Eating To Fuel Exercise

I was having a discussion with one of my clients the other day about eating prior to exercise. I was emphasising the importance of eating at least a little something prior to strenuous exercise and in return she asked, “well, what exactly should I be eating?”.

The Importance of Eating Prior to Exercise

Firstly, I want to stress how important it is to ensure you are eating prior to completing strenuous exercise. During my time in personal training there have been numerous occasions where, during strenuous activity, I have either had to cut a session short or ask an individual to take a break as they beginning to feel light-headedness and dizzy . Typically, by lying them down and elevating their feet (raising them above the level of the heart) the symptoms they experience soon pass however, 9 times out of 10 when I enquire when the last time the individual ate, they either have not eaten or have not eaten for an extended period of time.

To sustain exercise, you require glucose. Glucose is blood sugar which your body can synthesise itself, however, glucose levels are significantly impacted by ones diet and meal timings. If you don’t eat for a prolonged period of time or don’t eat any breakfast prior to exercise, your glucose levels be very low. In simple terms, your body will be depleted of fuel and therefore the body will struggle to maintain normal functions and cope with the demand of strenuous exercise.

A very common training method for weight loss is fasted cardio. Based on the above information you may be beginning to understand why I would not recommend fasted exercise.

Click here to read a previous article on fasted cardio.

Recommendations for Eating Prior to Exercise

Eat a proper meal at least 2 to 4 hours prior to exercise as this will allow the digestion process to begin to take place, allow the meal to settle and most importantly will boost your blood glucose levels significantly helping avoid hypoglycaemia (low blood sugar) when it comes to exercise. If you eat a large meal too close to an exercise session, it can make exercise uncomfortable and can also lead to dizziness. This is because your body is beginning to digest the large meal and therefore blood is being concentrated to the digestive system rather than the working muscles.

If this is not possible, my recommendation would be to eat a small snack prior to exercise. And it can literally be anything – within reason. I’m not saying have a small bag of greasy chips from the chip shop next door before your session. Some healthy examples: nuts, fruit, granola, yogurt, crackers, rice cakes or bread.

High GI v Low GI

The Glycaemic Index is a number which ranges from 0 to 100 that will help us understand the impact that a certain food will have on our blood glucose levels. If the number is low, it would indicate that the food will not have a significant impact on blood glucose whilst a higher value would indicate that it will have a more substantial impact.

GI Values: 0 to 55 – low, 56 to 69 – medium, 70 to 100 – high


The Impact of High/Low GI Foods on Blood Glucose



There has been a lot of debate about whether you should consume foods that have a High GI or Low GI prior to exercise. There have been numerous studies look whether it is more beneficial to consume a high or low GI meal to maximise performance. The studies indicate that it actually does not matter whether you consume high or low GI foods before exercising. However, consuming a meal or food source with a high GI post-workout has been found to rapidly restore glycogen stores (energy) in the muscles.

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