Is Chronic Cardio Making You Fat? (It May Be!)


This week an old news article has resurfaced claiming that doing cardio makes you fat. Some of my favorite quotes from the article (which doesn't actually link to any of the research they talk about):

  • If you want to gain weight, you should get on the treadmill or go out for a nice slow jog.
  • Several new studies show that long and boring cardio workouts actually sabotage your body’s natural ability to burn ugly belly fat.
  • When you spend 30, 40 or even 60 minutes pounding away on a treadmill, you send your body a powerful signal to start storing fat instead of burning it.
  • If that weren’t enough…cardio increases your appetite. This is a physical as well as an emotional response. Your body craves it, and you believe you earned it…which isn’t true. In fact, most folks end up eating an average of 100 calories more than they just burned off.
  • Perhaps worst of all, after 20 to 30 minutes, most classic, steady-state cardiovascular exercise begins to chew up your precious, calorie-burning muscle.

So - scared enough to swear off doing cardio ever again? Let's take a closer look at this ...

Chronic CardioThe study the article was referencing was from the European Journal of Applied Physiology in 2003. Their research looked at 21 participants and concluded that people who engaged in chronic cardio produced less T3 hormone. When this hormone is suppressed your body starts to store more fat. SO MANY PROBLEMS WITH THIS RESEARCH! First, their sample size was ridiculously small. Also, they didn't even measure body fat gained at the end of the study. So just because T3 levels were lowered, which correlates to fat storage, doesn't mean the 17 college aged athletes actually gained any fat or weight.

Still, I did some digging and found some compelling arguments against doing chronic cardio (think running for 45-60+ minutes at a time.)

One of my favorite blogs to read is Mark's Daily Apple. Mark is the author of the Primal Blueprint book and while I don't follow a primal lifestyle I love his no-nonsense, research based approach to health and fitness. He preaches a lot against chronic cardio (read his article for explanations behind all of it.) Here are a few of the issues he has with it:

  • Endurance athletes are at greater risk for atrial fibrillations (irregular heartbeats.) Moderate exercisers have a lower risk of this.
  • Marathoners are more likely to have calcified plaque in their coronary arteries than non-marathoners. This leads to stroke and dementia.
  • Constant breaking down of our systems to become faster, and run farther, leads to oxidative stress.
  • He ends with some anecdotal observations he's noticed in his endurance athlete friends; bad backs,  osteoarthritis, hip and knee replacements, and chronic tendonitis. 

Is he absolutely against half or full marathon training? No! (Another reason why I love him.)

I’m even OK with running marathons occasionally or jumping into a short triathlon now and then. As a species, we obviously have the capacity to go long and relatively hard every now and again. It’s the chronic, day-in, day-out long, hard stuff that is counter-productive. If you did that twenty thousand years ago, when your next meal – and that of your entire family/tribe – was on the line, when calories were somewhat precious, when you didn’t have an air-conditioned caravan of trainers, massage therapists, and coolers filled with electrolyte drinks following along after you, you’d be foolish. You simply wouldn’t do it. (Check out his advice for training for a marathon.)

Finally, a few more anti-cardio bits of information from this article.

  • Aerobic-style cardio is most effective if you are overweight and new to exercise
  • Eventually, the body adapts and uses energy and oxygen more efficiently during cardio, making it less effective for fat loss.
  • Too much cardio can lead to increased hunger and food intake, which leads to fat gain.People with elevated cortisol from chronic stress are less likely to lose body fat from cardio because high cortisol causes the body to store fat.
  • Cardio interferes with muscle building.
  • Interval training is more likely to produce fat loss than cardio (do HIIT and speed work), and it will allow you to save training time because it builds lean muscle mass.

From my own person experience I would agree 100% with the point above. Before I started marathon training I weighed 112 pounds, was at about 17% body fat, and ate about 1600 calories a day. I worked out at home doing barre/strength workouts 5x a week.

After I started running consistently, averaging maybe 30-40 miles a week, I weighed 120 pounds, was at about 21-22% body fat, and ate about 2000 calories a day. I was strength training at home maybe 2x a week.

When the miles started adding up, I was simply too tired and too busy to keep strength training. I don't care too much what a scale tells me, but my body went from being pretty toned and muscular to .... soft. Yeah I could run 20 miles at a time but I didn't feel strong anymore. My posture wasn't as good as it was when I was actively working out my core and back, and I was burning less calories at rest due to decreased muscle mass. I also went from eating tons of veggie based meals to ALL THE CARBS.

Will I stop distance running? Hell no! It's a great emotional release for me. However, I have been much more consistent with strength training, and I haven't run anything over 13.1 miles in 4 months (and don't plan to anytime soon but there is an ultramarathon somewhere in my future!)

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How much cardio do you do each week?  Do you think there is such a thing as too much?