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Fat vs carbohydrate – powerful exercise fuels and other mysteries

One of the factors that contribute to our exercise performance is nutrition. Genetics play an important role as well as training (how well & how much do you train, etc.), and your overall health.

Fuels necessary to the exercising muscle – stored glucose (glycogen in the liver – can be used immediately when the muscle is active) and circulating glucose – from the bloodstream. Another important fuel is fat – from two main sources – stored fat in the adipose tissue – can be mobilized during exercise resulting in the release of fatty acids into the bloodstream travelling to the muscle and being used as fuel to produce energy. The other source is circulating triglycerides as triglyceride molecules in the blood. These can come through the diet (if you consumed fatty food prior to exercise) or through the liver. Breaking down triglyceride molecules will result in fatty acids to be used as energy source by the exercising muscle.

Simply put, we can say the two main sources of energy in the muscle during exercise are the glycogen stored in the muscle and the fat stored in the adipose tissue, the contribution of these main sources depending on exercise intensity. That is to say the higher the exercise intensity the more we rely on stored glycogen. Your level of training seems to play an important role as well by that if you are well trained you are better able to utilise the stored fat than your stored glycogen.

Using fat as fuel has the advantage of being an unlimited resource as we can store up to 100,000kcal but the disadvantage that it is slow to mobilise and it gives less power as compared to carbohydrates. On the other hand, glucose as fuel has the advantage of giving more power (more beneficial fuel for high intensity exercise) and being locally available but in the same time the disadvantage of being a limited storage fuel, only 2,000kcal.

Practical considerations when endurance exercising:

  • Fill your glycogen stores completely prior to competition;
  • Ingest carbohydrates during exercise if you exercise longer than 45 minutes – 1 hour;

Practical considerations when strength exercising:

  • Fill your glycogen stores completely prior to competition;
  • Consume protein 1.4g/kg;
  • Avoid prolonged catabolic periods – don’t avoid food for an extended period of time as this will result in muscle breakdown which is not desirable by any athlete;


Benefits of regular exercise – Exercise is a very important component of a healthy lifestyle. There are many benefits of exercise apart from weight loss

  • Changes body composition for the better;
  • Increases physical ability and functionality;
  • Reduces high blood pressure;
  • Elevates plasma HDL & lowers plasma triglycerides;
  • Improves insulin sensitivity;
  • Can assist with weight loss;

During exercise people may lose some fat and gain some muscle while their weight might remain constant. They are still benefiting from exercise quite a lot. For instance, frail elderly that have difficulty walking or moving around the house can benefit immensely from exercise, particularly resistance exercise improving their functionality a great deal and prolonging their life in the long run. High blood pressure can substantially be reduced by regular exercise as well!

So, how much do you exercise? How well do you exercise? How is your overall health? What is your improvement plan?

Fat vs Carbohydrate*Nutrition and Health – Part 1 Course – Macronutrients and Overnutrition – Wageningen University, Netherlands

*Nutrition and Health – Part 2 Course – Micronutrients and Malnutrition – Wageningen University, Netherlands

*Introduction to Health and Wellness Course – Arizona State University

*The Science of Everyday Thinking Course – The University of Queensland, Australia

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