Final answer:
To calculate kilocalories from nutrient percentages, multiply the amount of each nutrient in grams by its respective caloric value per gram and sum these amounts using the Atwater system.
Step-by-step explanation:
The method for calculating kilocalories from a percentage nutrient involves using the Atwater system. This system takes the average caloric content of proteins, carbohydrates, and fats to determine the energy content. For instance, protein and carbohydrates have an average of 4 kilocalories per gram, while fats have 9 kilocalories per gram. To calculate the total energy, multiply the amount of each macronutrient in grams by its respective calorie per gram value, then sum the results. For example, for a food with 10g of protein, 20g of carbohydrates, and 5g of fat, the calculation would be:
(10g protein x 4 kcal/g) + (20g carbohydrate x 4 kcal/g) + (5g fat x 9 kcal/g) = 40 kcal + 80 kcal + 45 kcal = 165 kilocalories.