Let's make more use of lipids in the body as energy sources and improve endurance!

Exercise requires a lot of energy. Carbohydrates and lipids obtained from the diet are the main sources of energy. The amount of energy stored as carbohydrates in the body is very low at less than one-thirtieth as compared to lipids. However, intense exercise that increases the respiratory rate can lead to fatigue as carbohydrates are not used as the main source. Therefore, we focus our attention on mitochondria that produce ATP using carbohydrates and lipids. An increase in muscle mitochondria makes the use of lipids easier in the body. When lipids are used more often as an energy source, carbohydrates can be preserved and exercise can be continued for a longer time. In this section, we will present the differences in the energy content of carbohydrates and lipids in the body, the mitochondrial functions that use carbohydrates and lipids, and the relationship between mitochondria and endurance.

1. Can the usage the plentiful fat in your body improve your endurance?

Within our bodies, we use the energy obtained from the carbohydrates and lipids that are consumed with our daily diet to perform vital activities and exercise.

Figure 1

Figure 1 shows the difference in the energy sources used in the body depending on the intensity of exercise 1).
Light exercise such as walking primarily uses fatty acids, which is a type of lipid. However, when a person exercises intensely enough to increase his respiratory rate, carbohydrates (glycogen), which are stored in the muscles, are used as the main energy source.

To what degree are the energy sources comprising carbohydrates and lipids present in the body?

Carbohydrates consumed in the diet are stored as glycogen in the muscles and liver. The amount of glycogen depends on the amount of muscle in each person. However, even in athletes, who have higher levels than the general population, only approximately 2000 kcal is stored. About 2500 kcal of energy is required to run a full marathon. Consequently, when carbohydrates alone are used, they are lost during the marathon, making it impossible to run further.

In contrast, lipids are stored as fat in the body. For adults weighing 60 kg with 15% body fat, about 9 kg is stored. The energy content is about 65,000 kcal (calculated as 7.2kcal per 1g). This is more than 30 times of the amount of glycogen.

In other words, if we are able to utilize not only the carbohydrates but also the lipids in the body during exercise, endurance may be improved without being energy-deprived.

1) Romijn JA, Am J Physiol. 1993 Sep;265 (3 Pt 1): E380-91.

2. Mitochondrial function is important in the use of carbohydrates and lipids

How are carbohydrates and lipids used in the body?

We have explained that carbohydrates and lipids are used as energy sources. However, instead of using carbohydrates and lipids in the same form, they are converted into a substance called ATP (adenosine triphosphate). An organelle called a "mitochondrion" in cells acts as a factory to produce this ATP from carbohydrates and lipids 2). (Fig. 2)


2) Turcotte LP, Am J Physiol. 1992 Jun; 262 (6 Pt 1): E791-9.

3. Endurance can increase by enhancing mitochondrial function

Mitochondria in the muscles can increase in size and number when training is conducted, like a marathon athlete. This increase in the number of mitochondria in the muscles makes it possible to use lipids as an energy source during exercise. During exercise, if lipids are used primarily as an energy source, the limited amount of glycogen in the body can be economized (preserved). (Fig. 3)

Figure 3

It is necessary to increase the number of mitochondria in muscles if you wish to improve endurance and achieve optimum performance. When lipids become available as energy sources in the body, it is possible to prevent the loss of carbohydrates, which means that exercise is possible for a longer duration. In other words, it improves endurance.

4. Summary

The following points are important for the effective utilization of energy sources in the body and increasing endurance:

  • ・Carbohydrates and lipids from meals can be used as energy sources.
  • ・Intense exercise can lead to fatigue as carbohydrates are not used as the primary source.
  • ・The amount of carbohydrates stored in the body is low, and the amount of energy obtained from lipids is high.
  • ・The function of muscle mitochondria is important in the use of carbohydrates and lipids.
  • ・If the number of muscle mitochondria increases, lipids can be increasingly used as an energy source.
  • ・Increased use of lipids can preserve carbohydrates, and thus, help increase endurance.

If the number of muscle mitochondria increases, better use of lipids in the body will be possible. To achieve optimum performance, a scientific examination of how to increase endurance should be undertaken tailored to the purpose of the exercise.

▼Here are the amino acids that solve this problem.
The relationship between performance and energy use: Cystine utilizes lipids as an energy source to reduce fatigue


Supervising Editor:Shin Terada


Shin Terada
He has completed the doctorate course at the Graduate School of Human Sciences, Waseda University (PhD – Human Sciences). After holding positions including PD Special Researcher at the Japan Society for the Promotion of Science, Researcher at Washington University School of Medicine, Researcher at Sankyo Co., Ltd., Lecturer at the Consolidated Research Institute for Advanced Science and Medical Care at Waseda University, and Director at the Central Research Institute of Nisshin-Oillio Group, Ltd, in 2012 he became Associate Professor at the Graduate School of Arts and Sciences, University of Tokyo. He also serves as the Chairperson of the Japan Sports Nutrition Association, a specified nonprofit organization, and the Director of the Editorial Committee for the Japanese Journal of Sports Nutrition.

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