Running from the proof: correlation does not mean causation

Gary and me on our front porch.  Photo by MD Eades 8/13/2008

Gary and me on our front porch. Photo by MD Eades 8/13/2008

A couple of days ago Gary Taubes, who was visiting family in Los Angeles, drove up to Santa Barbara, and he, MD and I got together for a long lunch. We talked about all the things we always discuss, most of which have nothing to do with nutrition or nutritional science. But, as always when we get together, talk did turn to science and the sorry state of nutritional science in the world today.

We discussed a Stanford study that was recently published in the Archives of Internal Medicine demonstrating that those who are runners live longer and have less disability. The paper proves absolutely nothing, yet an enormous number of people, many of whom should know better, profess that this study is the smoking gun that ties exercise to longevity and health.

The researchers sent questionnaires to 538 members of the 50+ Runners Association and healthy controls from the Stanford area who were 50 years old or older in 1984. By 2005, 284 runners and 156 controls had completed the 21-year follow-up. After crunching the data, the researchers found that more than double the number of controls had died as compared to the runners and that the total disability score for the controls was much higher (i.e., they had a greater degree of disability) than for the runners. The conclusion as stated by the authors:

Vigorous exercise (running) at middle and older ages is associated with reduced disability in later life and a notable survival advantage. [My italics]

The conclusion of this study, which is absolutely accurate, is that running is associated with longevity and reduced disability. The two are associated or correlated. The study does not prove that running increases longevity or decreases disability. Correlation is not causation. But you wouldn’t know that from the press coverage of this study.

If you run a Google search, you will find the study reported as proving causality. See here, here and here for just a few instances.

Let’s explore this study a little because it provides a good example of what these kinds of studies show and what they don’t. And why we should never rely on association or correlation studies as proof of anything.

First, in the USA (and in other countries as well) it is a given that exercise is good for one. We believe that exercising will make us live longer. And a lot of us believe that exercise will make us fitter and have less disability as we age. When we see a study that seems to prove this, we accept it without batting an eye. Even though the study shows no such thing. We are culturally primed to accept scanty evidence to prove what we already believe about exercise.

Let’s assume that our cultural dogma was that exercise was unhealthy and that those who did vigorous exercise were killing themselves. We used to kind of think that in this country. I’ve often heard it said that someone (who was employed in a physically demanding job) had worked himself to an early death. So let’s suppose that were our cultural default, and we are looking at the same data as presented in this study. We would ‘know’ that exercise isn’t good for us, and, in fact, is probably bad, so we would look for different differences between the two groups. We might find that the group of runners drank way more water than the non-runners. And let’s assume for argument’s sake that our culture believes that water consumption is good and healthful. This same study data could then have been presented in terms of increased water consumption negated the negative effects of running, and even allowed runners to live longer than non-runners who drank less water. What we look for in these studies is culturally driven.

Were we in France – where I’ve yet to see anyone jogging – we might get a totally different take. We might have studies showing that men who have mistresses (and keep them well occupied) live longer than men who don’t. So therefore having a mistress leads to longevity…? (Probably not in my case, especially if it were discovered.)

Studies showing associations or correlations between between activity A and result B do not mean that A causes B. Yet it is extremely easy to be beguiled into believing that A causes B, especially if it makes sense based on our belief system. It doesn’t make logical or scientific sense to jump to that conclusion, although far too many people do.

I suspect that there are a number of people reading this post right now who firmly believe – despite all I have written above – that the study in question really does prove that running improves longevity because it seems to make so much sense. But let’s explore a little further.

We don’t know and can’t possibly determine from this study whether it is the running that increases longevity or whether there is some facet of personality or physiology that drives one to run that increases longevity. Maybe people who are destined to live longer take to running or other forms or aerobic exercise. People who are depressed typically have shorter lives, and people who are depressed tend not to join groups or exercise. Perhaps a number of the people in the control group are depressed, leading to an increase in early deaths in that group. It could be that the people who have the time to join a running group and spend the time running are more financially stable and are happier. Both of those conditions are correlated with longevity. There are far too many factors separating the two groups to dissect out the one and attach the benefit to it. But our culture firmly believes that exercise promotes longevity, so this experiment seems to bear that out, and most people accept it without looking to deeply.

One of the commenters on this blog gave a good example of this in a comment today. Let’s say we have a study showing that red cars are involved in more accidents than white cars (which may be true, for all I know.) Does this prove that red cars are more dangerous? Or does it prove that drivers who have the mindset that motivates them to choose red cars are less careful drivers? Or both? Or does it prove the opposite about white cars? You can’t tell.

