Energy requirements in high-temperature environments
Published Time:
2016-06-14
1. Thermal Energy
At high temperatures, the body's heat metabolism increases. The reasons for the changes in energy metabolism in high-temperature environments are: (1) Increased circulatory system load due to the delivery of large amounts of blood to the body surface for heat dissipation; (2) Increased energy consumption due to the need for a large amount of sweating for evaporative heat dissipation and increased sweat gland activity; (3) Significant loss of body heat due to increased body temperature and sweat evaporation.
There are different understandings regarding the impact of hot and high-temperature environments on human energy metabolism. There is debate about whether energy needs increase or decrease under hot conditions. Some researchers have conducted a series of in-depth studies, emphasizing that the increase in heat energy consumption in hot environments occurs with an increase in body temperature. This helps explain the different understandings mentioned above when observing the impact of high-temperature environments on heat energy metabolism. Regarding the environmental temperature at which an increase in body temperature and heat energy metabolism may occur, some believe that there is a significant difference in heat energy consumption at room temperatures of 37.8°C, 29.4°C, and 21.2°C. Energy consumption begins to increase at 29.4°C and increases significantly at 37.8°C. They believe that there is a threshold between 29.4°C and 37.8°C that causes energy consumption to begin to increase. This observational study has attracted the attention of nutritionists and has changed the previous view that heat energy needs decrease with increasing environmental temperature. Therefore, the US National Research Council revised the heat energy supply standard: in an environmental temperature of 30°C–40°C, an increase of 1°C increases the calorie intake by 0.5%.
The supply of thermal energy can be based on the supply standard formulated by the Chinese Nutrition Society in 1988. When the environmental temperature is above 30°C, for every 1°C increase, the thermal energy supply should be increased by 0.5%.
2. Protein
The effects of high-temperature environments on protein are mainly as follows:
(1) Increased protein catabolism due to dehydration and increased body temperature, as evidenced by increased creatinine excretion in urine, leading to increased protein requirements. If water and electrolyte metabolism and thermoregulation are good, increased protein catabolism will not occur.
(2) Nitrogen loss due to sweating. Sweat contains nitrogen-containing substances such as urea, ammonia, amino acids, creatinine, creatine, and uric acid. Every 100 ml of sweat contains 20–70 mg of nitrogen. Therefore, a large amount of sweating will lead to the loss of a certain amount of nitrogen through sweat.
In high-temperature environments, the body's metabolic processes accelerate, and the breakdown of tissue proteins will also accelerate. Therefore, the supply of protein should be appropriately increased. However, excessive intake should be avoided to prevent an increased burden on the kidneys. The general intake should account for 12%–15% of the total energy, with high-quality proteins such as animal and legume proteins accounting for about 50% of the total protein.
3. Fat and Carbohydrates
There is less research on the effects of high-temperature environments on fat and carbohydrate metabolism. Generally, there is no definite special need for dietary fat, and it should be based on dietary habits and the preferences of the consumer. Some research results show that carbohydrates are important for maintaining endurance and health in high-temperature environments.
Fat should be consumed in moderation, about 20% of the total energy is sufficient, and should not exceed 30%. The proportion of carbohydrates should be increased, generally accounting for more than 60% of the total energy.
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