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Fats and Why Endurance Athletes Need Them in Their Diets

By Anne Guzman, PCG Nutritionist

Peaks Coaching Group

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Anne Guzman writes:

Fat is a very important element of the diet for an endurance athlete, often undervalued as an important contributor to health and performance in our endurance sports. It is from dietary fats that we get EFAs (essential fatty acids) that cannot be produced in the body. General fat plays many important roles, such as protecting organs. The body requires us to intake fat soluble vitamins DEAK, and fat transports these within the body. Fats are also important in the making of cell membranes, they’re needed to create bile (which helps to break down fat), cholesterol (a type of fat) is required to make important hormones such as testosterone, and fat makes food taste better and helps us to feel more satiated. These are all important functions we need as people and as athletes on a daily basis.

Fats are typically broken down into trans fats, saturated fats, monounsaturated fats, and polyunsaturated fats. It is best to read your labels and avoid both saturated fats and trans fats in your diet. Trans fats, or hydrogenated fats, increase the risk of coronary heart disease by increasing bad LDL cholesterol and decreasing good HDL cholesterol. Focus on getting more mono and polyunsaturated fats from sources such as steamed or broiled fish, nuts, seeds, avocados, flax oil, hemp oil, olive oil, and other poly and mono unsaturated and essential fatty acid oils.

While the body has a limited ability to store carbohydrates, it has a much larger capacity to store fat. Body fat is stored as adipose tissue (the fat visible to the eye) and Intramuscular Triacylglycerols stored in the muscle itself. The total amount of energy that a person is likely to be able to store in carbohydrates is around 2,000 calories. Fat stores can contain over fifty times more energy than that stored in carbohydrates. One gram of carbohydrate has four calories, and one gram of fat has nine.

Carbohydrate stores can be depleted in two hours of moderate to intense exercise. However, an 80kg man with 15% body fat could run at least 13,000 kilometers on his body fat stores. As athletes we would like to be able to tap into our fat stores as much as possible so we can spare our carbohydrates for later in our performance.

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Carbohydrates and fat are always oxidized as a mixture to be used as fuel. Whether one or the other is predominant depends on many factors, including your diet, the intensity of exercise, the duration of exercise, your fitness, and how many carbohydrates you consumed before exercise.

The rate of lipolysis (fat breakdown) in adipose tissue (stored fat) increases when you start exercising. When you begin exercise, you release epinephrine which triggers this increase in lipolysis. On the contrary, insulin inhibits lipolysis. Also, during moderate intensity exercise the blood flow to the adipose tissue is doubled, and blood flow to the skeletal muscle increases greatly, meaning that more FA (fatty acids) are delivered to the muscles for use. The rise in FA concentration depends on the intensity of the exercise. At very intense levels there could be almost no use of FA for energy. The longer you exercise, the more FA are used as an energy source. This could be in part due to the fact that you are depleting your carbohydrate stores.

During lower intensity exercise fat is usually the predominant fuel of choice, but as the intensity increases carbohydrates are the predominant fuel of choice. To be more specific, fat oxidation is optimal at 62%-63%, according to Achten, et al, and when intensity rises to above 75% of VO2max, fat oxidization levels fall to very low values.

With higher intensity exercise, circulation to the adipose tissue decreases, likely due to the vasoconstriction caused by the sympathetic nervous system. Accumulation of lactate may also negatively affect the available FA for use. Fat oxidization is mainly affected by fat availability and the amount of carbohydrate being used. There are several factors that affect FA oxidization. Many are still being studied.

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More recently, attention has been brought to Intramuscular Triacylglycerols, which are fats stored in the muscles themselves. They have been recognized as an important source of energy during exercise. In trained athletes these fats are stored adjacent to the mitochondria and with increased training these numbers increase. Studies have shown that the size of these lipid droplets decreases during exercise to say that we are using them as energy. Dietary fat will replenish these stores. This is yet another reason why it is important for endurance athletes to have good fats in their diets.

We can manipulate our diets in order to teach our bodies to use more body fat as fuel. For example, if you have ever heard that if you train in the morning in a fasted state you will burn more body fat as fuel, this is true. In a fasted state the body will oxidize more FA. However, when you’re in a fasted state, your liver glycogen stores are not maintained, and your fatigue resistance and exercise performance will suffer. The only time I could see this as beneficial would be when you’re just riding easy or in the off season when you’re also at lower intensities and trying to lean out. As an athlete, this tactic while in training will be detrimental to your performance.

As you can see, fats play a crucial part in maintaining energy during exercise. It is important that your diet contain at least 20% of its calories from good fats for both your overall health and your performance as an athlete. This is not a maximum number. Many world class athletes have diets with fat as high as 30-35%. People respond differently to different macronutrient ratios. The bottom line is that athletes are not fat simply because they follow a higher fat diet. Eating fat does not make you fat.

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When building your meal plan, be sure to incorporate enough good fats in your diet. Play around with the amount of fat in your diet and pay attention to how you feel with more fat or less fat. Find what works for you. Remember that fat is a key energy source for endurance athletes and is essential for good health.

Anne Guzman is a nutritionist with Peaks Coaching Group. She is a certified kinesiologist, a registered holistic nutritionist, an AFPA-certified sports nutrition consultant, and a former professional cyclist. Anne can be reached directly through or

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