketone levels as a low-carb diet.

    You can also not extrapolate studies based on running to other non-impact activities (like cycling). As one example, the studies that found greatly increased CRP in runners (indicating inflammation) was not confirmed in cyclists.

  9. Paul,

    good article. I wonder how this relates to intense resistance exercise where the duration might be much shorter but the resulting inflammation due to muscle damage might be even higher and glycogen depletion is similar. Or is the fact that it almost solely runs on the anaerobic system and like I said for a much shorter time less harmful? I mean, no oxygen – no oxidation, right?

    Jamie,

    good point! “Fitness” and “health” are used interchangable when they are two seperate entities in reality! See D.McGuff’s BBS for a reasonable definition of both.

    Michael,

    the cyclist-thing makes sense as cycling is relatively uniform concentric only exercise without sudden impacts (no hitting the floor) and eccentric exercise (no downhill “breaking”) like in running.
    Swimming may fall in the same category.

  10. wonderful article.
    thanks!

    i read somewhere that cyclists have an unusually high rate of testicle cancers….

    regards,

  11. Great article, I think there is a correlation to the high carb intake for distance runners and athletes. As a runner (not a marathoner) and cross country skier, I used to take in waaay too many sugary energy drinks like gatorade (ugh!) and it ruined my health. Now I still do the same types of workouts on a Paleo diet and my health is fantastic. I recover and sleep better, my body handles stress better. I definitely think the correlation is the sugar.

    Keep up the great posts!!

  12. Is there a general guideline for what qualifies as endurance vs moderate exercise?

  13. Dear Paul,

    It will be much better for your site in google and other search engines if you set permalinks in your urls.

    To do that, go to your wordpress dashboard, click settings on the lower right side, then click permalinks under sttings, check off day & name, then save, all done.

    By the way, great blog!

  14. Michael,

    Good points … The article I cited did say that muscle damage was a key part of the problem, and the greatest oxidative stress was >24 hours after the event when muscle damage was being repaired. Maybe the pounding runners take does a lot more damage.

    That would fit Pam’s point about testicular cancer in cyclists — maybe the site of the pounding is different! Or maybe heat is also a factor in tissue stress.

    Hi Franco,

    I think resistance exercise should cause much less stress for the reasons you say … but the review article I read didn’t say anything about strenuous but brief resistance exercise.

    Hi Amy,

    I do think a fatty diet should be much safer.

    Hi Lisa,

    Guidelines are very “general.” Natural metabolic breakpoints are at about 10 seconds (transition anaerobic to aerobic) and at about 1 hour (glycogen depletion and transition to fatty acids and/or glycolysis), but if muscle damage is the key, a simple feeling of discomfort, stiffness, or tiredness may be the best indicator. Exercise should be tiring but not exhausting or painful. For a runner, your gait should not be disturbed.

    Hi Chris,

    I tried to make the change but all my links were broken, it didn’t recognize links by post ID anymore. I’m going to upgrade WordPress soon and I’ll see if the new version has fixed that.

  15. Paul,

    That’s interesting!

    One thing that caught my attention was that marathon runners had an increased risk for melanoma, since heavy occupacional exposure to sun is associated with a lower incidence of melanoma.

    http://www.ncbi.nlm.nih.gov/pubmed/9335442

    But, then I remembered Dr. Kurt Harris saying in his interview for Chris that he does not supplement vitamin D and that 1,25(OH)D3 (calcitriol) was the active form and the one that really matters. What occurs with 1,25(OH)D3 when marathoners are doing their usual trainning? It decreases!

    http://www.ncbi.nlm.nih.gov/pubmed/8481833

  16. Hi Mario,

    Both 25OHD and 1,25(OH)D3 are active, and I disagree with Kurt that 1,25D is more important. However, 1,25D is the one that is responsible for calcium regulation. So marathoning might induce a calcium deficiency.

    There are associations between calcium deficiency and colorectal and breast cancers, see http://www.ncbi.nlm.nih.gov/pmc/articles/PMC2790094/?tool=pubmed.

    But this mechanism seems a bit tenuous to me. Perhaps it plays a role.

  17. Lucas Tarfur posted on substrate oxidation the other day (http://www.ketotic.org/2011/05/bioenergetics.html). Although I think the evidence is in strong favor of fatty acid oxidation, theories about ROS production and health/aging aren’t airtight.

