Final answer:
The food exchange with the greatest percentage of calories derived from fat is the one that provides the most fat in relation to protein and carbohydrates.
Step-by-step explanation:
The food exchange with the greatest percentage of calories derived from fat would be one that contains a high amount of fat compared to other macronutrients like protein and carbohydrates.
According to the given information, fats are consumed in a ratio of 1:1:4 to proteins and carbohydrates. Since fats should contribute around 20-30% of total calories, the food exchange with the highest percentage of calories from fat would be one that provides the most fat in comparison to protein and carbohydrates.