The Cardio Trap: Can too much cardio block fat burn?

Can too much cardio actually cause your body to hold on to fat, rather than burn it? And if so, how much is too much?  Today we’re looking at heavy cardio to determine if there’s a connection between “too much” and “can’t lose weight”.

From an evolutionary standpoint, there are several universal truths that are important to recognize in order to have a successful fitness and weight loss journey.  First, which we’ve talked about many times in the past, our bodies are hard-wired to require high levels of protein in order to burn fat. Second, if you eat more calories than your body requires, you’ll gain weight (and if you eat fewer, you’ll lose weight). And third, exercise (all exercise) burns calories.

Blame Evolution

Speaking purely from an evolutionary standpoint, our bodies are also hard-wired with a “fight or flight” mechanism designed to preserve fat when our “comfort zone” is threatened.  The bodies of our ancient ancestors were (quite literally) programmed to preserve fat at all costs when faced with difficult or stressful situations that were outside of their norm. “Holding on to fat” became the ultimate insurance policy that our bodies had against long periods of “unknown”.

As in, “Something is wrong. We are stressed. We aren’t getting enough food. Our workload is increasing. We need to preserve our energy stores!”  [Or, put another way, block fat burn — because we might need it!!]

Finding the balance

Weight loss is, effectively, a delicate balance between not placing your body into a state of stress, and not eating so much food that you can’t shed the pounds. There’s a pretty big window of opportunity there, but it certainly doesn’t help that your body will generally adapt over time to whatever you throw at it. Hence the reason breaking a plateau is all about changing things up — and not necessarily about just “eating less” or “exercising more”.

Generally speaking, weight loss is accelerated when we do moderate and healthy amounts of exercise every week. More specifically, anywhere from 30 to 60 minutes a day is actually ideal (with one or two rest-days per week). Your heart-rate should be up. You should be sweating profusely. You should be breathing hard. And most importantly, when the workout is over, you should be TIRED!! All of this will place you in the “just right” zone for fat burn.

The Cardio Trap

Some people, however, get caught in the “Cardio Trap”, believing that if they continue to increase their cardio workload, the scale will start moving again (as in, they’re trying to break a plateau), or the scale will move faster.  They increase their cardio to 90+ minutes a day, or even higher — only to find that, while it works for a little while, perhaps a few weeks, the scale suddenly stops moving altogether — no matter how much exercise they do, or how little food they eat.

First, it’s important to note that increase your cardio beyond 60 minutes a day, or decreasing calories, are really not the most effective methods for breaking a plateau.  It’s also not a great idea to target your weight loss at more than 2lbs per week (Some people try to get the scale to move faster than that by exercising more).

The two most common mistakes you can make in your weight loss journey, both of which lead to the production of a hormone know as “cortisol”, are: (1) Eating too few calories (less than 1,200 is a guaranteed recipe for destroying your metabolism), and (2) doing more than about 60 minutes of cardio per day, on average.

Cortisol is known as the stress hormone. It’s produced when your body is stressed, and it has several interesting side-effects when it’s floating around in your system.

  1. Your body will fiercely resist all fat burn. And in fact, may go into a “storage” mode where most of the food you feed it gets stored as fat. (In other words, you may even GAIN weight in extreme circumstances).
  2. Your body is much MORE likely to burn muscle, instead of fat (so even if the scale is moving under heavy cortisol production, it’s usually the result of muscle-mass burn rather than fat-burn).
  3. You’ll probably be tired a lot. The calories-in / calories-out rule still applies, so your body simply slows your metabolism to compensate. This is called “Adaptive Thermogenesis”.

Not coincidentally, this is why most serious endurance runners are not only extremely skinny (very little muscle on their bodies), but they are also likely to GAIN weight during heavy training periods, AND they find that if they slow down their training schedule, they get fat very quickly. (Their metabolism had adjusted to the heavy running, and they have no muscle to fuel it, so when they stop running for even a short period of time, the pounds pack on!)

The Vicious Cycle

For those trying to lose weight through increased cardio, the cycle can be vicious and usually looks something like this:


So is cardio bad?

To be clear, I am by no means suggesting that cardio is bad, or that cardio is going to set you back in your weight loss journey.  Quite frankly, less than 1% of the people I’ve ever talked to or worked with fall into a category where too much cardio becomes a problem. You should be exercising, whether you do strength or cardio is up to you (although one is definitely better than the other). The key is to keep it in moderation. No more than 60 minutes a day of heavy cardio!!

If you have the time to dedicate to 90+ minutes of exercise, however, you may find the magic formula is a combination of cardio and strength training (weights).  Do half your cardio at the beginning, then do weight training, then finish your cardio session. (As an example, you might do 25 minutes of cardio followed by 40 minutes of weight training, followed by another 25 minutes of cardio). This combination increases your metabolism, fuels fat burn (since your body will be starving for fuel by the time you start your second round of cardio), and it increases the production of HGH (Human Growth Hormone) which is fuel on the fat-burn fire!

If you DO end up doing more than 60-90 minutes of cardio in a single day, one of the ways you can help offset cortisol production (and convince your body that it’s not going to starve to death) is to increase calories for that day. Normally we avoid eating our workouts calories (since the goal is weight loss), but offsetting cortisol is definitely more important, since we don’t want to block fat burn altogether. As an example, if you do 1,000 calories worth of cardio, I would eat back at LEAST half of that number, if not more, to keep your body in a state of comfort.