Correlation vs. Causation

Today’s article counts as more of a rant than anything, but I feel that this needs to be said lest I crack my forehead open from banging my head against the wall too many times. I’ve noticed a very common trend in the fitness community and beyond. I’ll keep this one relatively short for ease of read; I have a feeling I’ll find myself referring many individuals back to this piece.

Before you go on and make any kind of claim that you did x and therefore y happened, I urge you to please, please consider the difference between correlation and causation.

It’s very easy to fall into this trap. You change some behavior or adopt a new habit, and all of a sudden, you attribute that new thing as the cause of your success or failure.

But let’s rewind back to that high school science class for a few minutes here. Yeah, remember those times? It’s time to swat away those cobwebs in your brain and brush up on one of the basic foundations of none other than the scientific method.


To better illustrate today’s message, let me use a few examples:

  1. I dropped 20lbs of fat by eating six meals a day consisting of clean foods – no cheese, definitely no dairy, certainly never any of that God-forbidden fruit.


  1. I lost weight because I ran a half marathon every day, therefore cardio is an effective way to shed fat.

The above two statements are those of correlation, not causation. Please, let’s not confuse the two.

The process of going about establishing a causal relationship between two variables (in this case, changed dietary habit/ exercise and fat loss) is much more complicated than determining a correlational relationship. With the former, you must control every single condition except for that which you want to test – and in everyday life, doing so is often unrealistic and not feasible. With the latter, all you have to do is show that as x variable changes, y variable tends to change in a certain way.

Want to prove that small, frequent meals are the magic secret to an enviable physique? Okay, fine. But first, make sure that every other possible factor remains the same. Don’t change the total number of calories consumed; don’t even change the types of foods eaten. Don’t alter physical activity levels, amount of sleep, level of stress, or even coffee consumption. We don’t want any kind of selection bias when choosing your sample population, and oh yeah – make sure your sample size is large enough.

How about this well-known example: The rooster crows every morning before the sun comes up, therefore the rooster is what causes the sun to rise. How ludicrous does such a claim seem to you? Yet this is what so many of us do in the realm of fitness without even realizing it. Sure, there is a temporal relationship between the crow and the rising of the sun, but… even if the rooster doesn’t crow, I assure you the sun will still come out tomorrow. (Annie told me so.)

Reasons for the Confusion

There are many reasons to confuse correlation with causation. Below are the most common ones.

Confounding factor. See rooster example above. Yes, you lost fat, but not due to your frequent feedings. Rather, there was a third variable that you forgot to take into account: decreased calorie consumption. You not only took many of the calorie-dense foods out of your diet, but in doing so, you ended up ingesting fewer calories than you previously did, hence the weight loss. And don’t tell me when you started running all those miles you also didn’t start watching your diet at the same time.

Confirmation bias. Often when you go about investigating a question with a specific answer already in mind, you skew and misinterpret the results so you actually get what you want. Cherry-picking? Yeah, don’t do that. Any decently educated individual will immediately call you out on your bullshit and make you look like a… not-so-decently educated individual, to put it nicely.

Mere coincidence. I don’t think this one requires further elaboration.

So Before You Make a Claim….

Do yourself a favor and think twice as to whether the Shakeweight actually works or if it’s everything else you’re doing – such as eating right and training properly and getting enough sleep. Maybe, just maybe… it might be the latter. And maybe, just maybe… you’re successful in spite of some idiotic behavior you’re practicing (such as That-Which-Shall-Not-Be-Named, aka superfluous implementation of cardiovascular bodily hustle and bustle).


And this concludes my rant. You may now resume your lives.

Oh yeah, and don’t forget to eat your protein and lift heavy sh!t. Have a good day. :)

About the author  ⁄ soheelee

I am a fitness buff with a Stanford B.A. in Human Biology – Psychosocial and Biological Determinants of Health. I’m also an NSCA-certified personal trainer and a nationally qualified NPC bikini competitor. I've written on, Greatist, and other awesome publications sharing tips on fitness, psychology, and motivation.

  • Ann (@TheWellnessChick)

    Oh hay this article is awesome.

    I cannot tell you how many times people have claimed that they lost weight with clean eating. Of course, once you closely look at their eating habits, you see they’re eating fewer calories than they did with their normal diet. But oh no, it’s the magic of fruit, vegetables, and grass-fed beef that is shedding the fat.


  • Kate

    Could not love an article more!! I “liked” a certain fitness magazine on FB a few months ago… every so often they post short “facts” newly found through science and present them as such, even though they are merely correlations.. and when stated as facts sound absurd. I can’t believe the kind of shit that that people buy into.

  • Patricia

    Fan-freakin-tastic article, Sohee. :)

  • jeremy

    Great article…

    Another brilliant (and real) causation / correlation example is Why would you wear a helmet to war?

    When metal helmets were introduced to troops in the First World War, the reported head injury rate increased significantly. Far more soldiers presented with head injuries.

    In the absence of all other data, this would indicate that wearing a tin helmet in a war means you’re more likely to get a head injury. Right? More injuries = an ineffective solution. So…why would you wear a helmet to a war?

    ….because the head fatality rate (how many people die because they got shot in the head) dropped by more than the head injury rate increased. Helmets were turning dead soldiers into injured soldiers.

  • Brian

    Awesome article. I get very annoyed myself whenever I see this in the news, or hear about it through friends. Its not just endemic to the fitness community, it pops up almost everywhere.

