Thursday, January 31, 2013

Musings About Fasted Cardio

A lot of people swear by fasted cardio for fat loss. I've traditionally done the opposite. But I've been starting to question my stance on this lately.

So, here's the common argument for fasted cardio:

When you are fasted, your blood sugar levels at the lowest they'll normally be throughout the day. If you then do some exercise in this state, then your body can't rely on sugars for energy, so it'll have to resort to burning fat instead.

And here are the main points I've used to refute this argument:

1. A calorie is a calorie. If you're going to eat 2,000kcal in the day regardless, and you're going to burn 300kcal through cardio regardless, then your weight will change by the same amount whether some of those 2,000kcal are consumed before training or after training. The total calorie consumption and expenditure is the same either way, so it wouldn't matter when you do the cardio.

2. Just because the body doesn't have much sugar to work with, doesn't mean it will use fat instead. It could just use up what little sugar is there, and then you'll topple over experiencing the joys of hypoglycaemia. This actually reflects my experience with fasted cardio.

My experience and my understanding of thermodynamics appears to mute out the arguments in favour of fasted cardio. So why am I starting to consider the possibility that I might be wrong to dismiss fasted cardio?

The main reason is because I've always been one of those guys who thinks that low intensity steady state (LISS) cardio is a waste of time. 'Cus, you know, higher intensities burn more calories per minute and condition your heart and lungs to higher levels of exertion. However, I've more recently come to acknowledge the therapeutic effects of LISS, and the fact that any activity (so long as it isn't harmful) is better than no activity. This has opened my mind up to the totally insane possibility that doing something as simple as going for a leisurely walk might actually be good for you.

By opening my mind to the idea that LISS isn't inherently stupid or pointless, I've also been able to take a step back and consider energy pathways. As a general rule, the lower the intensity of physical work, the higher the percentage of fat is used to fuel the activty, and the the higher the intensity, the higher the percentage of sugar is used as fuel. Traditionally, I've always trained at intensities that use too much sugar to enable safe fasted training. So, instead of my body using extra fat stores to prevent hypoglycaemia, it'll use up the small amount of sugar available and then crash and burn when that sugar is no longer sufficient. Fun times.

On the other hand, if you do some light activity, then perhaps the mobilisation of fat for energy will occur at a more rapid rate than the depletion of blood glucose -- enough to keep it safe while increasing the amount of body fat used before breaking your fast.

The implications of this could be that you lose weight at the same rate as if you'd done the same amount of cardio later in the day, but you lose fat at a greater rate.

Alas, I can't prove whether or not there's merit to fasted cardio, this is just me thinking. Regardless, I think I'm gonna go for a walk now.


  1. The carb argument, joy! Most or all of this you will know.
    Three energy systems the body has, yes? (sorry that was an attempt at Yoda in type)
    Aerobic, lasts a lifetime because when it fails you die. Burns any form of energy including fat which need plenty of O2 to burn. Most common uses in exercise, low intensity (always comparative) majority of recovery.
    Anaerobic, lactic acid system, last until you have to stop through stitch around 90 seconds if used alone in most cases, but can accompany aerobic assistance making the stich happen later. Burns carbohydrate only, fat is too slow to release energy and muscle will be broken down to replace glucose if there is no glycogen left. Exercise uses, moderately high intensity, HIIT etc.
    Phosphocreatine system. Put there by nature for the times when you learn adrenaline is brown, and when you stand up from sitting or lying down. Lifespan normally around 10 seconds, literally lives in the muscles and replaces the lost phosphate from ATP becoming ADP to give you energy directly. Uses in exercise commonly sprints and explosive power work.
    Marathon story. Energy system relaxed and happy as runner is stationary at the start line. Gun goes off body starts moving, energy system has to react fast, only phosphocreatine can be called on this quickly even at this relatively low intensity, a few seconds later anaerobic is ready to take over and aerobic has been summoned, will be ready after its showered and done its hair. The body is used to these demands so it's not long before aerobic is helping out and after a few minutes totally taken over, proof positive aerobic energy is male. Aerobic keeps the runner going burning every energy source available for most of the race. One mile left and the runner kicks up a gear meaning anaerobic needs to help out. Finish line is in sight and there has been someone on the runners tail the whole way so he holds his breath and goes for it recruiting phosphocreatine for the final effort. Across the line breathing as hard as he can the body is using anaerobic for initial recovery dismantling nearby tissue to provide much needed energy until there is enough O2 to start burning fat. The recovery continues when normal breathing resumes aerobic is back in charge, runner goes to the pub for a beer.

    Added complications. There is a finite limit to how much creatine phosphate and glycogen the body will store, some of this is genetic others adaptive from training, unfortunately genes set the absolute limits and are a real git. There is however no limit to how much body tissue in form of muscle or fat the body can create or store, so if there is excess of any kind and the body can convert it to potentially useful fat it will.
    High carb, low carb, high protein, low protein, all been tried by many and can produce weight loss. Balance is best and anyone saying they have the magic formula for perfect balance for everyone is lying. I don’t think I have said that.
    One of the best complications I have used to 'modify' my weight in short term, literally a few days, is high protein. I know that disposing of the excess that will not be converted to fat strips water out of the body, and water is heavy. So when I knew there would be a weigh in and I needed to be a few pounds down I binged on water for a week or so, then used high protein and reduced but still sensible water to knock 4 pounds off my weight in 2 days without strength loss. Of course once off the scales a bottle or so of water put me back over again. I didn't care.

    1. That analysis of the different energy systems sounds about right to me.

      "The body is used to these demands so it's not long before aerobic is helping out and after a few minutes totally taken over, proof positive aerobic energy is male." I had a good little chuckle here.

      I wasn't aware of high doses of protein causing water depletion. You learn something new every time you learn something new.

  2. Free form amino acids are toxins in the body, as with many things we need to survive. Aminos generate ammonia in the body, not good to bleach the internals.
    Excess amino acids are either converted to fat or have to be disposed of, disposal is via urine and the process uses approximately 9 parts water to one protein.
    The body never takes more than a few days to redress this balance once noticed hence many starting high protein diets see weight loss and then gain shortly after. Used well this is great for getting into a weight class you aren't strictly in.

    Here's a mineral you will not see in any supplement but we cannot maintain health without, arsenic. Not something we will ever need to supplement because the incredibly miniscule amount we seem to need is in the soil plants grow in and therefore the plants and animals that eat them. We consume more than needed every day but for reasons no-one fully knows its total absence causes poor health after a matter of weeks.
    The weird part is how this was discovered. There were programs for testing foods that could be taken into inhospitable places, like space and deep undersea. In these places weight and space are at a premium so one truly brilliant idea was wholly chemically constructed food made of only what we need, a mix of sugar, starch, protein, fat, vitamins and minerals. Early signs where good, the food had no real taste, but test subjects were fully functioning. After a few weeks they started to become ill. They were brought out one at a time and each was drawn to an area known to contain trace minerals with only arsenic being outside of their diet, smell and desire led them all to the same place.
    Realising that this was likely one among many things we require in such tiny amounts it would be impossible to detect no further attempts have been made to give all food from non-natural sources.

    1. That's truly surprising. I never anticipated arsenic having positive influences on health.

  3. There are more a few things which have been brought forward, and there is as strong a likelihood for all of them being wrong as there is of any being right. The two I remember are below, long time ago I read it now.
    We are so used to attacking arsenic that is in our system by natural means that if it isn't there the defences put in place attack the body itself.
    We use the trace element to help kill off infections, basically poisoning the invaders.

    I love stuff like this. Strange unexplained and so totally random no-one could have expected it.


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