If what I say is true, you make ask, why even do these kinds of studies if they have no value? The answer is that they do have value. They allow scientists to derive hypotheses that can then be tested. But often the rigid testing required for proof is impossible, so people who should know better fall back on these kinds of associative studies as proof since real proof can’t be obtained. Why not? Let’s take a look.

If we wanted to firmly establish that running increased longevity, we would have to do the following study. We would have to select a large group of subjects who are all of the same age and level of health. We would then have to randomize them into two groups: one a running group and the other the sedentary group. We would have to force the people in the running group to run and force the people in the sedentary group to be sedentary. Then we would have to follow these two groups for 21 years. If the runners then substantially outlived the non-runners, we might have a case that running promotes longevity. But until we do this, we can’t state that we have proof. You can see the immense difficulty involved in performing such a study. You can’t simply randomize someone who isn’t really driven to run into the group of runners and expect that person to run daily for 21 years. Yet that’s pretty much what you have to do to establish causality.

The moral of this story is to view these studies for what they are. Interesting but not proof.

Please note: I reserve the right to delete comments that are offensive or off-topic.

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42 thoughts on “Running from the proof: correlation does not mean causation

  1. I’m a lousy excuse for a scientist, which is why I read your blog for explanations about studies. But shouldn’t they have included some dead runners in their survey? The ones who live to tell the tale aren’t the whole story! What about the ones who got hit by cars or died of cardiac arrest or drinking too much water on a run?

    Just another reason such studies aren’t valid as measures of causality.

  2. I do believe that red cars receive more traffic violations than other colored cars, so certainly, they get the attention of the police more often than not (this information is old and may be outdated: traffic school in So Cal in 1980s, when I drove a red car).

  3. I had to do running while in the military (and I hated it) and I now have a 10% disability because running caused some kind of damage to my left foot/ankle. When I think of running, I think of pain. It is not an exercise that is easy on the body. Maybe it’s great for the heart, but certainly not for the legs.

  4. Another anecdote to add to Angel Q’s:
    My husband, who served 20 years as a USN officer, was required to participate in annual physical fitness qualification exercises, which included running a specific distance in less than a specific time, has now undergone bilateral hip replacements under the age of 55 and is disabled with spine problems.
    Was it the running he was forced to endure under less than optimum pavement conditions, or the repeated HIGH “G” force landings and takeoffs from carrier operations that contributed to one or both? No one can tell him definitively, but the USN pays him for 40% disability and Social Security considers him totally and forever disabled from holding any “significant wage earning position”.

    I avoid “cardio” exercise like the plague.

    Martha

  5. Just a little short of 70, I get a great deal of satisfaction out of sprinting about a mile a week. Should my health give out obviously I would have to quit. So one incontrovertably true statement is that while you are healthy you may be able to run. When you quit being healthy you no longer can run. This logically implies that running is dependent upon good health. I suspect that sprinting does some good things for me, but that proves almost nothing.

  6. I was getting ready to blog about this myself.

    What stuck out to me about this study besides the socioeconomic marker involved was that the researchers started out with people who were runners at age 50. This selection criterion in and of itself was enough to select a group of above average health. By age 50 many of us have already developed health conditions and joint problems that limit our mobility, so while we might exercise, we probably would not choose running as the way to do it.

    Had they used the person’s buying a gym membership instead of joining a running club they would have been likely to see a very different pattern over time since people with a much broader range of health join gyms.

    More importantly WHY hasn’t anyone noticed the study in last month’s Diabetologia which proved that eating whole grain bread raises blood sugar in people with diabetes just as high as eating white bread. There was not a single article about this finding, though it blows away the entire “Low GI’ fad argument.

    The Diabetologia paper is just one of many that never see the light of day because such papers don’t confirm the bias of those selecting which papers make it into the media.

  7. Thank you for publishing a good piece that explains this point. It is something that is overlooked regularly by the media – in my view usually willfully – and gives ammunition to the kinds of people who would go out and spray paint red cars in the name of road safety.

    This concept should be taught in schools as a separate topic, as the world would be a better place if it was fully understood by all!

    Methuselah
    Pay Now Live Later

  8. Maybe this study just shows that people who join clubs live longer.

    There is as great a possibility of that as there is that the study shows running increases longevity.

  9. Sorry, I misremembered which Journal published the bread study:

    It was Diabetes Research and Clinical Practice

    “Dietary Breads Myth or Reality?”

