Using Fat as Energy During Exercise
Athletes for years have been using carbohydrates as their primary energy source for exercise and performance. Recently an alternative use of energy, fat-burning, has begun to be utilized by athletes as their primary source of energy during sport. Low-carb diets and using fat for energy during exercise can be the same diet, but not necessarily. Using fat for energy is called ketogenesis and can be confused with (ketosis), which is a dangerous and potentially life-threatening state. According to (McGuire & Beerman, 2013, p. 142) the minimum amount of carbohydrates needed for the body, in particular the brain, to function properly is 130 grams. There is some disagreement on this minimum amount of carbohydrates needed for the body to function. Due to the infancy of fat-burning use with modern exercise, research on fat-burning in sport is not as comprehensive at this point to the research on use of carbohydrates. However, there are many proven benefits to utilizing fat for energy and the science on the use of fat for energy is definitive.
Athletic Benefits of “Fat-Burning”
Carbohydrates have been the traditional approach to energy utilization in exercise, but due to the importance of timing and troubles with blood sugar an alternative approach is the use of fat for energy. Athletes, in particular endurance athletes, who want to perform for hours want a sustained energy throughout a long exercise or race session. Your body can utilize its fat stores for energy instead or carbohydrates through the release of ketones into the blood after the process of ketogenesis. “Ketones are organic compounds used as an energy source during starvation, fasting, consumption of a low-carbohydrate diet, or uncontrolled diabetes” (McGuire & Beerman, 2013, p. 292). Three benefits of Ketosis as an athlete include: “metabolic superiority of using fats as fuel, mental enhancement, and health and longevity of controlling high blood sugar” (Greenfield, 2014, p. 327). Use of body fat during sport throughout the process of ketogenesis is metabolically superior because it minimizes nutrient timing that can be a problem during use of carbohydrates for energy. Ketones can be utilized for mental enhancement because ketones have been shown to be a source of energy by the brain. Finally fat-burning can be a great way to control diabetes because blood glucose is not elevating and dipping as can result from use of improper carbohydrates and timing. Blood glucose control and reducing diabetes has been linked to reduction in obesity, cancer, and cardiovascular disease; therefore can be utilized outside of sport for health.
The Traditional Carbohydrate Approach With Performance
From a performance standpoint there is some question over proper timing of carbohydrates prior to exercise, when choosing to utilize a more traditional “carb-loading” way to elevate performance. Ingesting carbohydrates 15-75 minutes prior to exercise, can result in a “rebound hypoglycemia” resulting in a tired feeling, low energy, and ultimately poor athletic performance (Jeukendrup & Killer, 2010, p. 19-21). However, having carbohydrates less than 15 minutes or during warm-ups before exercise are linked to better performance, when utilizing the carbohydrate load way to performance, (Jeukendrup & Killer, 2010) For the non-athlete, the previously mentioned rebound hypoglycemia would be the low-energy feeling or tiredness one feels after a big meal. As a result of the (Jenkendrup & Killer, 2010) article, it is recommended that when choosing to utilize carbohydrates for athletic performance to choose low glycemic index carbohydrates preventing hyperglycemia and hypoglycemia incidents for the non-diabetic athlete, “ingesting carbohydrates just before exercise or during the warm-up” and “avoiding carbohydrate in the 90 minutes of exercise altogether. Due to the issues related to carbohydrate ingestion, hypoglycemia, hyperglycemia, and importance of timing; many endurance athletes have transitioned into a fat-burning approach. However, there is no proven “performance enhancement” benefit of fat-burning over carbohydrate burning; if carbohydrate timing is done correctly according to (Ormsbee, Bach, & Baur, 2014, p. 1782).
When fasting the body uses fat for energy and when done properly can be a great way to lose weight for the obese. Ketogenesis utilizes body fat and spares uses of amino acids which results in weight loss without loss of muscle tissue. However, when a fast lasts too long or the exercise during a fat burning state is too prolonged muscle wasting and ketone levels resulting in high blood acidity can occur, which can be very dangerous (McGuire & Beerman, 2013, p. 293). You can get mental enhancement from ketogenesis, but it typically takes the body 10-14 days for the body to adapt to fat-burning according to (Greenfield, 2014, p. 327). FInally, there is no proven performance advantage of fat-burning compared to properly timed carbohydrate use (Ormsbee, Bach, & Baur, 2014, p. 1782). When done properly fat-burning can be: convenient, a good weight loss strategy, utilized for blood glucose control, and utilized for endurance exercise.
Greenfield, Ben. (2014). Beyond training: Mastering endurance, health, & life. Las Vegas: Victory Belt Publishing, Inc.
Jenkendrup, A.E. & Killer, S.C. (2010) The myths surrounding pre-exercise carbohydrate feeding. Annals of Nutrition & Metabolism 57(2). 18-25 doi:10.1159/000322698
McGuire, M. & Beerman, K.A. (2013) Nutritional sciences: From fundamentals to food. Belmont, CA: Wadsworth.
Ormsbee, M.J., Bach, C.W., & Baur, D.A. Pre-exercise nutrition: The role of macronutrients, modified starches and supplements on metabolism and endurance performance. Nutrients 6(5), 1782-1808. doi:10.3390/nu6051782
Volek, J. & Westman., E.C. (2002). Very-low-carbohydrate weight-loss diets revisited. Cleveland Clinic Journal of Medicine, 69(11), 849-862. doi:10.3949/ccjm.69.11.849