Training on empty: a false good idea?

By Dr J.J.M. – sports nutritionist physician

Watch out: the danger of hypoglycaemia during fasted training is real and frequent. Hypoglycaemia (low blood sugar) can occur at any time during your workout, and especially if you haven’t eaten enough the night before and/or if you had a big workout the previous afternoon or evening.

Fasted training: for experienced athletes

Only a careful, consistent athlete, trained in fasted training can optimise fat loss and teach the body to engage in lipolysis (the breakdown of lipids to produce energy). It is necessary to know oneself well; it’s better to loop around the home (so you can go back quickly…), leaving with an energy gel to take at the slightest sign of cravings, and to remember to take a mobile phone in case hypoglycaemia hits you!

The energy systems used during fasted training

If training intensity is too high, the energy system used will be that of carbohydrates rather than lipids, which are used only if the intensity is moderate. Although this is much more complex as the lipid and carbohydrate systems are linked, and the dynamics of how they are used vary a lot depending on the type of sporting activity, but also from one athlete to another depending on the athlete’s level of proficiency and his type of training. And if the body does not find the carbohydrates it needs, it will not look for fats, as I have just explained, BUT the athlete’s own muscle proteins, resulting in an increased risk of micro or macro anatomical injuries.

The synthesis of ketone bodies during fasted training

There is also the risk of creating “ketone bodies”: the body doesn’t find sugar at its disposal since it is fasting, so it will draw on the reserves of certain fatty acids (a form of fat stored in the liver) to turn them into “ketone bodies”. These ketone bodies will get into the blood and make it more acidic (which runs counter to the quality of muscle contraction), with repercussions on the brain as well. This strategy of fasted training can therefore be costly, so much so that a consensus is emerging to discourage this solution.

Adjust your last meal before training early in the morning

On the other hand, for athletes who want to train early in the morning, it is entirely appropriate to eat a suitable and quickly assimilated breakfast, one hour before the start of training. A breakfast designed to meet the specific needs of athletes is ideal and its ingredients are very well suited to the energy intake required.