The Math Behind Why Cardio Won’t Help You Lose Weight
And what to do instead.
Whether it is a New Year resolution, damage control after gaining a few pounds over the holidays, or preparing urgently for a class reunion, doing tons of cardio sessions has always been a favorite choice for those looking to lose weight quickly.
Whether this choice is so popular because the weightlifting section at the gym looks intimidating, because of magazine articles on “How to lose weight fast” advertising spin classes, or because movies have perpetuated the romanticism of running up and down stairs…One thing is certain: That approach does not work.
Doing tons of cardio will not help you get back in shape, and, to prove it, I’ve got some math for you. (Don’t run away now, I’m telling you, that won’t help!)
Let’s do some basic math
There is no denying that cardiovascular activities are great for your overall health and will also increase your endurance. But, when it comes to losing weight, your “return on investment” isn’t that great. It’s not really a strategy to lose weight, but a losing strategy instead.
Take for instance the following screenshot of my Garmin cycling activity from Feb 2020 until 05 Jan 2021.
As you can see, I’ve been extremely consistent, cycling almost every day for an hour on my Tacx turbo trainer. The data is recorded automatically and sync’ed. (Note: I cycle on top of weightlifting and running, for general health and fitness.)
Based on my average speed range (19–22 km/hr), I estimate that to cycle these 6,237.4 km, it has taken me between 284 and 328 hours. So let’s take the average of that and say it took me 306 hours for simplicity.
Further, based on my stats, Garmin estimates I have burned 60,153 calories during these 306 hours. While there are debates about the accuracy of sports watches,¹ this comes down to around 197 calories/hour — a very reasonable-sounding number for this sort of activity, especially compared to online calculators which will often suggest over twice as much.
Assuming that the numbers are sufficiently accurate for napkin math, let’s see how much weight you could supposedly lose after 306 hours of cycling:
- It is generally agreed that 1 pound = 3,500 calories.²
- 60,153/3,500 = 17.19 pounds (or 7.8 kilograms).
Now, I don’t know about you, but that doesn’t seem like much for the amount of work and time! Besides, if we were in a rush, looking to lose weight “quickly”, we’d have to cycle 3 hours/day, and it would still take us 102 days or over three months!
Unless you are a hardcore cyclist who can spend that much time each day (or who can cycle much more intensely to cut down on the hours a bit — in which case you probably already are in great shape!), that is a lot of freaking hours. Probably doable for an actor who is urgently preparing for an important role, but not very realistic for most people, especially if you also have a busy job or family, or if partake in other activities as well, or have other time-demanding obligations.
What about if…
What about if you chose an activity that burns more calories per hour, such as running, so that you lose more weight? As someone who has run ten half-marathons and three marathons, I can tell you that if that made it any better, everyone on race day would be shredded because long-distance runners spend a lot of time running. But many runners are far from being shredded because even if you are willing to spend 306 hours running, you can very easily erase any deficit by compensating with a higher calorie intake without realizing it. That is, assuming you are even actually capable of running so much as such activities have not only higher intensity, but also have greater impact. They take a toll on the body and require more recovery, particularly if you have not been regularly performing them before.
To make matters worse…
To make matters worse, the above calculations are giving us a best-case scenario of what you could lose in theory if all other variables remain the same. However, in reality, other variables will inevitably change as well, and not in your favor:
- Calories burned during cardio (a.k.a. exercise-related activity thermogenesis or EAT) will decrease. The more youperform an activity, the more the body adapts and becomes efficient at it. The more efficient it is, the fewer calories it burns.³
- Weight loss will decrease your resting metabolic rate (a.k.a. RMR). The lighter you are, the fewer calories you need.⁴
- Weight loss will usually include some lean mass loss, which will lead to an even greater reduction in daily calorie expenditure. This could get really bad if a lot of muscle is lost, for instance, due to a combination of too much cardio, not enough protein, and no resistance training.⁵
- You could unconsciously decrease your general daily activity levels (a.k.a. non-exercise activity thermogenesis or NEAT) if you are feeling tired from doing too much cardio and thus could decrease the calories you burn from simply moving around less. Your old couch always looks more attractive after a long running session — trust me on that one.
A working alternative
You can’t really argue with math: While cardio might have many health benefits, doing tons of it is not an efficient way to lose weight, and any of its efficacy will also progressively diminish. Even if you have the discipline to be consistent, it demands many hours, requires recovery periods proportional to the intensity of the exercise, and its potency decreases over time. Fortunately, if you do have discipline, there’s an excellent alternative that requires nothing further than just that discipline.
That alternative is… Watching what you eat.
It might not sound particularly exciting, but, thanks to many available mobile apps, it is nowadays easy and fast to track your calorie intake. All you need to do is to calculate your caloric needs using an online calculator (if you are reading this article, likely an easy task for you!) and then decide on a daily deficit to achieve the weight loss you’d like.
For example, if you’d like to lose 15 pounds over 12 weeks:
- 15/12 = average loss of 1.25 pound per week;
- 1.25 * 3,500 = an average weekly deficit of 4,375 calories;
- 4,375/7 = an average daily deficit of 625 calories.
Finally, subtract these 625 calories from your daily caloric needs. (Note: You will occasionally need to adjust the latter as you lose weight since, as discussed, your RMR will decrease as you become lighter). The result from that subtraction will be your daily caloric intake goal.
This method is foolproof if you track accurately and honestly. (Every single little bite counts, including when you lick clean the peanut butter spoon!) Moreover, you’ll be able to adjust as needed depending on the speed with which you lose weight. If it’s too fast, you could bump up your food. If it’s too slow, you could either decrease your calories a little further or, here, use cardio strategically to boost your deficit through moderate increases in energy expenditure.
You can think of this method as budgeting. Just like you budget your income in order to pay your bills or save for a vacation and every dollar counts, you budget your calories. It may be a bit boring, but it is the responsible approach. Moreover, it is the approach that works and that will not lead you to any bad surprises at the end of the month.
Tracking your food has the additional benefit that it’ll show your macro distribution as well (protein, carbs, and fat) if you want to get real “fancy” with your diet later on. The caloric deficit will ultimately drive the number on your scale down, but what you eat and your macros will impact your energy levels as well as body composition (lean mass vs. fat) and therefore, your looks, regardless of what the scale shows.
[1] Roos, Lilian et al. “Validity of sports watches when estimating energy expenditure during running.” BMC sports science, medicine & rehabilitation vol. 9 22. 20 Dec. 2017, doi:10.1186/s13102–017–0089–6
[2] MayoClinic. https://www.mayoclinic.org/healthy-lifestyle/weight-loss/in-depth/calories/art-20048065
[3] Wilson, Claire. “Our body adapts to intense exercise to burn fewer calories.” NewScientist, 1 Feb. 2016, https://www.newscientist.com/article/2075721-our-body-adapts-to-intense-exercise-to-burn-fewer-calories/
[4] Chung, Nana et al. “Non-exercise activity thermogenesis (NEAT): a component of total daily energy expenditure.” Journal of exercise nutrition & biochemistry vol. 22,2 (2018): 23–30. doi:10.20463/jenb.2018.0013.
[5] Davis, Jeanie Lerche Davis. “Get More Burn From Your Workout.” WebMD. https://www.webmd.com/fitness-exercise/features/get-more-burn-from-your-workout
You just read another post from In Fitness And In Health: a health and fitness community dedicated to sharing knowledge, lessons, and suggestions to living happier, healthier lives.
If you’d like to join our newsletter and receive more stories like this one, tap here.
