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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.
It can be inferred from paragraph 1 that foods high in protein are
选项 A、broken down slowly in the body
B、higher in calories than foods high in fat
C、more flavorful than foods high in fat
D、less energy-dense than foods high in fat
答案D
解析 You can infer that foods high in protein are less energy-dense than foods high in fat. Clues: ...a gram of protein...about four kilocalories of energy. A gram of fat yields nine kilocalories....; ...fat has a greater energy density than.. .protein....
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