    Volume 81, Issue 1, July 2008, Pages 68-71

    I removed the link because it didn’t work.

  10. HI, Jenny. I need to point out that your supposition is incorrect (and so is Dr Eades’ by implication as well) on whole grain bread. Whole grain bread is not necessarily low GI just because it’s whole grain. Any GI tables will show that. That’s a common misconception, which has replaced the previous misconception that complex carbs are low GI and simple carbs are high.

    Saying that whole grain is low is the worst misstatement that registered dieticians repeat almost daily as guests on tv shows. Many docs, too.

    Whole grain bread is not low GI when it is made by modern high speed rollers which produce a very fine powdered flour. The amylase enzyme can get at the starch easily. But coarse *stone ground” grain bread is low(ish) GI. It takes longer to wear down, so to speak. The coarse is more rare. People seem to prefer the fluffier fine type.

    This is not just a theory, it is an observable phenomenon, to anybody with a glucose meter. When my father had lymphoma, he was on 60 mg prednisone for many weeks, on more than one occasion (usually for secondary thrombocytopenia). Being on a high dose glucocorticoid, the resulting drug-induced glucose intolerance made the postprandial elevations exaggerated – depending on the food. So it was easy to see, time and again, either way. When I was overseeing his diet, he never needed a single insulin shot. When he was in the hospital on an “expert” created diet, then BAM! Insulin every time.

    There are many things about GI that are counter-intuitive. These reasons might tend more toward theory as to the *why*, but seem valid. For example, prunes are low but raisins are high. Why? Prunes have soluble fiber. Put some metamucil in a glass of water and let it sit to see the gel like arrangement that results. Insoluble fiber doesn’t affect GI much.

    Some rice is high, when it is mostly amylopectin starch. But other rice is low, if it is mostly amylose starch. (Being whole grain rice doesn’t matter much.) Uncle Ben’s converted rice (not whole grain) is low. It’s just a fact. Usually short grain rice is high, but can vary by region.

    White spaghetti is low GI – as is anything made of duram semolina wheat. (Canned spaghetti is high.)

    What about table sugar? Fructose is at 20 and glucose of course is 100. So then you’d expect sucrose to be right in between, and in fact it’s usually measured at around 55. That is not high GI, more like medium or high-medium. (But IIRC sucrose is more insulinotropic than it’s GI would suggest.)

    So blood glucose will respond to average “whole grain” breads the same as to white bread. It seems odd to me that anyone would even do a study on that.

    Where do the figures in GI tables come from? From studies! Give food to groups of subjects and just measure BG.

    The pioneer in this was mainly one Jenny Brand-Miller, from Australia.

    Why do some people get agitated sometimes about GI (which I’ve experienced), as they do about Atkins? It’s not just some trendy new weight loss diet, it is simply observable phenomena.

    I avoid the entire issue by not eating bread (of any kind), rice (of any kind) and pasta (of any kind). This doesn’t mean that I never touch these foods; it simply means that I rarely do.

    I don’t like the glycemic index idea (which, BTW, was pioneered by David Jenkins from Toronto, not JBM) for a number of reasons, not the least of which is that it encourages the consumption of fructose, a low GI sugar. You can read the other reasons I’m not crazy about the idea of the GI in this post.

    Cheers–

    MRE

  11. As a former national-class marathon runner who fell apart from the training, I have been skeptical of these health claims for 20 years and I write about it frequently. I have seen too many runners and triathletes of all abilities develop not only the obvious joint issues, but serious heart problems (the exact opposite of what the current literature would predict). One of my theories is that it is the almost-obligatory high-carb diet that leads to inflammation throughout. Some can contain it – others can’t.

    Of course, if you eat low-carb you can’t “run” long every day. And that’s a good thing, but you can certainly walk forever. I think that’s what our genes want us to do: lot’s of very low level aerobic stuff and the occasional all-out ATP-only “sprint for your life.”

    http://www.slowtwitch.com/mainheadings/features/health_doping_slowtwitch2.html
    http://www.marksdailyapple.com/chronic-cardio-2/

    On a final note, to follow Gary’s well-thought reasoning, maybe running doesn’t make you thin, but being thin (with lowered risk for everything already) predisposes you to being a runner. To add to your study parameters, you’d have to take a group of predisposed runners and force half not to run and the other half to run. Then you’d have to take predisposed sedents and force half to run and half not to. OTOH, maybe this needs to be a double blind where no one knows whether they are running or sedentary……

    As always, thanks for your input, Mark. I especially like the suggestion of the double blind study of seds and runners.🙂

  12. Did they consider that maybe some of the non-runners were non-runners because of health issues? So maybe those health issues led to their demise rather than “not running”? Instead, the media probably just assumes all the non-runners were “typical fat, lazy Americans” and that was their reason for not running. I used to run and would love to be able to run now but chronic health issues make it difficult for me to exercise. I am not overweight but I am almost 50–as another commenter stated, many people by 50 have health issues that prevent running. And running is quite hard on the body. Even when I was young (20), I got injured from running (stress fracture).

