Any of my personal trainers will tell you that “Richard isn’t a fan of Aerobic exercise”.

Sure, I ride 30-50K a week on my bike, because I don’t drive and Batemans Bay is a nice place to cycle around.  But actual cardio like running on a treadmill, rowing on a stationary rower, or stationary cycling?  I have always found that boring, not to mention painful on my knees and ankles – it just makes me tired and hungry.

Aerobic exercise for as long as you can at 55%-65% of your maximum Heart rate (AKA the fat burning zone) is supposed to be the best way to burn a lot of energy.  Right?

Increasing your Energy Output

If you believe in the Energy Balance hypothesis of weight management, then you will “know” that if you want to lose weight you have to exercise more.  Get your fat ass off the couch and go for a run.

But is any of that “common sense” wisdom actually true?

As I outlined in Why you get fat, there is another equally likely (Hormonal) theory of weight management – that sloth and gluttony are not the causes of obesity, but are the necessary biochemical results of insulin resistant people in the presence of a diet high in carbohydrates.

The following is a 1 hour lecture by Gary Taubes to Cornell Medical students on the subject, and is one of the best explanation of both hypotheses.

So what does Science say?

Right now there is very little experimental evidence to show which theory of weight management is actually correct, but there are apparently multiple studies underway that aim to test these theories.

Let’s say however, for the sake of argument, that you want to increase the energy you use.  The question then is will doing Aerobic exercise actually be beneficial to our weight loss.

The effect of Cardio on Weight loss

Consider the following study [ Effects of aerobic exercise on energy expenditure and nitrogen balance during very low calorie dieting : Phinney et al];

The researchers locked 12 overweight patients in a Metabolic ward for 4-5 weeks, where every single calorie they ate and expended could be measured.  The participants were fed 720 kCal/day with enough protein to maintain muscle mass (1.5g per kg of ideal body weight).  The candidates were then split into 2 groups

• The control group were completely sedentary for the entire time
• The intervention group performed 27 hours of supervised Cardio

Common sense would tell you that the intervention group burned more Calories and ate the same amount so they should have lost more weight.  Right?

Results

Controversially, both groups lost a similar amount of weight in 4 weeks, 6.5kg for the exercisers, 6.9kg for the couch potatoes.

So how can they lose more weight, if they did less exercise?

Well the researchers measured the actual energy use of the participants every moment of the time they were in the ward, both when they were on the treadmill and when they were at rest.  For the first week the resting energy expenditure (REE) of both groups dropped by 10% – meaning the amount of energy their bodies used when they were just lying on a bed trying to not do anything dropped by 10% in response to the Calorie restriction.  After the first week the REE in the control group (Couch potatoes) stayed at that new level for the remainder of the experiment.

Where it gets very interesting is that the REE of the Intervention group (Exercisers) continued to drop by a further 17%.

Analysis

So what apparently happens is that when you restrict your food calories (diet) and do Cardio for as much as 2 hrs a day, it will have no net effect on your weight loss because your own bodies homeostatic energy regulation mechanism will conspire to make you lose fewer Calories in the 22 hrs a day that you aren’t running on the treadmill.

The good news for me is that I don’t have to do any Cardio and it won’t have any effect on my weight loss.  Weight loss aside, there is a benefit to doing a little Cardio, which is why I keep my Aerobic exercise to less than 30 minutes a day (cycling) or short duration High Intensity Interval Training (HIIT), have alternate day rest days, and have started doing more weights to build muscle mass which definitely increases REE.

But I don’t have to do Cardio for weight loss.

WOOT!