  18. Paul, Thank you very much for this post. I too am a long distance runner who has pondered this question since I started reading about real food diets about five years ago. On the one hand, I understood high carb and fructose diets, especially ones based on bread and pasta and sport drinks, were not healthy. On the other hand, runners were told to carbo load before, during and after long runs. I cancelled my subscription to Runners World after finally running out of patience reading their health and diet recommendations. I also recall vividly reading Cordain’s Paleo Diet for Endurance Athletes and thinking his advice just didn’t make sense. Afterall, if excessive carbs are bad, why consume them when running. My diet for the last three years has essentially mirrored the PHD, and my long runs are done in the mornings on empty stomachs. My ketoadaption took about 3-4 weeks, but that was all. Still, I wondered if running 30-50 miles a weeks was healthy. After reading Body by Science in January, I decided to find the least amount of exercise that would still allow me to run at the same level I had when consuming carbs. Right now, I do one 10 minute workout per week with weights and one 10-15 mile run on the weekend. Guess what, my running has not suffered and I feel much more rested. Still, the question for me was not is running marathons healthy?–I don’t believe it is–but whether running was unhealthy. My belief (hope?) has been that the high carb inflammatory diet in combination with the stress of running was the problem and that while running may be short-term inflammatory, following a very non-inflammatory diet reduced my chances of hurting myself. Your post makes me think my reasoning is sound. What we really need, however, is sound research that looks at similar groups of runners who follow very different diets. I’m not holding my breath that the public health community is going to produce such work. I would add finally that I have yet to encounter a long distance runner who takes me seriously. Again, thanks for the post.

  19. This is very interesting. I wonder how much diet factors in all of this…

    Tour de France riders sometimes consume as much a 9000-10,000 calories on race days! (Not to mention the more frequent training days) And the majority of this comes from carbs, like Tuck mentioned earlier.

    Here’s a list of what constutites a race-day menu for a major team on the tour. So much sugar, so much wheat, so many red flags! I wonder how many people model their training diets on this?

    http://sports.espn.go.com/espn/page2/story?page=stein/090701

    This can’t be good for you. So I wonder if diet is the major factor in the endurance excercise-cancer connection? Talk to any athelte amatuer or professional and they’ll extol the ‘benefits’ of high carb eating becasue of their training demands it!

  20. Paul,

    Great line of inquiry here. I am curious at what point resistance exercise might start to cross into excessive oxidative stress.

    Even if an individual only lifts weights 2-3 a week, fairly briefly, they could cause significant amounts of fatigue and soreness depending on the amount of weight and the exercise chosen. Could this stress be made worse by excessive protein consumption?

    *****Also, a question about an earlier post of yours that I’ve been meaning to ask. You stated earlier in reference to Melanesians and their low protein diet, that less protein may be required due to a lower toxin load in their diet. Could you expound on this?

  21. @Emily: The most fascinating part of the “born to run” hypothesis is two-fold, as regards women: running performance between men and women starts to equalize and the distance increases. Men are much faster sprinters, but only slightly faster endurance runners (distances greater than marathons).

    The other one concerns the jog bra issue. If you run in your barefeet, there’s much less bouncing, of everything, then if you’re running in sneakers. Jog bras are an response to sneakers, not to running.

    Prof. Lieberman has a whole list of adaptations that only make sense if we’re endurance hunters, and can demonstrate a reliable human ability to run down most large, edible animals. Even horses (which explains how humans domesticated the horse).

  22. Hi john,

    Yes, not airtight. When conditions are right both glucose and fats make fine energy substrates. In pathological conditions the analysis becomes complex. But it does look good for fats.

    Hi Richard,

    That’s very interesting. Body By Science Running!

    I think running is healthy, as long as it doesn’t overly stress the body. If you feel good afterward, tired but good, then I think it’s healthy. If you feel run down and sore, then I think it’s unhealthy.

    Best, Paul

  23. Hi Robert,

    Very interesting menu! It’s certainly not healthy. Is it even race-day performance maximizing? I have trouble believing it. There must be diminishing returns to carbs relative to fat at some point.

    Hi Mike,

    It’s a good question. I haven’t really looked into the resistance exercise literature, so I’m ignorant on this one. I’ll keep it in mind for blog posts.

    Hmmm. I’m afraid I don’t recall saying that about the Melanesians. Do you have a link or recall the context?