  • Ned

    I think this is a great reminder to look at all facets of a situation before deciding that it’s one thing or another. However, the insistence that cardiovascular work is superfluous just doesn’t wash. Here you need to remind yourself of what you’ve just written. If you start running and burning more calories for a certain period of time, but don’t increase your intake, you will lose weight. You’ll burn off fat. I’ve done it, and my wife has done it, with no added resistance training, when we’ve kept our diet steady. It hasn’t worked when we’ve given in to the increased appetite and eaten more. I agree with the idea that resistance training and added muscle cranks up the metabolism more than most people think, and should be part of a good fitness regimen, but to suggest that cardio is superfluous is off base at best.

    • Sohee Lee

      Ned – Just about everything “works” for about 6 weeks. I’m sticking to my guns here: cardio is superfluous for the most part. But thanks.

      • Ned

        Indeed it does. It even works for longer than six weeks. You just have to monitor it, work it, tweek it here and there. You need to work through the plateaus, as you do with lifting. You need to adjust for progress. Like anything else you do long term, you need to manage it.

        • Sohee Lee

          How would you adjust your progress? Increase the cardio?

    • Zoharian

      Please keep in mind she isn’t saying it doesn’t work but that it is superfluous. And your evidence shows causation at best. Know what else will help you lose weight? Stop eating. There are millions of proven cases that if you stop consuming any calories you will lose weight, no matter what shape you are currently in! But that would be superfluous wouldn’t it?

    • http://DYEL DYEL

      Ned, do you even lift?

      • Ned

        I do lift a bit. Not a lot. I do a lot of bodyweight things instead, pull ups, pushups, etc…. I find being inside a weight room bears down on me after a while. I use leg machines since I have a severed ACL and reduced meniscus in one knee from decades ago that was never repaired (they didn’t have it down yet in the late Seventies). I swim, and I walk run stadium benches.

        I found that my weight dropped when I did a lot of riding, walking, swimming, and what have you cardiovascularly, and didn’t increase my eating. There was no extra resistance training involved. Wasn’t that into it then.

  • Ned

    Right, causation. Cardio of various kinds helps us keep our weight steady or dropping. When we stop or take a break and the diet stays the same, the weight climbs. Calories in and out. How is that superfluous, rather than just a different method?

    • Sohee Lee

      Ned, I think you’re missing the mark here. If you’re running 15 miles a day, that’s one thing. That’s when you have to ask yourself if what you’re doing is really all that effective – which was my initial point.

      I also cited this study (Thorogood A, et al. Isolated aerobic exercise and weight loss: a systematic review and meta-analysis of randomized controlled trials. Am J Med. 2011 Aug;124(8):747-55) in a previous article, and Alwyn has this to say:

      “14 studies on weight loss and aerobic exercise with 1847 participants have failed to show any meaningful results. Isn’t it time we faced the truth that it [cardio] just isn’t a fat loss tool?”

      I have to disagree that when you stop cardio, weight climbs. In fact, I’ve witnessed the very opposite with several friends and clients. While anecdotal evidence isn’t sufficient to prove a point, I think it goes a long way to suggest that the effectiveness of cardio is grossly overexaggerated.

      • Ned

        My weight climbed when I stopped burning calories at the rate I was burning them. I wasn’t running 15 miles a day. I was walking about 3 or 4, swimming about a mile a day, and using the stairs as often as I could. When I had to cut back for various reasons, my weight climbed.

  • Jonathan Goodman

    I actually agree with Ned on this one. Cardio is a tried and tested method for losing weight. It may not be the most efficient but it sure as hell works (even beyond 6 weeks).

    Most from the “hating on cardio” camp also don’t take into account just how difficult HIIT and circuit training is. With most of the overworked and overstressed population the thought of having to push heavy weights and move really fast is enough to keep them out of the gym. Going for a run that isn’t too difficult is a great way to deload after a stressful day. Sure it may take a little longer.

    I just think the cardio is evil mantra has gone too far. I don’t do cardio but I understand it’s the best option for most of my clients.

    I’m also worried that this thought-process is going to confuse people into feeling awkward working out in the gym which is exactly the opposite point we’re trying to make

    • John

      “With most of the overworked and overstressed population the thought of having to push heavy weights and move really fast is enough to keep them out of the gym.”

      …and that’s why they’re still fat.

  • Chris

    Yes, aerobic exercise alone will not lead to weight loss (in the obese). However, neither will lifting heavy shit. Both must be accompanied by an adjustment in one’s diet.

    Beyond that, it’s just a matter of what one prefers and what one’s goals are.

    • Sohee Lee

      That is correct – nowhere did I imply as such. My point was that there are too many people who say things like, “I heard cardio is the best way to drop fat. I’m gonna go do a ton of it.” (I dare you to tell me you’ve never heard anyone say that.) Yet I think it’s more common knowledge that people won’t magically get leaner just from lifting weights.

  • A.J.

    I don’t do cardio solely to lose weight. I use it as a supplement to my workout routine (which varies but typically includes weights) and diet (which sucks, but I do the best I can). It warms me up when I’m cold (heyho, metabolism), and makes me more prepared for “weekend warrior” activities because my heart is stronger. People need to stop dismissing cardio and simply make clear its contribution to the healthy lifestyle. No cardio can’t be better than some cardio.

    • Sohee Lee

      A.J., you may be surprised to learn that I’m 100% on board with you with this. I never said anywhere that cardio is evil or that it should be avoided at all costs. That’s neither here nor there, however, as that’s actually not the point of this article.

      • A.J.

        I kind of had the feeling, but still felt it ought to be said. Please do keep writing, you have a refreshing style. :)