Exercise is more effective on an empty stomach, but proceed with caution

There’s no such thing as the perfect exercise regime for people trying to get in shape. No magic formula that tells you how much time to spend running on a treadmill as opposed to lifting weights.

There are, however, things you can do to get the most from your workout session.

Recently, scientists have studied the use of fasting as an exercise aid, and the results are promising. The research suggests that working out on an empty stomach does increase the rate at which fat is burned.

The overly simplistic ‘calories in-calories out’ model can’t explain this phenomenon. But the observed endocrine effect of prolonged fasting and exercise (insulin sensitisation, increased growth hormone release, mobilisation of glycogen and fat stores) can.

We know that high intensity exercise training (HIIT) elevates resting metabolism for up to 18 hours after a workoutWhat we didn’t know until now is that exercising while fasting brings about changes at the molecular level too. In other words, fat will continue to burn more efficiently long after the end of a session at the gym.

During one study, 10 men between the ages of 18 and 35 with ‘increased central adiposity’ (that’s extra belly fat) were recruited. Half were made to fast for 12 hours, and half were allowed to eat a breakfast high in refined carbohydrates . They then spent 60 minutes doing moderate intensity exercise on a treadmill.

Blood samples were taken both before and after test, as well as fat biopsies from the abdomen, which were then analysed. 

The results were interesting; fat and carbohydrate oxidation (indicating breakdown of stored body fat and glycogen) was significantly higher in the fasting group; what this means is that exercise in the fasting state burns more fat.

At the molecular level, it was found that genes responsible for lipid metabolism, insulin signalling and mobilisation of glucose in adipose (fat) tissue were activated more profoundly when exercise occurred in the fasted state.

Proponents of ‘fasted exercise’ have been saying this for years. Now there’s robust evidence for their claims. The research also shows that the positive effect may persist for some time, meaning that a mixture of fasted and ‘fed’ workouts could potentially yield similar results in terms of body composition. Further studies will be required.

I would advise anyone interested in trying fasted workouts to do so after consulting a doctor, particularly if they have chronic health conditions. Everyone is different, and for some people this type of exercise isn’t going to be ideal. Adequate hydration is essential. Drinking water doesn’t break a non-religious fast as the dietary endocrine effect is non-existent. I would also advise them to eat a healthier breakfast than those served in this study, which were too high in refined sugar.


  • dandelion

    HIIT actually means ‘high intensity interval training’. But never mind: the extra I is a nuisance anyway: how are we supposed to pronounce it?

    • Tarek

      Thanks for the correction. Pronounced “HIT”

      • dandelion

        Thanks: that’s how I’ll say it!