    Hi Tuck,

    Interesting about the sports bras, perhaps it will help convert my wife to Vibrams.

    I’m having a hard time imagining humans capturing horses by out-running them. I would imagine herding them with dogs into corrals was the key. Other strategies that might have worked could include providing food, especially in times of drought; or capturing and healing injured or sick horses. But persistence running is possible I suppose.

  24. Jamie, I’m pretty sure I came with a warranty for 70 years… not sure about the sturdiness thereafter 😉

  25. Tuck – Hmmm – I run barefoot with a midsole stride and I still need my champion… also breastfeeding makes a HUGE difference as well with respect to comfort, especially in the first six months of a baby’s life. I’ve also tried to go fast with a baby in a sling (and toddlers hanging on) and it is not easy, though I imagine would become easier if you had to do it. However, I have read Born to Run and I do find it amazing (though not surprising 😉 ) that so many more women (percentage wise) complete the ultramarathons than the men… truly an equalization of skill at that level.

  26. Paul,

    On the issue of toxins/low protein and melanesians –

    I may have been reading into your post too much (or I remembered it incorrectly) from Jan. 27 where you said:

    “It’s true: Kitavans, Tokelauans, and other Melanesians eat high-carb and low-protein, yet they’re noted for “extreme leanness.” [3] Why?

    Well, first of all, the Melanesian islander diet is a variant of the Perfect Health Diet: it is entirely free of food toxins.”

    It appears you were saying that being free of food toxins just allows one to be lean on a low protein diet.

    But would you endorse the further proposition that being free of/having few food toxins would lower the body’s requirement for protein? It just struck me that the citation to melanesians eating only 3 to 10 percent of daily calories as protein was exceedingly low. I would be concerned with losing athletic performance at levels below 10 percent.

  27. Hi Mike,

    Ah! My belief is that food toxins cause obesity and so a diet free of food toxins should keep people lean regardless of macronutrient ratio. It doesn’t matter that carbs stimulate insulin or that a low protein diet lacks the satiating factor of protein.

    No, I don’t think lack of food toxins affects protein requirements, except indirectly (eg a toxic diet might increase cysteine requirement for glutathione production / detoxification pathways).

    I do think people can adapt to and live a long life on a 3% protein diet, but it will limit muscle size and strength. So not good for athletes.

    Best, Paul

  28. @Paul “I’m having a hard time imagining humans capturing horses by out-running them.”

    Dan Lieberman at Harvard is doing most of the research on this, here’s an explanation of how humans can out-run a horse:

    “Horses can easily outrun humans with a maximum
    gallop speed of 8.9 m/s for a 10 km race, but their sustainable galloping speed declines dramatically for runs longer than 10–15 min; in repeated runs over long distances, horses are constrained to about 5.8 m/s for approximately 20 km per day, above which they can sustain irreparable musculoskeletal damage (Minetti, 2003). By these standards, human ER capabilities are quite impressive, and explain why humans can sometimes best horses in long distance races such as marathons (e.g., http://www.man-v-horse.org.uk/).”

    http://www.fas.harvard.edu/~skeleton/pdfs/2009a.pdf

    He’s got some pretty interesting notions on the paleo diet and modern human health, as well. You and he would probably have a fascinating discussion.

  29. Franco,

    Whilst cycling is concentric in the legs (if we are talking road/mountain – track is a different story due to the fixed gear), there is still a degree of heavy muscular loading and eccentric loading through the upper body at least. When you are driving big gears up hill for long hours, or riding off road, the upper body musculature is heavily involved and could add to any total oxidation levels. Granted however, impact sports such as running is likely to be significantly worse.

  30. Interesting link on what the cyclists from the Tour de France eat. I can’t imagine it being easy to consume close to 9000 calories on a paleo type diet. Not saying it’s impossible, but all that fat will have me in the toilet the whole day.

  31. Jamie,

    the last time I was biking for longer distance was maybe 20 years ago. But now that you say it, I remember the up hill stress. I don’t understand the track comment (never did that). Is there active pulling up of the lower foot? For me biking is push only, not?