  13. Which one is you in the picture? Not having seen a picture of either of you, I can’t tell. I tried clicking on “More about” under the “About” section in the upper right to see if there was a picture of just you but I get a “404 page not found”.

    I’m the good looking one.

  14. Maybe the whole purpose of such study makes no sense. True, it would be impossible to set up a 21-yr follow up of randomized people just to see if exercise causes increase in longevity. However, it is important to know if exercise is good for one’s health. So, I could easily reason that provided that i don’t do things like crossing the highway where I shouldn’t do it, or putting myself in situations that are life threatening (situations where I have control, that is), then doing anything that keeps my body from getting ill would not accelerate my death. Sure, I’m not asking questions about longevity, but I’m interested in doing everything possible so I don’t jeopardize my life. Okay, back to exercise. One thing that could help me NOT dying too soon is not to get osteoporosis (just an example), and if a good measure of osteoporosis is a change in, say, bone mineral density in certain areas (spine, hips, legs, wrist, etc.), then a study could be conceived to test if exercise (running or other type of exercise) has what kind of effect on bone mineral density. If osteoporosis increases the incidence of death, then one could think that anything that prevents osteoporosis would also prevent death related to that. Sure… one can always die from falling of the treadmill, or by not being careful with the barbell when is above our chest, but that’s another story.

    My point is that perhaps the way some studies are conceived is what not only makes them impossible to perform (or fund) but rather impractical. Perhaps such studies can be broken into key pieces (actually shorter studies), that can be practical. So, perhaps we can’t show that A causes B, but if C, D, E, etc. do cause B, then any effect that A can have on C, D, and E is likely to affect B. Maybe the trick is to find all those other factors that affect longevity and then study the effect of exercise on those factors.

    The trick is in finding all those factors that affect longevity without having to resort to these sorts of studies to find them. The only way you really know are randomized controlled trials. Anything else isn’t science – it’s speculation.

  15. Excellent point. And forgive me if my comments have already been covered elsewhere; I just became aware of your blog. In any case, I think you’re absolutely right that this study doesn’t “prove” anything, it only establishes a relationship. I would suggest however, that enough studies such as this, looking at a variety of different parameters, builds enough of a case that one could draw SOME conclusions about causality, and maybe even choose a course of action based on those conclusions. For example, what if we were to add to this study another one that looks at water consumption and longevity (showing no benefit), another showing an association between endorphins and longevity (showing benefit, this time), etc. etc. and at some point a reasonable person might conclude that there’s enough evidence to decide to begin running as a strategy to improve one’s chances of longevity. Particularly if there’s no evidence to the contrary, and especially when, as you point out, the likelihood of “proof” ever being established is remote. I would propose that waiting for proof (in the scientific sense) might make for good science but poor lifestyle choices.

    It doesn’t even really establish a relationship other than in the sense that both events occurred, i.e., running and longevity. One could do all the studies you suggested, but they would all be the same. Nothing conclusive that one could hang one’s hat on.

    Cheers–

    MRE

  16. I enjoyed your interpretation of the study. I am a runner, it is part of my life, and I will run as long as I am able to. I have run 20+ marathons. Running has changed my life and made me a healthier person. Even though I run long distances, I do not believe long distance running is good for a person . I think we should be doing a variety of exercise, much at a fast pace.
    My question for you is how can we run with out carbs? If we follow your recommended diet, can a person still participate in long distance running? We have been told that a runner needs carbs.

    We have been told that the moon is made of green cheese, but that doesn’t make it so. Steve Phinney has written a nice article on the subject of low-carb diets and endurance.

  17. I am slowly but steadily becoming a fan Dr E. I just can’t help but enjoy the way you think, and relish the manner in which you tear about your naysayers. On a sideline re this post – what do you think of the theory that running causes repeated SNS overload leading to (basically) a slow death through excessively released stress hormones?

    I think the idea would be an interesting subject for study in a controlled trial.

