Can You Do Too Much Cardio

Posted by FiscusFitness, LLC on September 9, 2016

If you want to lose weight, you need to burn calories.  You can restrict the amount of food you eat, increase the amount of calories you burn through exercise or try to tackle both. In an attempt to achieve as much fat loss as possible in the shortest amount of time there are people out there who will drastically cut calories while adding hours of cardio.  But, tacking on extra cardiovascular exercise may not be the best answer in terms of fat loss.

Cardiovascular exercise or aerobic exercise includes acitvities such as walking, running or biking.  It temporarily increases your heart rate and respiration, while building your endurance. It's different than anaerobic activities such as weightlifting and sprinting which tend to build muscle and physical strength through short bursts of strenuous activity. Throughout this article, I'm strictly talking about too much cardio, not too much weight training (which is a whole other subject).

Cardiovascular Adaptations

When you first start working out, you might burn 300 calories walking three miles an hour for 60 minutes.  But, as you get more fit… the walking becomes easier. Your body adapts to the stress on it, so you burn less calories doing the same thing.  In addition, if you have dropped any weight in that time period, your overall resting metabolic rate is lower to account for your smaller size. You may be burning 250 calories doing the same walk.  People don’t realize how quickly this adaptation can occur.

So what harm is 50 little calories?

Assuming you are eating at maintenance, that slight miscalculation can lead to a 350 calorie excess per week.  That’s a tenth of a pound a week or a little more than a five pound weight gain a year.  And that’s just 50 calories! 

Combining Cardio with Caloric Restriction

When this adaption occurs, dieters try to outsmart the body and turn to more cardiovascular exercise and more caloric restriction.  That is where the trouble comes in.  The body is designed to protect itself from a huge deficit.  You are meant to have fat stores.  So, when you try to fight your body’s natural design.. it fights back.

The Cortisol/Leptin Connection

Cortisol is released into the body in response to stress.  It is not an exclusively bad or good hormone, but has gotten a bad reputation in terms of fat loss.  Exercise is a stress. Dieting is a stress.  When you combine the two together your cortisol shoots up.  Cortisol causes an increase of water retention, to the point where it doesn’t look like you are losing weight anymore. At the very least, it looks like you are at a plateau even while doing massive amounts of exercise in a deficit. 

It is also thought a long term elevation in cortisol level causes leptin resistance.  Leptin was discovered fairly recently and all of it’s mechanisms are not fully understood. Scientists do know it plays a role in appetite and body weight regulation.  Leptin is responsible for maintaining your fat stores at a constant level.  When you lose fat, your leptin levels fall, your appetite goes up and your energy goes down until your fat level is restored.  When you gain fat, leptin levels increase so your appetite falls.. thereby forcing you to lose weight until at the appropriate level of body fat again.

Scientists believe obesity contributes to leptin resistance meaning after being exposed to so much circulating leptin over a period of time, the body stops responding to leptin and you don’t receive the correct appetite signals.  Or, pulling it all together: too much cardio, increases your cortisol which contributes to leptin resistance thereby destroying that important signal from your body.

When TEE goes up UP, NEAT goes down

TEE stands for the thermic effect of exercise.  NEAT is non exercise activity thermogenesis.  You can read more about they factor into your metabolism here.

TEE is all the calories you burn during and after exercise. NEAT is all the activity you do during the day that does not include exercise but keeps you moving, like: walking your dog, going up and down the stairs, gardening, etc.

Remember, your body is trying to protect your fat stores… so if you do way more than your body has adapted to be able to do, it’s going to make you very tired and force you to be sedentary to recover the rest of the day.

A good example of this is a 13 week randomized controlled study.  There was a control group that maintained a sedentary lifestyle, a group that did moderate amount of exercise amounting to 300 calories a day and a group that did a high amount of exercise adding up to 600 calories.

Comparing the two groups to the control, the average energy balance per day was a deficit of 550 calories in the moderate group compared to a deficit of 470 calories in the high group even though the resting energy expenditure (or basal metabolic rate) increased in the high group.  Food intake was not controlled among the groups.

The researchers hypothesized that the higher than expected negative energy balance in the moderate exercisers could be explained by an increase in NEAT.  Meaning, the moderate exercisers moved more throughout the day.  They also suspected the high group consumed more calories to compensate for the extra exercise.

Both groups lost roughly the same amount of weight, leading researchers to propose moderate exercise may increase NEAT without increasing food intake whereas a high amount of exercise decreases NEAT while increasing food intake. 

The Reduction in Metabolic Rate

Studies have also shown the when you combine a reduced food intake and an increased energy expenditure, your body slows its metabolic rate.  This has become known as "starvation mode" leading people to hypothesize in internet chat rooms they are destroying their metabolism or stopped it completely.

Your metabolism is not going to stop as long as you're alive.  When you combine both methods of fat loss for a long period of time, all of those hormonal changes discussed above occur:

  • Your cortisol goes up
  • Cortisol water retention goes up
  • Your leptin goes up
  • You possibly become leptin resistant
  • Leptin resistance leads to a bigger appetite
  • Your food intake goes up without you realizing it
  • Your NEAT goes down

All those factors will cause an apparent weight stall or weight increase despite the fact that you think you are in a deficit. But, you are not burning as much as you thought, you're eating more than you realize, and probably holding onto a lot of water. That is why your weight loss stops.  Your metabolism has not stopped.

Now, your metabolism will decrease by a certain percentage after weeks of a harsh diet deficit and no refeeds. That decrease in metabolism makes it harder to lose weight in combination with all those hormonal factors.  So what do people do?  They do more cardio... they eat less... their cortisol goes up more and a terrible cycles perpetuates.

Research on this issue confirms it,

“It appears that the combination of a large quantity of aerobic exercise with a very low calorie diet resulting in substantial loss of body weight may actually accelerate the decline in resting metabolic rate. These findings may cause us to re-examine the quantity of exercise and diet needed to achieve optimal fat loss and preservation of resting metabolic rate.”

The Best Solution

To lose weight and not experience all the negative physiological changes discussed in this article, the best protocol is a balanced approach.  That’s a lot easier said than done especially when you want to lose fat NOW.  Here are some tips for losing in a way that will cause the least hormonal problems:

1.    Give yourself enough time to lose the fat.  Don’t try to lose 20 pounds in four weeks for your high school reunion.  Give yourself at least 12-20 weeks or more.

2.    Let your diet dictate your fat loss.  It’s a lot easier to drop 500 calories in a diet than add 500 calories in exercise.  Concentrate on your diet first.  It should determine how much you exercise.

3.    Include reefed days to help “trick” your body.  Although this is anecdotal, it appears having one to two high carb/low fat days a week in conjunction with an increase in calories helps to offset some of those hormonal issues seen while dieting down.

4.    Include some form of weight training while dieting to encourage the preservation of lean body mass while reducing fat.

5.    Do not do marathon cardiovascular training sessions.  If you are concerned with heart health, try two to three 30 minute brisk walks a week and maybe one to two 15 minute HIIT sessions depending on your fitness level and goals.  You should NOT be doing 60 minutes or more of cardio a day, every day.  Do not do high intensity work every day and allow at least 48 hours rest between HIIT sessions.

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