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Should you eat before a workout

Oct 14, 2018 | Eat, Move |

We are told that we should eat before a workout because if we are hungry, we won’t have enough energy to move. But is this really the case? Your genes belong to an era 50 000 years ago which was a time when your ancient ancestors did not have the luxury of food availability – hunger was a signal to move and find food.

Eating before a workout

When we eat, protein, fat and carbohydrate is broken down to glucose and a hormone called insulin is produced to pack this energy into the cells.  With this system, we produce one molecule of chemical energy (adenosine tri-phosphate) out of one molecule of glucose – not a particularly energy efficient system. But from the minute we move our muscles do not necessarily need energy from food or the insulin system anymore. New science is showing us that in order to be energy-efficient during different workouts, from high intensity to low intensity, we need to be metabolically flexible.  Being metabolically flexible means that our body can access different energy systems according to need – making us much more resilient. And we don’t necessarily need food to provide with the energy to move.

Not eating before a workout

If your workout involves High Intensity Interval Training (HIIT), there isn’t time for oxygen to get round your body and you cannot sustain your activity for too long.  This is because you only produce two molecules of chemical energy (adenosine tri-phospate)  from one molecule of glucose.  But you are using carbohydrate and at the same time increasing your fat-burn potential as well as producing lactic acid which can be taken up into the brain and converted into energy.

If you want to train at a lower intensity, oxygen gets around to your organs and tissues and you can keep going for longer using your stored carbohydrate, glycogen. The length of time you can keep going at this pace all depends on your glycogen and your capacity to produce glucose from it. Typically the average person can keep going on this system for up to sixty to ninety minutes.

Then if you want to fully engage in endurance activity, rather than topping up your carbohydrate stores with food or gels, by moving on empty your body can shift into fat burning mode by tapping into your fat stores.  And the fantastic news about fat burning is that with one molecule of fat you can produce a whopping hundred and twenty-nine molecules of chemical energy! And fat burns more cleanly than carbohydrate which means you produce fewer damage-inducing free radicals.

Moving on empty

On The In-Sync Diet 6 Step Plan, we recommend you do your exercise on empty to develop metabolic flexibility:

  • Avoid snacking between meals because your body will get too used to the constant top-ups of sugar and you will never switch into burning fat.
  • Whenever possible, have an overnight fast of 12 hours or more. This means if you have your last meal at 7pm you should not eat again until 7 am the next day.
  • Do some HIIT training three times per week for around twenty minutes and twice per week some lower intensity endurance exercise for around an hour. All should be done on an empty stomach.
  • Rather than being a carb junkie, have some protein within sixty minutes of the end of your workout to ensure muscle repair.


By moving on empty i.e. not eating before a workout, you are training yourself to be more energy efficient and resilient.  Being more resilient means that you will find events where you are required to do different types of activity, such as triathlons, less demanding. And don’t forget, this is an evolutionary survival mechanism you have inherited from your ancestors.  It enabled them to be able to cope with periods of famine when they were not able to find food.