  18. What is really frightening is the consequence this distinction has for the future of science. If the bulk of reported popular science fails to differentiate between correlation and causality, Western civilization is endangered. It is the difference between knowing reality and faking it.

    I mean, if so called scientists themselves do not or cannot grasp the difference, we are doomed to be conned and led by every witch doctor who wields political power. This was the most frightening aspect of “Good Calories, Bad Calories”. It is not that Keys was evil, but that the philosophical basis of science (and the concept of what is science) has been so undermined as to allow politics to dictate “truth,” which is so brilliantly illustrated by Mr. Taubes.

    This is why I think “Good Calories, Bad Calories” is so important. It is like “Atlas Shrugged’ of nutritional science.

  19. Dear Dr. Mike.

    This isn’t directly related to the topic at hand. But, I hope you might consider addressing it anyway, since I think it may be of interest to some of your readers.

    Would you kindly consider doing a blog about the overall health effects of regular coffee consumption? And, more specifically, on the effects coffee has on cardiovascular health and any ramifications it may have for those on carb-controlled diets?

    I know you’ve touched upon coffee in prior posts but I’ve never seen you cover it in a more comprehensive way.

    This topic comes up regularly on low-carb forums. Your take on it would be very much appreciated.

    Thanks for your blog and your time and consideration.

    Kind regards,

    Harry

    I’ve blogged about it a bit. You can find my posts by entering coffee in the search function. But here is a link to a column by Jane Brody (of all people) that does a pretty decent job of laying out where the science stands on coffee. I am no fan of Jane’s, but she is on the mark with this one. Now, if only she would interpret the nutritional literature with such clarity…

    And just for grins, here is a link to a video on YouTube of me making Cafe Americano.

  20. More and more evidence is coming up that running is bad for our bodies in more ways than just one. Yes, the more obvious way are various injuries and disabilities. The less obvious and often overlooked one is the muscle adaptation.

    Genetically, our bodies were not evolved to do repetitive long term exercise like cardio on everyday basis. Short, very intense sprints yes, but not marathon running or running 30 or 40 minutes per day or up, at least 5 times per week (like most runners do). Why not? Well, it is not natural for us and not something our predecessors used to do. And like Gary Taubes wrote, it makes you hungry. But also because the body learns and adapts. Body is always concerned with energy conservation and if you keep repeating same things for a long time, invariably finds ways how to perform those things with less energy. (You can run a longer distance but you cannot prolong it endlessly …)

    One very effective way of energy conservation is to use less muscles – so other muscles eventually atrophy and wither away. Our genes know that a smaller, less muscular body needs less energy to run the same distance. And when they see that they are going to be tortured in this same, highly unnatural way every day, they adapt. That is why marathon runners look so emaciated. And your heart is a muscle too. So running makes you heart weaker and smaller and by far more susceptible to a disease. It has also caused many a heart attack – marathon runners have been known to run 42 km and then drop dead.

    What a perversity to call this exercise “cardio”!

  21. Great thread. I am continuously amused by “the latest study” results. Because the general public has no clue about such things, they rock and roll based on the latest study.

    Proposed: People that die young are more likely to drink and smoke.

    I will bet we could prove that! But would it mean anything? Of course not!

  22. My brother-in-law took up running but also became significantly more health aware in what he was eating and lost 60 pounds. If he keeps his weight down, I expect he will count as one of those runners that lived longer and didn’t get type 2 diabetes but I think it has more to do with his improved eating habits and weight than running.

  23. This correlation vs. causation conundrum is what, I think, is responsible for the unbelievable rise in prescription medications which I believe, in many cases, does more harm than good. For example, as you have pointed out (if I understand it), the whole cholesterol myth is based on the assumption that elevated cholesterol levels associated with heart disease actually cause heart disease, which I don’ t believe is true. What is truly tragic is that hyperinsulemia actually does seem to cause disease, yet try to get tested for it….

  24. To relate back to both Martha’s and RobLL’s comments – I have recently received some extensive chiropractic treatment that has helped with my left leg – an unanticipated benefit of the treatment was the straightening out (mostly) of splayfootedness (in both feet) I’ve had at least since I was a teenager (20+ years ago). So I think that people who run regularly, and particularly people who are still running at age 50, have physiologies that are not damaged by running. Perhaps those physiologies are also predisposed to better health to begin with (in modern society). And of course, people in a higher socioeconomic class are more likely to have the leisure time in which to run regularly in the first place, can afford better food, better health care, are more likely to be exposed to beneficial health information, etc.

