Good endurance and physical fitness mean a high chance of survival! Doctor of Sports Nutrition: Sugar is the key nutrient in sports

Studies show that people with good endurance fitness have a lower mortality rate. What are the factors that affect endurance fitness? This issue of ILSI Taiwan column invites Professor Jiahua Kuo, Dean of the College of Physical Education at Taipei City University, to write an article to analyze the key nutrient in sports - "sugar", and step by step connect the layers of relationship between it and "muscle glycogen", "endurance fitness", and "mortality". Finally, specific suggestions are proposed to increase glycogen storage and improve body shape. Don’t miss out on such wonderful life-like content!

Good endurance and physical fitness, high chance of survival

Early large-sample research results published in the internationally renowned medical journal The Journal of the American Medical Association (JAMA) showed that a person’s exercise endurance can predict future survival chances. This study was designed to measure the endurance fitness of the subjects every five years, and found that the groups with the lowest to highest future mortality rates were: those who maintained good endurance, those who recovered after endurance deterioration, and those who had poor endurance in both tests. The results were consistent for different age groups, including 20-40 years old, 40-50 years old, 50-60 years old, and over 60 years old. The difference in death risk can range from 4 times (over 60 years old) to 10 times (20-40 years old). The two major nutritional factors that determine endurance fitness are water and muscle glycogen. This article only discusses the latter.

Muscle glycogen determines endurance and physical fitness

When the human body is in a resting state, muscles mainly consume fat from adipose tissue, while during exercise, muscles mainly consume a large amount of adenosine triphosphate (ATP). The energy that supports the rapid production of ATP mainly comes from the glycogen stored in the muscles. Although blood sugar will also accelerate the penetration into the muscles when the muscles contract rapidly, the cell membrane transport process is slow and still not enough to meet the urgent needs.

The advantage of glycogen is that it is stored inside the cells. When oxygen has no time to enter the muscles, glycogen can be quickly broken down into glucose and quickly release energy through anaerobic metabolism to maintain a constant ATP concentration in the muscles, allowing the muscles to function normally under high-speed challenges. In contrast, fat cannot be broken down in the absence of oxygen, so it can only serve as the main energy source when the human body is in a resting state. When performing high-intensity exercise with maximum load for more than 1 minute, muscle glycogen determines the quality of endurance fitness.

Starch is the best source of muscle glycogen

The structure of human glycogen is similar to that of starch (note) in plants, both of which are composed of glucose. Therefore, the best way to quickly restore muscle glycogen after exercise is to consume starch. To quickly restore muscle glycogen after exercise, starch is more effective than fructose. Since the muscles have a weak mechanism for fructose absorption, most of the fructose ingested in the diet is absorbed by the liver, and fructose contributes very little to muscle glycogen storage. Therefore, most fructose drinks available on the market are not the best source of muscle glycogenolysis.

High-intensity exercise promotes muscle glycogen storage

Exercise challenges can cause muscles to adapt, that is, consuming glycogen can increase the muscle's glycogen storage capacity. For some people, the muscle can increase glycogen storage by 2 times after 2-3 days of exercise. When insulin is secreted normally after a meal, 85% of the glucose in the body will be stored in muscle tissue. Therefore, the better the muscles' ability to store sugar, the better their ability to control blood sugar.

Generally, relatively static activities such as resting, doing housework, and walking will cause minimal consumption of muscle glycogen. During these micro-activities, muscles mainly consume fatty acids from adipose tissue in the blood due to the abundant oxygen supply. Therefore, if you want to increase the body's glucose storage space after a meal to lower blood sugar, you need to rely on high-intensity exercise. The more muscle groups challenged and the higher the intensity, the more you can avoid storing carbon resources outside of muscles after a meal, such as adipose tissue and liver, thereby achieving the dual goals of "increasing the ability to control blood sugar" and "avoiding abdominal and waist obesity."

Does the “carbohydrate/protein intake ratio” affect life expectancy?

Does the amount of sugar intake affect life expectancy? A well-known study comes from Okinawa, Japan, where the proportion of centenarians is extremely high. Most local people adopt a high-starch, low-protein diet. Interestingly, if Okinawans move to the main island of Japan, their original protective effect against heart disease and metabolic syndrome disappears. Similar evidence was found in a well-known randomized animal intervention study (Geometric Framework for Nutrition), that animals that received a "high-starch, low-protein" diet had the longest lifespan.

The main limitation of human research at present is that there is no randomized control trial report that can prove whether the proportion of carbohydrate (i.e. starch) intake will affect life expectancy. The existing human research evidence is mostly based on grouping after completing a dietary questionnaire and observing the mortality rate of each group after a period of time. Since dietary intake preferences are also highly correlated with many other behaviors that affect mortality, such as education level, smoking, family, etc., it is not the most perfect scientific evidence. In addition, studies with insufficient follow-up time (less than 15 years) will have greatly reduced effectiveness in predicting mortality, cannot establish causal relationships, and are not suitable as a basis for good dietary advice.

At present, we can only say that in studies with longer observation periods, a high-starch, low-protein diet may be a better choice for young and middle-aged people whose weight is slowly gaining. As for elderly people who begin to lose weight after the age of 65, their future mortality rate will be lower if their protein intake ratio is higher. However, it should be noted that a high-starch diet must be accompanied by regular exercise of sufficient intensity. If you eat a high-starch diet every day but do not exercise, you are likely to become obese.

Eat as soon as possible after exercise to enjoy the dual effects of glycogen storage and improving body shape

Endurance fitness is an important indicator for predicting the probability of future death, and the amount of muscle glycogen storage will directly affect how long high-intensity endurance exercise can last (i.e. the quality of endurance fitness). The main food source for rapidly replenishing muscle glycogen after exercise is starch, which is an important staple food for humans and the nutrient source that can best induce insulin secretion. Developing exercise habits can shift this synthesis mechanism to the challenged muscle tissue, allowing the muscle tissue to store more glycogen and protein. At the same time, it reduces the energy storage of other tissues, such as adipose tissue and liver, thereby achieving the effect of changing body shape. It is recommended to perform high-intensity exercise to consume muscle glycogen before the main meal, and eat as soon as possible after exercise and try not to delay. If the meal time is delayed, the two major effects of increasing glycogen storage and improving body shape will be greatly reduced.

(Note) Starch: It is a food ingredient. The best food source is whole grains.

【ILSI Taiwan Columnist】

Guo Jiahua Distinguished Professor

He holds a Ph.D. in Sports Nutrition from the University of Texas at Austin, and is currently the Dean of the College of Physical Education at Taipei City University and Chairman of the Taiwan Society of Sports Nutrition. His research areas include sports nutrition, exercise and obesity, exercise and metabolism, etc.

This article is from the Taiwan International Life Sciences Society column