<aside> <img src="/icons/light-bulb_blue.svg" alt="/icons/light-bulb_blue.svg" width="40px" /> The first question to many people’s mind: “How do I have energy without consuming food?”.

The first thing to recognise is that feeling hungry doesn’t always mean you need food energy.

The best way I can describe this is through an example: If one night you let the rope go a little, let’s say it’s the Christmas period, and you feast until your heart's content. The next day, regardless of how much you ate, you will still get hungry. Did all of that food energy disappear? No. It’s still there waiting to be used...

Hunger arises in a cyclical nature at your expected mealtimes.

Should you provide your body with the nutrients it needs while you are eating (the day prior) it’s going to be bottled up, ready to be used when you need it.

Secondly, glucose isn’t the body’s sole source of energy! Fat stores, the body’s secondary source of energy, are also waiting in the back. Using a great analogy by Dr Jason Fung & Jimmy Moore, glycogen stores are like the fridge, always accessible and easy to dive into. Fat stores are like the freezer, except the freezer has a padlock on it, which can’t be opened unless insulin is suitably low.

The more you pry open and use the freezer, the better at it you become. You don’t even have to empty the fridge first! (Metabolic flexibility)

The sheer process of abstaining from food also sets off a series of hormonal responses, including the activation of the sympathetic nervous system, with the release of adrenalin and noradrenalin, cortisol and human growth hormone.

With increased levels of these counter- regulatory hormones, energy expenditure rises.[8] Of course, this is a stress response. Which is why you can certainly “fast too much”.

A Word on Digestion:

Digestion of food requires a lot of blood flow and energy, invested energy, which isn’t returned until the digestion process is over. We all know a good carb crash or food coma; this is a perfect example of energy used towards digestion, overwhelming your energy supply.

When fasting, in the absence of incoming calories, your body’s attention is fully focussed on functioning. Not only this but once you do start to eat, you’re far more sensitive to what you’re consuming as a product of improved insulin sensitivity!

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