    And to relate one anecdote from my military experience … I started wearing a heartrate monitor when I did my physical fitness testing during my last few years of service. One test was being conducted on a hot, humid, breezeless morning in Hawaii, on a cinder running track. I was overweight and unaccustomed to running anyway (I avoided it because of my left foot problems; I used an elliptical machine for cardio), and I informed the test coordinator that I would not keep running if the monitor showed more than 200 beats per minute (bpm). This is important because slow runners are often cajoled/encouraged/yelled at to run faster, push harder, especially towards the end. Well, eventually my heartrate did get over 200 bpm, so I slowed down, but I continued “running” (a very slow jog) and got a very slow time for my run. They couldn’t accuse of me of not trying, though, which was the main reason I was wearing the monitor. The greatest benefit, for me, of leaving the military was no longer facing the dread of being weighed, measured, and enduring the physical fitness test.

    And why did I leave the military? I was kicked out for being overweight! I’d struggled for years to lose weight, and I never guessed that I had blood sugar problems because my fasting blood glucose numbers were always normal. Fortunately, I met my honey just a few months after getting out, and he reacquainted me with low-carb (I had tried Atkins several years previously and hated it, and I also did not lose much weight). He used the Protein Power approach. He also bought a blood sugar monitor and when I used it, I was shocked to see how high the readings were after I ate a “normal” (high carb) meal. I started eating low-carb and easily lost over ten pounds over the next few months with no other changes in lifestyle. I’m still overweight, but I know I am healthier because my health is improved in a number of ways; and I know I’ll eventually lose the rest of the weight.

    The military loses A LOT of excellent servicemembers due to weight issues; anyone who thinks the military lifestyle is a healthy one need only take a pass through a typical chow hall to be disabused that notion. I’m guessing the chow halls also don’t go easy on the trans-fat. Couple that with long hours and high stress jobs and one can see that only people with physiologies that are somehow immune to poor diet, long working hours, lack of sleep, and high stress are the ones who can last long enough in the service to get a pension.

  25. This entire website is rooted in lowcarb and insulin control. I assume it’s for general health and associated weight-loss. Running is the best way I know of to moderate blood sugar. Even slow jogging is using glycogen along with fatty acids. Control blood sugar through exercise, dampen insulin secretion, live longer. Or eat fatty meats while watching TV all day. Both might lead to a longer life, but I prefer the former.

    Most running injuries are the result of overdoing it. I know because I’ve had many: Achilles tendinitis, shin splints, peroneal entrapment, torn hamstring, ‘sport hernia’, chondromalacia and three fractures that occured from falls during races. I’ve been competing for nearly 20 years. I’ve never won a race, in fact my only claim to fame is the number of DFL finishes. But at age 52 I weigh less than I did in high school. (DFL means dead fu****G last)

    I believe the report says it doesn’t matter what exercise is done. After age 50, dancing is as good as running for longevity.

    You wrote:

    After age 50, dancing is as good as running for longevity.

    Maybe. But we would have to have a randomized control trial to prove it.

  26. What did you each have for lunch?

    Hmmm. Let me see if I can remember. We ate at our local Italian restaurant, and I had a tomato salad (tomatoes, olive oil and balsamic), calves liver and vegetables. Gary and MD both had Italian sausage and spinach. (Their dish was supposed to include polenta, but both asked for extra sauteed spinach instead.) We each had a glass of red wine: MD and I had Sangiovese; Gary had Chianti. We had Cafe Americanos after. MD and Gary had them decaf; I took mine full strength.

  27. I have nothing substantive to add until I’m able to read through all these comments, but I just wanted to say that it brightened my day to see this picture of my two favorite science and nutrition writers downloading on my iPhone! I used to be a marathon runner until I “saw the light”. I’m so glad to see both ME and GT responding to those headlines.

  28. Dr. Mike,
    Are not the first Low-Carb folks in the world hunter-gatherers and did they not have to
    be at least be pretty good joggers to stalk, chase, wear out and kill game for food?
    From Wikipedia:
    Hunter-gatherer fitness is a fitness concept based on the premise that people should adopt a physically active lifestyle similar to that of hunter-gatherers. Advocates argue that modern humans are adapted to a life of strenuous physical activity. Hunter-gatherers typically walk and run 5 to 10 miles per day in search of food, and, in so doing, they basically cross-train, performing aerobic, resistance, and flexibility exercises. Days of intense physical activity are followed by days of recovery. Their survival requires them to be extremely physically active.

