The role of carbohydrate intake (glycogen loading) and lipids

Carbohydrates and fats for endurance

The role of carbohydrates in endurance

Total body endurance (endurance), also known as stamina or tenacity, is one of the abilities required in sports competitions. In long-term exercise such as marathons, and sports that involve repeated stop-and-go and long runs such as soccer, endurance is a factor that determines performance.

Endurance is affected by many factors, one of which is the depletion of energy sources. The source of energy during exercise varies depending on the intensity and duration of exercise, but carbohydrates are used as the main energy source. Carbohydrates are stored in large amounts as blood sugar in the blood and glycogen in the muscles and liver, and are used as an energy source only in the amount needed during exercise. Carbohydrates stored in the body are reduced by exercise, and a reduction in carbohydrates can lead to reduced performance and fatigue.

Carbohydrate and lipid energy reserves

The amount of carbohydrates that can be stored in the body is small, and it is said that the amount of energy stored in the body is about 2,000 kcal. On the other hand, lipids are stored as body fat, and it is said that the amount of energy stored in the body is about 65,000 kcal. The amount of carbohydrates and lipids stored varies depending on body weight, muscle mass, etc., but it is clear that the amount of carbohydrates stored is small.

In other words, carbohydrates are used and depleted during sports activities, so they need to be replenished and restored. (It's like gasoline in a car: if you don't refuel, you'll run out of gas and won't be able to drive.)

Supplementing carbohydrates to improve endurance

Recommended amount of carbohydrate supplementation before and during exercise

What is the best way to replenish carbohydrates in order to perform better during exercise? The guidelines are as follows:

<Guidelines for carbohydrate intake during exercise>
1-4g per kg of body weight (1-1g for a 4kg person) 60-60 hours before exercise
1-30g per hour during exercise (for exercise time of 60-1.0 hours)

Timing of carbohydrate intake and meal precautions

Carbohydrates are not immediately used as energy after ingestion, so it is important to consider "what to eat and how many hours before the main exercise (game or race)". Therefore, it is better to consider the time it takes to digest and absorb food, and eat foods that are quickly digested (not necessary) and quickly absorbed as you get closer to the start of exercise. For example, it is a good idea to eat solid foods 3 to 4 hours before exercise, quickly digested solid foods 1 to 2 hours before exercise, and liquids or jellies before exercise.

Carbohydrates are an important source of energy, but it is not enough to just consume a lot of them; you need to consider the amount and timing of your intake. It is a good idea to set up a method for replenishing carbohydrates based on the characteristics of the sport you are participating in.

What is glycogen loading?

"Glycogen loading" is a method of carbohydrate intake in sports nutrition. Glycogen loading is a method that aims to improve performance by consuming a high-carbohydrate diet with a high carbohydrate ratio several days before the target race or competition, thereby significantly increasing muscle glycogen levels above normal.

Modern Glycogen Loading Methods

The latest glycogen loading method involves eating a diet that contains a moderate amount of carbohydrates from one week to four days before the event, and then switching to a high-carbohydrate diet (1% or more of total daily energy intake should come from carbohydrates, 4% or less from fat, and around 3% from protein) three days before. Previously, there was a period during which a high-fat diet with a higher fat content was consumed, but with the latest method, no high-fat diet is consumed.

Sports that benefit from glycogen loading

Glycogen loading is not effective for all sports, but it is effective for sports that involve running for more than an hour or 20km. Therefore, before you begin glycogen loading, consider whether it is necessary for your sport. Also, after glycogen loading, glycogen is stored in the muscles, so your weight will increase accordingly. If you see an increase in weight, it is proof that glycogen is being stored properly, but if your weight affects your performance or you do not want to gain weight before a competition, you do not need to force yourself to do it.

Hopefully you now understand the basics of how important the amount and timing of carbohydrate intake is in endurance sports. Find a carbohydrate intake method that suits you and put it into practice.

*Click here for tips on replenishing carbohydrates before and during exercise

Lipids as an energy source | How they are utilized

Carbohydrates and lipids are mainly used as energy sources for exercise. Let's consider the importance of lipids here.

