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  3. 1 The three energy-yielding food nutrients are carbohydrates, proteins, and fats. The amount of energy a food provides depends o

1 The three energy-yielding food nutrients are carbohydrates, proteins, and fats. The amount of energy a food provides depends o

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问题 1 The three energy-yielding food nutrients are carbohydrates, proteins, and fats. The amount of energy a food provides depends on how much of each nutrient it contains. When broken down in the body, a gram of carbohydrate and a gram of protein each yield about four kilocalories of energy. A gram of fat yields nine kilocalories; therefore, fat has a greater energy density than either protein or carbohydrates. Foods with a high energy density provide more kilocalories per gram than foods with a low energy density.
2 Different meals may deliver the same number of kilocalories but varying amounts of food energy. For example, a 450-gram breakfast of cereal, milk, fruit, egg, turkey sausage, toast, and jam and a 150-gram breakfast of doughnuts both deliver 500 kilocalories. However, the first breakfast, which is higher in protein, has a lower energy density than the doughnuts and supplies three times as much food energy.
3 During a meal, as food enters the digestive tract, hunger decreases and the body reaches satiation, the signal to stop eating. The nutrient composition of a meal affects the level of satiation the meal provides. Foods low in energy density are more satiating than foods high in energy density. Of the three energy-yielding nutrients, protein is the most satiating and fat is the least satiating. High-fat foods are flavorful, which encourages people to eat more, but they are also energy-dense and deliver more kilocalories per bite. Therefore, eating meals high in fat may lead to overconsumption.
The passage supports which of the following statements about food nutrition?
选项 A、The nutrients in food determine its energy yield and level of satiation.
B、All foods with the same number of kilocalories are equally nutritious.
C、The most nutritious foods are those that are high in energy density.
D、Too many protein-rich foods will lead to overeating and weight gain.
答案A
解析 The passage supports the statement that the nutrients in food determine its energy yield and level of satiation. In fact, these are major ideas in the passage. Clues: The amount of energy a food provides depends on how much of each nutrient it contains; The nutrient composition of a meal affects the level of satiation the meal provides.
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