    Not necessarily. Lions are hunters, and they spend a whole lot of time lying around interspersed with short periods of intense activity. I suspect early hunters did the same.

  29. “We discussed a Stanford study that was recently published in the Archives of Internal Medicine demonstrating that those who are runners live longer and have less disability. The paper proves absolutely nothing, yet an enormous number of people, many of whom should know better, profess that this study is the smoking gun that ties exercise to longevity and health.”

    The study proves nothing from a perspective of the science of physiology. But from a perspective of the science of psychology the fact that an enormous number of people, even highly educated people, will conclude that the study proves that exercise promotes longevity confirms what marketing science has long known – with few exceptions it is human nature to make leaps of abstraction based on superficial information that more often than not results in absurd, illogical conclusions. Worse, once an absurd conclusion has been assimilated and imprinted in the brain it is almost impossible to erase. It is a truism in marketing that ‘perception is reality’. To most people it matters not what science can prove. What they believe to be the truth is the truth in their minds. And no amount of science based debate will change that.

    Those who have followed the Beijing Olympics will know that Michael Phelps’s performance has established him as the greatest Olympic athlete in history. From a marketing perspective this gives Phelps enormous brand power and influence. What came out and will continue to be talked about is the incredible amount of carbohydrates, including refined carbohydrates, that Phelps consumes daily. In addition some members of the Australian men’s cycling team have openly boasted that they eat exclusively at McDonalds (who just happens to be a major Olympic sponsor).

    I think it highly probable that without any prompting whatsoever an enormous number of people will add 1+1 and get 11. Michael Phelps eats loads of carbohydrates + Michael Phelps is the greatest Olympic athlete in history = carbohydrates are good for you. This conclusion will be absurd because it will not even consider, among other things, the long term effects of his diet on his health. But in view of the brand power of Phelps I doubt that any amount of sound science will change people’s minds once they have decided that Phelps’s performance invalidates anything Taubes or anyone else can come up with.

    I suspect you may be right – at least in the very short run. When the next celeb comes around it will be Michael who?

  30. A little off this specific running topic, but please comment on the insulin index. The only list that I can find online is:
    http://www.mendosa.com/insulin_index.htm
    I understand that high blood sugar levels are bad, high chronic insulin levels are bad, but help me understand why beef or cheese elicits a greater insulin response than pasta, and if this is true, is their (beef, cheese) insulin response a concern? Has there been more work on the insulin index? I notice that pure fat foods aren’t on the list. Is the list an “area under the curve vs peak” argument that we’re seeing with regard to the numbers?

    I guess I need to do a post on this at some point because it’s a question I get constantly. The short answer is that insulin doesn’t operate in a vacuum. It operates in tandem with its counterregulatory hormone glucagon (also produced in the pancreas). It’s not the amounts of either that count, but the ratio of the two. Proteins stimulate an insulin response but they also stimulate a glucagon response. The ratio of the two doesn’t really change. Carbohydrate intake stimulates a large insulin response and a negative glucagon response, making the ratio skyrocket.

  31. Dr Eades: Very good article by Steve Phinney (above). This info has been available from experts such as Tim Noakes, MD for many years but Phinney recaps it concisely. Anyone interested in vigorous aerobic exercise and LC should read it. It’s a very persistent MYTH that running requires carbs.

  32. Long time lurker, big time fan of both you and Mr. Taubes. Thanks for giving me the science to defend myself against my “health care” providers and my foolish marathoning friends. Dragged in my copy of “Good Calories, Bad Calories” this morning to share with a co-worker. Can only try.

    Thanks for being out there for us non-scientists!

    I’m glad you’ve been lurking and enjoying.

    Best–

    MRE

  33. I’m curious as to what people think about this quote from the Phinney paper (http://www.nutritionandmetabolism.com/content/1/1/2):

    “Therapeutic use of ketogenic diets should not require constraint of most forms of physical labor or recreational activity, with the one caveat that anaerobic (ie, weight lifting or sprint) performance is limited by the low muscle glycogen levels induced by a ketogenic diet, and this would strongly discourage its use under most conditions of competitive athletics.”

    Is it known that muscle glycogen is systematically lower on a ketogenic diet? Or can gluconeogenesis fill up glycogen stores, given a long enough adaptation period?

    I think that people on low-carb ketogenic diets can sustain a certain amount of intense anaerobic activity, but they will ultimately outrun their ability to make enough glucose via gluconeogenesis to keep up.

