The short answer is – Absolutely NOT. But how is that possible when almost everybody knows that if you want to lose weight you need to do cardio. Let’s have a look.

What is a cardio workout?

It’s a type of aerobic training, which means all the cells in our body use oxygen to create energy to meet the demands of the workout.  It does so because the energy output required isn’t that great at a moment of time (such as in heavy lifting) so the cells are able to get enough oxygen for respiration and creation of ATP (energy). Now using fat and binding it with oxygen is a slower process, and because LIIS isn’t that intense, meaning that the lungs can keep up the pace with the cell’s requirements – the body can oxidise fat. Conversely, in the case of heavy lifting or HIIT training, the energy output is rapid and great, the cells don’t have time to get the oxygen, thus the body must rely on burning the sugar (glucose).

The notion of cardio being favourable for fat loss is derived from the fact than when we are working in around 60-75% of our maximum heart rate, the body can oxidise fat. For anything more intense, it will have to burn sugar (Why we need to train for type of training we do – article read here). But, hang on…

This is where it gets interesting.

The fact that STEADY STATE CARDIO can use fat for fuel, DOES NOT mean it BURNS BODY FAT! In fact, it has been shown that the fat burning effects of anaerobic training exceeds that of an aerobic one.

How and why?

Well during HIIT or intense weight session, your body will use glycogen (type of sugar stored in your muscles) and the harder the session – the more glycogen will be used. Now, once the session is over, studies show that up to 36h after, the body must run faster (faster metabolism) to replenish the glycogen storages. It will then pull the fat form adipose tissue (fat) and make sugar for the muscle cells again.

Furthermore, log duration cardio workouts are extremely catabolic, as this is a type of workout where the body doesn’t require large developed muscle mass; So, if done frequently, or inadequately periodised, the body will use some of it (catabolism). Think of long – distance runners, have you ever seen a very big – muscular one?

Now, in terms of calories, yes you will expend maybe more calories on a long cardio session; which will then put you in a larger deficit, but you can achieve this by playing with calories and aerobic training, plus get the prolonged benefits you get post anaerobic –  training.

Take home message

Cardio isn’t necessary for fat loss. It’s the energy balance that will determine this. LIIS training can put you in a deficit sooner, calories equated, but anaerobic training will speed the fast burning processes for much longer after the session is over.