Macronutrients: Fat

What are fats?

Ratios of macronutrients have always been under the spotlight, particularly in sports. Fat is the second favoured energy source for the body. Once fat has been digested, it is partly used for energy as fatty acids (FA) and partly stored in adipose and muscle tissue as triglycerides or intramuscular triglycerides (IMTG). When extra energy is needed, triglycerides are broken down in the form of FA and transported via the blood to be used immediately as fuel. 

The breakdown and burning of fat is known as lipolysis and fat oxidation, respectively. The body uses both glucose and fat as fuel at the same time but the dominant source is determined by intensity and duration of physical exercise. Fat oxidation most commonly occurs when glucose is no longer available for energy and the body needs an alternative fuel source.

Fats play a key role in the formation of cells and signalling molecules, insulation, hormonal production and stability, absorption of fat-soluble vitamins, a healthy body composition, cognitive health, joint lubrication and inflammation regulation. All of which are highly important for general health and performance.

The healthiest sources of fats include monounsaturated and polyunsaturated fats (e.g. olive oil; oily fish; nuts and seeds; avocados). Other sources of fat come from saturated (e.g. animal fat) and trans fats (e.g. margarine, heated oil, deep-fried foods, baked goods). 

Most types of fat (saturated and unsaturated) can be synthesized by the body, however, polyunsaturated FA (omega 3 and 6) are essential FA, which require a little extra help. They rely on being consumed in the diet from certain animal and plant sources. Animal sources are the best (e.g. from oily fish), as they can synthesize the fats for us, whereas plant sources require more steps until converted to that found in fish.

Most typically, the average western diet has a much larger proportion of omega 6 than 3. To improve the balance, one should aim to include foods rich in omega 3 such as oily fish (e.g. salmon, mackerel, sardines); almonds; walnuts; flax, hemp and chia seeds and avocados into your diet. 

Fat & endurance performance

Fat is the secondary substrate that powers aerobic exercise at low and moderate intensities. Stored fat in the muscle is highly limited as a fuel source compared to that of carbohydrates and is less sensitive to changes in training volume and intensity (1). 

High fat diets have shown to result in increased fat oxidation to increase adaptations to improve the use of fat as a fuel source during prolonged exercise. This in turn decreases muscle and liver glycogen concentration due to an overall reduced carbohydrate intake (1). Low fat diets, on the other hand, reduce whole body lipolysis and fat oxidation reducing IMTG concentration during exercise (2). Both scenarios can be detrimental to endurance performance.

In order to best support performance and avoid these extremes, fat intake should be around 20–35% of daily caloric intake (3). The daily total fat intake for an endurance athlete does not need to be adjusted with training like carbohydrates and protein. The majority should come from monounsaturated and polyunsaturated sources, the minority from saturated sources and very limited from trans fats.


  1. Jeukendrup, A. E. (2003). High-carbohydrate versus high-fat diets in endurance sports. Schweizerische Zeitschrift Fur Sportmedizin Und Sporttraumatologie, 51(1), 17–23.
  2. Coyle, E. F., Jeukendrup, A. E., Oseto, M. C., Hodgkinson, B. J., & Zderic, T. W. (2001). Low-fat diet alters intramuscular substrates and reduces lipolysis and fat oxidation during exercise. American Journal of Physiology – Endocrinology and Metabolism, 280(3), 391-398. 
  3. Liu, A. G., Ford, N. A., Hu, F. B., Zelman, K. M., Mozaffarian, D., & Kris-Etherton, P. M. (2017). A healthy approach to dietary fats: understanding the science and taking action to reduce consumer confusion. Nutrition Journal, 16(1), 53.

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