Lipids are important nutrients for the body, serving as an energy source, a major component of cell membranes, and a raw material for hormones. There are various types of lipids, including fatty acids, neutral fats, phospholipids, and cholesterol. Fatty acids are used as an energy source (neutral fats are composed of glycerin and three fatty acids, and fatty acids are used as an energy source after going through the metabolic process).

Lipids have 1 kcal of energy per gram, making them a nutrient with a higher energy density than carbohydrates and proteins (9 kcal/g). Since sufficient oxygen is required to use lipids as an energy source, they are used as an energy source in moderate or lower intensity exercise, such as endurance sports, rather than in high intensity exercise.

When we talk about lipids in the body, we mean "body fat," and if you weigh 60 kg and have a body fat percentage of 15%, you will have about 65,000 kcal stored. Therefore, unlike glycogen, it will not be significantly depleted with a single activity. The process by which lipids are broken down to produce energy is a little complicated, so it takes longer to use them as an energy source than carbohydrates, but in endurance sports, being able to effectively produce energy from lipids is necessary to improve performance.

Effects of deficiency or excess of fat intake – physical discomfort, weight gain

Many athletes probably think that lipids are a nutrient that should be avoided as much as possible because they are prone to weight gain. However, if lipids are restricted too much, it can lead to a lack of hormones and raw materials for cell formation, which can cause physical problems. For example, if you are on a strict diet and have symptoms such as poor skin condition, you may be lacking in lipids. Except for cases where you are restricting your diet to manage your weight, it is not a nutrient that you will be extremely deficient in. However, you should be careful because unintentionally consuming too much can lead to weight gain.

Research is being conducted into the long-term intake of a high-fat diet as a way to increase energy supply from lipids, but due to various risks, it may not be very practical to carry this out without the guidance of a specialist. On the other hand, it is known that endurance training increases the number of mitochondria involved in energy production and increases the amount of lipid energy metabolism. In order to increase energy supply from lipids, it will be important to take in appropriate lipids and carry out endurance training.

Characteristics of medium-chain fatty acids that are easily used as energy and foods that contain them

On the other hand, there are lipids that are easily used as an energy source. "Medium-chain fatty acids" are easily used as an energy source and have the characteristic of being difficult to convert into body fat. However, many of the fatty acids contained in food are long-chain fatty acids (which take time to digest, absorb, and metabolize) that are difficult to use as an energy source, and there are not many foods that are rich in medium-chain fatty acids.

Foods that contain medium-chain fatty acids include coconut oil, milk, etc. There have been studies that have examined the relationship between medium-chain fatty acids and performance, but in order to fully obtain the effects, it is necessary to properly select the contents of the meal and the types of foods used, and it has been pointed out that the types of sports to which it can be applied are limited.
If you want to consume medium-chain fatty acids on a daily basis, you should limit it to consuming milk and dairy products, and adding a small amount of coconut oil to your beverages. Since it is still a "fat," it may be best to avoid consuming large amounts.

That was all about lipids. Lipids are not easily lacking, but they are an important nutrient for endurance exercise and performance. Let's think about the quantity and quality of lipids we ingest from our daily meals.

*Click here for tips on increasing lipid utilization during endurance exercise

<Supervisor>Shota Sasaki

Lecturer, Department of Health and Nutrition, Faculty of Human Sciences, Hokkaido Bunkyo University.
After completing her doctoral studies in applied life science at the Graduate School of Life Sciences, Kyoto Prefectural University (2011), she obtained her doctorate (academic), and worked as an assistant professor at Obihiro Otani Junior College before assuming her current position in 2019. She is a certified sports nutritionist and registered dietitian. She is also the editor of "Nutrition for Skiers" in the monthly magazine Ski Graphic.

To date, she has provided nutritional support primarily to junior and female athletes involved in speed skating and ice hockey. Currently, she is providing nutritional support to students aiming to become registered dietitians, as well as high school baseball and track and field athletes. Although still in the early stages of development, she is also working on a research project to find nutritional intake methods specific to sports played in cold environments. She aims to be a bridge between research in the field of sports nutrition and the field itself.