Do You Need Fat During Endurance Exercises?

Training for endurance requires plenty of fuel. During endurance exercise, your body relies on energy stored from fats and carbohydrates to go the distance. Understanding how your muscles use stored energy to continually contract will help you eat and train smarter for improved performance during endurance exercise.

  1. Endurance Training and Fuel

    • Exercise scientist Len Kravitz, PhD, defines endurance exercise as the ability to perform cardiovascular exercise for an extended period of time, characterized by the necessity to sustain repeated contractions of the muscles involved in the activity. Two important limiting factors for endurance exercise are your ability to consume and use oxygen, and adequate fuel stores. Both oxygen capacity and fuel use are influenced by training, and to a lesser extent, by diet, hydration and genetics.

    Exercise Energy Recruitment

    • Adenosine triphosphate, or ATP, is the fundamental energy molecule for muscular contraction. While your body can make small amounts of ATP from phosphocreatine and glycogen stored in your muscles, the large amounts of ATP required for endurance activity can only be met by the manufacture of ATP in the mitochondria of your muscles using oxygen, carbohydrates and fats. Your body stores carbohydrate in the form of glycogen in your liver and muscles, but those stores are limited. Fat stored in the form of lipids in your adipose tissue and intramuscular fat provide a more abundant store of fuel for rhythmic long-duration exercise.

    Gender and Fuel Utilization

    • During long-duration rhythmic exercise like running, cross-country skiing, cycling, swimming and other forms of aerobic exercise, women are more proficient than men in recruiting fat for fuel. A study of men and women published in the "American Journal of Physiology, Endocrinology and Metabolism" found that women used proportionately more fat and less carbohydrate than men during endurance exercise, both at baseline pre-training levels and after a seven-week endurance training program. Both men and women used proportionately less glucose and more fat for fuel post-training.

    Diet and Fat Metabolism

    • The type of diet you consume may also have an impact on the degree to which you metabolize fats and carbohydrates during endurance activities. A study published in the "International Journal of Sport Nutrition and Exercise Metabolism" examined the influence of a high-fat versus high-carbohydrate diet on fuel use during endurance training. The researchers found that the consumption of high-fat diets resulted in substantial increases in fat recruitment during endurance exercise, even though subjects consuming both types of diets realized the same overall improvements in performance.