Does Fasted Cardio Burn More Fat?

Does it matter for fat loss if you do aerobic exercise in a fed or fasted state?

I didn't know. I have considered the question previously, but up until now I have been sitting on the fence.

On one hand, it makes sense to do light aerobic exercise in a fasted state, most commonly in the morning. Glucose and therefore insulin would be low, due to not eating since the previous evening. Theoretically, this should enhance the mobilisation of fatty acids to be used as a fuel substrate during exercise. 

On the other hand, surely nutrition intake and exercise output over the course of an entire day (or week) is a lot more important than burning more fat in the morning?

Exercise intensity is obviously the key for determine fuel substrate during exercise. The greater the intensity of exercise, the more carbohydrate is used as a fuel substrate. Therefore, if you want to burn a great percentage of fat as a substrate, exercise at lower intensities (especially if following the fasted exercise method).

NOTE: this does not mean that higher intensity exercise does not burn fat. High intensity exercise such as resistance training or sprints causes significantly higher energy output over the same period of time compared to low intensity exercise such as walking. High intensity exercise also has the benefit of excess post-exercise oxygen consumption (EPOC) which can keep energy output higher after exercise, compared to low intensity training.

I'm getting off topic. Do a mix of high intensity and low intensity training, eat well and sleep well and you will be well on the way to your goal physique (it's that easy).

Anyway...

A research paper was just released that looked at the differences in body composition between two groups who completed the same exercise program and had the same diet. The only difference between the groups was whether or not they exercised in a fasted state. The goal of the study was to determine whether or not this made a difference to body composition.

The study found that both groups significantly decreased their fat mass and lost weight. This makes sense, put people on an hypo-caloric diet (energy restricted) and stick an exercise plan and they will lose weight, which is what happened.

So what about the difference between fasted and non fasted groups?

There wasn't one!

Neither group had a significant difference in comparison to the other. This indicates that completing low intensity exercise in either a fasted or non fasted state will have no impact on body composition.

What does this mean for us?

There appears to be no difference, so do whatever you prefer! Overall exercise output and energy intake are more important than feeding time. This means that you don't need to exercise fasted in the morning, which may be beneficial for people who dislike their cardio due to feeling hungry!

I'm off to eat food and do cardio (jokes, I did cardio last week...).


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