Which consistent theme do you hear from most health gurus on how to lose weight? The answer – “Do lots of cardio.” You will hear from just about every diet coach that you should consume fewer calories and do more cardiovascular exercise. It is the age-old 'Get-on-a-treadmill-and-run' mantra. Of course, this advice stems from the belief that your body is an energy balance and that you must burn more calories than you consume in order to lose weight. So what is the result of cardio training?

Exclusive cardio exercises come at a price. Now, when I say cardio, I am referring to cardiovascular endurance training. Key word: endurance . Cardio is long, drawn-out sessions of physical endurance that raise your heart rate for durations of at least 20 minutes (usually 45+ minutes). Examples of cardio exercises include jogging on a treadmill for 30 minutes, a long bicycle ride, swimming for an extended period of time, running more than a 5K, or an hour-long aerobics class. Please note that I am not including sprints into this category. Remember, the duration must be at least 20 minutes to be considered cardio.

So what is wrong with cardio training? Cardiovascular exercises burn muscle while preserving fat! You read that correctly. After an extended exercise interval, your body will burn muscle for fuel, and will later store more energy in fat tissue. From a physiological perspective, this makes perfect sense! Why should your body sport a lot of muscle when you are just moving from one location to another? Basic locomotion does not require much muscle. Your muscles are actually a hindrance: they weigh you down requiring more effort, and they burn calories just to function. Having more muscle boosts your metabolism, which means you burn more calories with the same amount of activity. Now, this may sound great to you (especially if you are trying to lose weight), but it is terrible news to your energy-hoarding body. To adapt to long cardiovascular sessions, your body wants to be as light as possible, while maintaining an energy repository. And what is the best way to store energy? Fat tissue- of course. There are more calories per gram with fat than with carbohydrates or proteins. So, to maximize energy storage and minimize weight, your body stores more fat and burns muscle. This reason explains why marathon runners are not muscular.

Of course, many people fixate on the weight loss aspect. Yes, it is true that cardio can help you lose weight. After all, I just stated that your body wants to minimize the weight to take the strain off your leg muscles. If your goal is simply weight loss, cardio training can help you get there. But simple weight loss is a terrible goal. You will end up like these marathon runners who are underweight but are clinically obese based on body fat (> 30%). High body fat is unhealthy, no matter what your weight is. The takeaway is to focus on more short-term, intensive bursts of exercise and NOT fattening, long-duration cardio training.