    Tuck,

    no doubt some people can do that (San) but I really don’t feel any desire to do any long distance sports – let alone outrun horses! And I was always like that, long before pickung up lifting weights. I do and was always prefering/enjoying brief bouts of strenous exercise and this despite not beeing of the stocky, naturally muscular bodytype.
    Maybe I’m just lazy… 🙂

  32. Robert, a paleo diet does not necessarily mean a high-fat diet.

    Also, what about the difference in effects on “endurance sports” like soccer and lacrosse and hockey, that don’t have the monotony of marathon runners or clycing? Perhaps there is something to a different mental state during the exercise. In running, it’s just to “keep going,” whereas the others it’s to “score” or “steal” or “block,” etc. I wonder how much of a mental aspect there is to all of this?

    Also, there’s probably something to the massive amounts of cortisol that prolonged endurance running or cycling brings about. I would suspect that soccer does not produce such a massive increase in cortisol levels as does strict endurance exercise. ALso, maybe the individual nature of the sport/activity has something to do with it? I just feel like it’s important not to neglect the mental aspect of it all.

  33. Nelson, you make a very good point. A lot of it has to do with mentality. As a soccer player I feel I perform my best athletically when I am motivated to defeat the opposing team. On days I am not mentally wired my performance suffers tremendously. I would imagine running monotonously with no clear goals could be potentially stressful. In paleolitic times exercise wasn’t done without reason, they did it for survival.

  34. Hi, I tried looking for some sort of relevant post to put this under, and I hope you don’t mind this off topic post, but I saw this the other day and thought you might find it interesting.

    Also, the point the guy brings up is interesting. As men get older should they look into hormone supplements?

    http://video.foxnews.com/v/4694717/get-healthy-at-any-age/?playlist_id=87485

  35. Hi Craig,

    Personally I wouldn’t try hormone supplements — certainly not growth hormone, and would be very cautious about testosterone. Those can easily backfire.

    I think the doctor gave good advice. Eat well and exercise and your hormones will stay good for a long time.

  36. Google scholarly

    On an antioxidant-and-carbohydrate tangent, I’d be interested in your opinion of the recent surge of research on hydrogen as an antioxidant. Hydrogen has remarkable and diverse effects as a therapeutic agent (consumed as “hydrogen water”), and it’s produced in the gut by fermentation of non-digestible carbohydrates. Here’s a recent review:

    http://onlinelibrary.wiley.com/doi/10.1111/j.1440-1681.2011.05479.x/full

    Excerpt:

    “Recent evidence indicates that hydrogen is a potent anti-oxidative, anti-apoptotic and anti-inflammatory agent and so may have potential medical application. The present review evaluates the concept of ‘hydrogen resuscitation’, based on knowledge that hydrogen treatment effectively protects cells, tissues and organs against oxidative injury and helps them recover from dysfunction.”

    Google Scholar, “hydrogen water”, pulls up many papers.

  37. The Myth of Cardiovascular Training | Critical MAS - pingback on August 5, 2011 at 2:10 pm
  38. It is really a nice and useful piece of information. I?m satisfied that you shared this useful info with us. Please stay us informed like this. Thank you for sharing.

  39. This is a test comment, hello world! Regards. . .

  40. hi. im just curious. this is the first time i read on the internet that high carb diet can cure fungal infection. it’s a common knowledge that too much sugar can induce fungal infections so why are you thinking otherwise?

    i have systemic candida, so what should i eat everyday? i do intermittent fasting daily and only eat rice as my carb. i do sometimes eat pasta made from wheat. is that ok?

    itinbcalvo@gmail.com

  41. Hi itin,

    It’s not a high carb diet that you want, it’s a moderate carb diet. 400-600 calories per day, 20-30% of calories as carbs.

    You also want to avoid fructose. So no sugar.

    Rice is a good carb. It’s best to avoid wheat.

    Best, Paul

  42. Curious, do none of the sprinters or practitioners of other sports ever develop cancer?

  43. Hey Paul, interesting article. However, most studies show that endurance athletes are able to manage the oxidative stress from their workouts and training. There’s even a decline in DNA damage after Ironman triathlons in well-trained athletes. I went into more detail in this article:

    http://impruvism.com/exercise-oxidative-stress/

  44. Shieldmaid’s Guide to PaleoWorld | Shieldmaid - pingback on May 31, 2013 at 7:59 am
  45. i dont think that endurance exercises can lead to cancers of any sort because when we are doing endurance worlout we are putting our heart into pressure which can actually promote good blood circulation of our body. am i wrong?

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