Is Cardio Making you Fatter?


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cardio making you fatter

OK lets just get one thing clear…what do we need in order to put on fat? (shout it out, I know you know it).


No two ways about it, there have been no studies to date that discredit the First Law of Thermodynamics: 

“The total energy of an isolated system is constant; energy can be transformed from one form to another, but cannot be created or destroyed”

That means, if you do not have surplus energy going into your body, you can’t put on fat, because you need energy for that, and that energy cannot be magically created out of no-where.

cardio meme

How Does Cardio Make You Fatter?

Simple answer is; it doesn’t.

Not on its own anyway, because as we learnt, we need a caloric surplus to store adipose tissue. So could cardio lead to a calorie surplus? I guess it could, but that depends on a whole host of factors.

For cardio to make you fatter, you’d need to over-compensate for the energy used during the exercise. That means either your Non Exercise Activity Thermogenesis (NEAT) would have to dip considerably, or you would have to eat more total calories.

For example, lets take Mark, he usually sits on his ass all day doing an office based job, commutes to work via the tube and eats 3 pretty basic meals a day. He isn’t gaining weight, he isn’t dropping weight, he has stayed the same weight for about a year, with the same body-fat percentage. On average per week he is expending 15,400kcal or 2200kcal a day, and therefore, as per the first law of thermodynamics, we know he is consuming on average the same amount of calories 2200kcal a day.

If mark decides he wants to lose fat, or maybe just get fitter and goes for an hour run, burning 500 calories more than he normally would in the day. All things being equal he would be in a net deficit of 500 calories. If he did this everyday of the week, and didn’t change his eating or other activity he would be in a 3500 calorie deficit. Mark would most certainly lose weight, and he would definitely lose fat.

Don’t just take my word for it, countless studies have shown that cardio see’s people drop fat. In one study participants were given either a 400 calorie, a 600 calorie session or non-exercise control. They did this 5 days a week, for 10 months. If cardio makes you fatter then you would expect the two cardio groups to gain fat, and at that, the 600 calorie group to gain more. Ha! Yeah right, what really happened?

  • 400kcal group —> -2.9% loss of body-fat on average.
  • 600kcal group —> -4.4% loss of body-fat on average.
  • Control group pretty much stayed the same, as you’d expect.
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Now can people stop saying cardio makes you fatter?

The researchers concluded:

“The reductions in body weight observed in both exercise groups were a result of decreased fat mass and preservation or increase in fat-free mass.”[1]

This is just one study with countless others show the same results.

To name a few:

  • A 10-week aerobic exercise program results in a small decrease in energy intake and an associated decrease in percentage of body fat in obese adolescents.[2]
  • Twelve weeks of regular aerobic exercise led to significant reductions in body weight, body fat percentage, and body mass index in the obese.[3]
  • Aerobic exercise training can reduce % body fat and enhance vascular compliance in obese male adolescents.[4]
  • “Aerobic training is the optimal mode of exercise for reducing fat mass and body mass, while a program including resistance training is needed for increasing lean mass in middle-aged, overweight/obese individuals.”[5]
  • In obese adolescent boys, both aerobic and weight-training exercises for a 3-month period resulted in a loss of total and visceral fat.[6]

meme cardio

Look Around You!

I want you to ask yourself, who does a tonne of cardio all the time that you know that is fat? You’re probably struggling.

Now ask yourself, who does no exercise and is real fat? I bet you can answer that with many names in an instant.

Lets take that one step further, who on this planet does shedloads of cardio. Someone that springs to my mind is Mo Farah an elite long distance runner:

Mo’s Typical Training Week:

  • Monday: 16 miles
  • Tuesday: 13 miles
  • Wednesday: 17 miles
  • Thursday: 16 miles
  • Friday: 12 miles
  • Saturday: 17 miles
  • Sunday: 22-27 miles

That’s a TONNE OF CARDIO, Mo typically clocks up 125-135 miles per week. If you don’t know who Mo is, then just check out this picture.

mo farah


So not only is Mo freaking lean, which proves a bit of a point about cardio not making you fat, but you have to understand that for athletes such as Mo or even Usain Bolt carrying extra lard is like wearing a weighted backpack, it doesn’t in anyway help their performance, they have to work harder to lug the load around. Again simple science tells us that a light machine with a powerful engine travels faster.

Now you’re beginning to realise how silly the thought that cardio makes you fat is. Think, endurance running or something like the Tour De France produce a huge caloric demand on the body. Just to maintain performance these athletes must consume vast quantities of calories, and often resort to liquid meals, energy gels and the like to get them in. They literally have to force feed themselves, so they don’t lose weight!

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People often say that you become more efficient at the exercise, and therefore burn fewer calories doing it, and overtime will render it useless. But, what if the fact you were fitter, meant you could push harder, and then burn more calories? Good huh. You don’t see Mo Farah worrying about becoming efficient at burning calories.

I will note however, that although cardio doesn’t make you fatter, it could under some circumstances cause you to lose lean body mass. This has in fact been found to be the case in some studies, however, it is never all lean body mass, fat is lost too. So this cannot even be used as a case for cardio making you fatter.

Cardio Doesn’t Make You Fatter

As I said at the start, cardio don’t make you fatter, and if anyone says so, they’re just wrong. The only way you gain fat is in a caloric surplus, by doing cardio you are actively moving yourself further away from that point, thus making fat gain LESS LIKELY.

Wanna drop some fat? Enjoy cardio? Heck do it.

I’m not saying it is for everyone, for example someone looking to maintain muscle mass and strength may want to be frugal with their cardio, but cardio will not make you get fatter, and in most cases WILL HELP YOU LOSE FAT. But remember, that is only so long as you don’t decide to pig out, ridding that calorie deficit.

  1. Lee, S.S., et al., The Effects of 12 Weeks Regular Aerobic Exercise on Brain-derived Neurotrophic Factor and Inflammatory Factors in Juvenile Obesity and Type 2 Diabetes Mellitus. J Phys Ther Sci, 2014.26(8): p. 1199-204.
  2. Song, J.K., et al., Effects of 12 weeks of aerobic exercise on body composition and vascular compliance in obese boys. J Sports Med Phys Fitness, 2012. 52(5): p. 522-9.
  3. Willis, L.H., et al., Effects of aerobic and/or resistance training on body mass and fat mass in overweight or obese adults. J Appl Physiol (1985), 2012. 113(12): p. 1831-7.
  4. Lee, S., et al., Effects of aerobic versus resistance exercise without caloric restriction on abdominal fat, intrahepatic lipid, and insulin sensitivity in obese adolescent boys: a randomized, controlled trial. Diabetes, 2012. 61(11): p. 2787-95.


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