  34. Dr. M:

    What is even more fascinating is that even among the low carb advocates there is not agreement. Some say lean meats(lower sat fat intake), and others say no worry to eat hi fat meats,etc. Does say something about state of nutritional science: There are no easy answers.

    Hey Steve–

    It’s important that you realize that it is the unenlightened low-carb advocates that recommend the avoidance of high-fat meats. 🙂

    Cheers–

    MRE

  35. My father held jobs that had him walk often. Ever since he was a young man, he was employed in a position where he had to stand and walk, often with heavy loads. At 60, the osteoarthritis in his right hip became so severe he could only limp to get around. The hip was unstable and he would often fall. He had no choice but a hip replacement.
    Ironically, at the time his OA was diagnosed I started having some right hip discomfort myself. I was 23 at the time. At first I thought it was psychological. Now it it’s like 2 years later and I still have it (whereas my father’s hip pain has been gone the past year, because of his hip replacement).
    I do enjoy walking frequently, I avoid public transportation or cars as much as I can get away with. I partially attribute this to my frequent walking habit. I am not able to walk as much as I would like to because it invariably triggers the pain, sometimes it gets so bad that the whole leg is in pain, even down to the knee. It seems to be getting worse, lately my lower back has been a bit stiff and sore.

    I don’t think walking is the only reason I have this problem now, at a relatively young age. I know there are other factors, but it is *certainly* true that all of my walking/standing was the trigger. The pain goes away if I am sedentary.

  36. Years of attempting to run while in ketosis told me I can’t do it. I’ve done marathons, double marathons and one 24 hour race while in ketosis. In each case I was reduced to a walk after four or five hours. My understanding of the Krebs cycle is that a small amount of glucose is needed. Hence, the “Fat burns in a carb flame” idea. In ketosis, the body catabolizes muscle protein to make the necessary sugar to feed into the Krebs cycle. These days I f0llow a low carb diet but in the days leading up to a race I fill up on carbs to reload my muscles with glycogen. I tried eating fat while running but that never worked. I tried drinking olive oil while running: big mistake. I tried eating peanut butter while running: bigger mistake. For marathon-length runs I rely on whatever carbs are available at the aid stations, usually M&Ms or cookies. For 50 milers or longer, I add some sort of protein.

  37. “We might have studies showing that men who have mistresses (and keep them well occupied) live longer than men who don’t. So therefore having a mistress leads to longevity…?”

    Well well, what do we have here?

    Want to live a little longer? Get a second wife. New research suggests that men from polygamous cultures outlive those from monogamous ones.

    After accounting for socioeconomic differences, men aged over 60 from 140 countries that practice polygamy to varying degrees lived on average 12% longer than men from 49 mostly monogamous nations, says Virpi Lummaa, an ecologist at the University of Sheffield, UK.

    http://www.newscientist.com/article/dn14564-polygamy-is-the-key-to-a-long-life.html?DCMP=ILC-hmts&nsref=news6_head_dn14564

    I love these kinds of studies. And believe them whether the data is valid or not.

  38. ME: I guess I need to do a post on this at some point because it’s a question I get constantly. The short answer is that insulin doesn’t operate in a vacuum. It operates in tandem with its counterregulatory hormone glucagon (also produced in the pancreas). It’s not the amounts of either that count, but the ratio of the two.

    I think it would be very helpful if you did a post on this with perhaps some sort of graph showing how the ratio of insulin to glucagon is affected by protein and carbohydrate. To the best of my knowledge, fat does not provoke any insulin or glucagon response which is why I eat fat if I get hungry between meals (which only seems to happen if I don’t consume enough fat with a meal).

    If you read books on the glycemic index the authors typically stress that protein should always be consumed with carbohydrate. I think it probable that they know this will favourably improve the insulin to glucagon ratio. The lack of general knowledge of the existence of an insulin/glucagon ratio has been used by some anti low carb authors to argue in favour of a high carbohydrate diet by stating that protein is worse than carbohydrate because of the amount of insulin secreted. Either these authors are abysmally ignorant or they are engaging in deception.

    The idea that protein should be consumed with carbohydrate is idiotic or. at best, demonstrates a total lack of understanding of the insulin to glucagon ratio. Both protein and carbohydrate increase insulin. Protein increases glucagon while carbohyhdrate decreases glucagon. With a mixed meal of protein and carbohydrate the insulin levels soar and the glucagon level falls, giving a greatly increased insulin to glucagon ratio, which is unfavorable to health.