28.17
能量平衡
人体从三种常量营养素中获取能量：碳水化合物、蛋白质和脂肪。当食物中存在的有机化合物的化学键断裂时，能量就会释放出来。食物的能量含量以千卡 (kcal) 为单位，定义为将1千克水的温度升高1摄氏度所需的热量。该值是通过测量食物样本完全燃烧后热量计周围水的温度变化来确定的。
每种常量营养素提供的能量不同…
当碳水化合物、蛋白质和脂肪等有机化合物中的化学键被分解时，能量会被释放出来。
食物能量以千卡为单位进行测量，千卡表示将1千克水的温度升高1°C所需的热量。
该测量值是通过观察已知质量的食物样品在量热计中完全燃烧后，周围水的温度变化来确定的。
每种宏量营养素提供的能量不同：碳水化合物和蛋白质每克约提供4千卡能量，而脂肪每克约提供9千卡能量。
大多数食物都是多种宏量营养素的混合物。高脂肪食物的能量密度较高，如果摄入过量，可能导致体重增加。
当食物摄入量与能量消耗之间达到平衡时，即实现了能量平衡。
如果能量摄入超过能量消耗，身体会将多余的能量以脂肪形式储存，导致体重增加。
相反，如果能量消耗超过能量摄入，身体将动用储存的能量，导致体重下降。
View the full transcript and gain access to JoVE Core videos
Q1: How is food energy measured and what units are used?
Food energy is measured in kilocalories (kcal), defined as the amount of heat required to raise the temperature of one kilogram of water by one degree Celsius. This value is determined by measuring the temperature change of water surrounding a calorimeter after complete combustion of a measured food sample.
Q2: Why do different macronutrients provide different amounts of energy?
Energy is released when chemical bonds in organic compounds are broken down. Carbohydrates and proteins provide approximately four kilocalories per gram, while fats provide nine kilocalories per gram. This difference in energy content reflects the varying chemical bond structures within each macronutrient.
Q3: What happens when energy intake exceeds energy expenditure?
When energy intake exceeds energy expenditure, the body stores the excess energy as fat, resulting in weight gain. This occurs because the body cannot immediately use all consumed calories, so it converts and deposits the surplus into adipose tissue for later use.
Q4: How does the body use stored energy during weight loss?
When energy expenditure surpasses energy intake, the body uses stored energy reserves, causing weight loss. This metabolic shift occurs during periods of caloric deficit, when the body mobilizes fat stores to meet its energy demands and maintain normal physiological functions.
Q5: Why are high-fat foods more calorie-dense than other foods?
High-fat foods are more calorie-dense because fats provide nine kilocalories per gram, compared to four kilocalories per gram for carbohydrates and proteins. Since most foods contain mixtures of macronutrients, those with higher fat content deliver more total energy per unit mass.
Q6: What is energy balance and how does it maintain stable body weight?
Energy balance occurs when there is equilibrium between food intake and energy expenditure, helping maintain stable body weight. This balance is achieved when the calories consumed equal the calories burned through metabolism and physical activity, preventing weight gain or loss.
Q7: How do carbohydrates, proteins, and fats contribute to total daily energy intake?
The human body gets energy from three macronutrients: carbohydrates, proteins, and fats. Each provides different amounts of energy per gram, so total daily energy intake depends on the quantity and proportion of each macronutrient consumed. Most foods contain mixtures of all three, contributing variably to overall caloric intake.