Could Cardio Be Making You Fat?

Could Cardio Be Making You Fat?

There seems to be still a large misunderstanding by experienced gym goers and even some personal trainers on the effect that cardio has on losing fat and trying to attain a lean defined physique.


On the one hand you may have heard that “cardio will make you fat!” and simply just being in the same proximity as a treadmill or going for a jog will cause uncontrollable fat gain.


On the other hand you have those who promote that the more the better, and that you simply need to burn more calories than you consume, as it’s a basic equation of energy in vs. energy out so go nuts and rack up as many hours as you can.


By this point I hope you already understand that neither of these statement are true and that use of cardio as a tool for improving your physique depends on many underlying factors.


The term cardio is used quite loosely, but for the sake of this article we are referring to activities that utilize primarily the cardiovascular system so think: running, swimming, cycling or any other moderate-intensity steady state aerobic work.


Some trainers may state:  “Cardio will make you fat!”


This is not true.


Cardio will not directly cause you to gain fat. You will gain fat when the energy (calories or kilojoules) entering the body exceeds those that are burned for energy or that leave the body.


However this is not a simple equation of energy in vs. energy out, as it doesn’t account for

- Macronutrient ratios

- Nutrient deficiencies

- Insulin response

- How the body alters hormone levels that dictate hunger and the use of fat for fuel.

- Chemical exposure from food additives, pesticides and other known toxic substances that work as hormone disruptors negatively influencing body fat levels and health


So although cardio doesn’t directly make you fat, there are certain situations in which doing cardio along with other popular misunderstood behaviors of trying to lose weight will result in fat gain.


The use of cardio training as primary fat loss tool stems from the false misconception that exercise should focus on burning calories rather than building lean muscle tissue. This idea is supported by conventional wisdom that promotes endurance training as the best way to get healthy or stay fit.


What people generally don’t understand is that all cardio is good for is improving how long you can run, swim or ride for. This is great if you are an endurance athlete but not if you are aiming to improve your physique.


The primary reasons behind why too much cardio can make you fat are:


  1. Chronic Elevation of Cortisol
  1. Break Down of Muscle Tissue and inhibition on building muscle
  1. Decrease in resting metabolic rate


  1. Too much cardio = Excess cortisol


Those who are chronically stressed out from their lifestyle or chronically stressed out from doing too much endurance style training are more likely to gain fat from doing cardio, as cortisol will remain excessively elevated.


A study completed by Skolund N, et al. in 2011 found that cortisol levels where elevated by an average of 42% above controls in 304 amateur level endurance athletes.


This elevation of cortisol from excessive training will greatly decrease the body’s ability to burn fat and build muscle as excessive cortisol causes:

- Cells to become resistant to insulin, causing inflammation and making fat burning extremely difficult = you cant access your fat stores to burn them

- High cortisol will cause you to crave sugar

- High cortisol suppresses other key hormones like testosterone and growth hormone leading to belly fat gain

- Hormones that control hunger can become imbalanced which generally result in overeating and constant hunger.

- Other negative consequences of excessive cortisol include altered immune function, cognitive decline, damaged reproductive health, bone loss, advanced ageing.


Along with the long list above of the negative consequences above, excessive cortisol causes a low T:C (testosterone: cortisol) ratio which results in the breakdown of your hard earned muscle tissue which leads us to our next point.


  1. Cardio causes the breakdown of your hard earned muscle tissue and inhibits new muscle growth.


Scientist believe that aerobic style cardio training switches off muscle building pathways, promoting catabolism and inhibiting muscle growth.


This was demonstrated by Lo, M., et al. where researchers had a group of elite cyclists commit to a strength-training program. Group one completed a strength training program and did no cycling while Group two completed the same strength program but continued with their regular cycling training.


Results showed that group one increased their lean body mass by 1kg where group two that continued cycling in conjunction with weight training gained zero.


This demonstrates that cardio inhibits muscle building, which is very significant as we want to be able to build as much muscle as we can to help increase our metabolic rate allowing us to eat more without gaining any fat.


The main reasoning behind why cardio reduces the ability to build and maintain muscle is that it produces a negative hormonal response. When cardio bouts last longer than 20-30 minutes cortisol levels continue to rise while testosterone levels decrease resulting in a low T:C ratio which leaves you in a catabolic muscle-wasting environment. When this is done repeatedly session after session, week after week this will eventually lead to a reduced resting metabolic rate (RMR) which is bad news if your goal is attaining a head turning physique.


  1. Too much Cardio = Reduced Resting Metabolic Rate (RMR)


If you are female, you may be thinking ‘so what’ and may not be worried about building muscle tissue, losing muscle mass or having a high RMR. But unfortunately this is why so many females struggle with being ‘skinny fat’. They look skinny through clothing due to a lack of muscle mass but they are actually fatter and unhealthier than they think.


The main reason why so many put themselves through long bouts of mind numbing cardio is because they’ve been led to believe that they want to lose ‘weight’ and that the best way to do this is to consume less calories while trying to burn off as much as possible.


Although this method may work short term, and the number on the bathroom scales may decrease, the results are short-lived and the damage done to the metabolism can be long lasting.


The human body is a very efficient machine, so as you decrease your energy intake (lower calories) and increase your energy expenditure (excessive cardio), your body will begin to store body fat for future needs, while decreasing your RMR, burning off energy using tissues (muscle) while at the same time increasing your hunger.


So as soon as you come off your ‘diet’ you quickly gain the weight you lost (which was 50% muscle) back in fat, and you are left with a fatter version of yourself who weighs about the same or even more. Sounds like fun, right?


So what is the solution?




Trainees who focus on building muscle always look better than those focusing on burning calories.


Our RMR is responsible for 60-75% of our total energy expenditure so people, who require more energy at rest, need less exercise to maintain a lean physique. So instead of being hungry, with your body storing fat and losing muscle, you become a fat burning machine and you will begin to gain muscle as you are in an anabolic environment.


Instead of steady state cardio focus your efforts on training with weights. For optimal results start with 4 weight training sessions per week using large compound movements like squats, deadlifts, press’s, rows and pull-ups.


For extra fat burning do High Intensity Interval Training (HIIT) like sprints or modified strongman style training. A great way to increase your fat burning response it to add in 5-10 minutes of HIIT style training as a finisher at the end of your training session.


In summary:


  • Excessive cardio training can actually be making you fatter when done incorrectly long term.
  • This is caused by:
  1. Excessive cortisol production
  2. Breakdown of hard earned muscle tissue and inhibition of building new muscle
  3. Reduced Resting Metabolic rate


  • Instead train to build, not burn by training with weights four times per week and adding in HIIT training separately or after weight sessions.


Train smart.

Tyler Cosnett.


Lo, M., Et al. Training and Detraining Effects of the Resistance Vs. Endurance Program on Body Composition, Body Size and Physical Performance in Young Men. Journal of Strength and Conditioning Research. 2011. 25(8), 2246-2254.


Skoluda, N., Et al. Elevated Hair Cortisol Concentrations in Endurance Athletes. Psychoneuroendocrinology. 2012 37(5): 611-7.

Leave a comment!

You must be logged in to post a comment.