Using the energy values for foods (see TABLE 3.7), determine each of the following (round off the answer for each food type to the tens place):
a. the total kilojoules in two tablespoons of crunchy peanut butter that contains 6 g of carbohydrate, 16 g of fat, and 7 g of protein

Verified step by step guidance

1. Identify the energy values for each macronutrient from Table 3.7: carbohydrates provide 17 kJ/g, fats provide 37 kJ/g, and proteins provide 17 kJ/g.
2. Calculate the energy contribution from carbohydrates by multiplying the mass of carbohydrates (6 g) by the energy value for carbohydrates (17 kJ/g). Use the formula: $E=m\times e$, where $m$ is the mass and $e$ is the energy value.
3. Calculate the energy contribution from fats by multiplying the mass of fats (16 g) by the energy value for fats (37 kJ/g). Use the same formula as in Step 2.
4. Calculate the energy contribution from proteins by multiplying the mass of proteins (7 g) by the energy value for proteins (17 kJ/g). Again, use the same formula as in Step 2.
5. Add the energy contributions from carbohydrates, fats, and proteins to determine the total energy content in kilojoules. Use the formula: $\mathrm{Total}=E$_carb+E_fat+E_protein.

Key Concepts

Macronutrient Energy Values

Macronutrients—carbohydrates, fats, and proteins—provide energy measured in kilojoules (kJ). Carbohydrates and proteins each provide approximately 17 kJ per gram, while fats provide about 37 kJ per gram. Understanding these values is essential for calculating the total energy content of food based on its macronutrient composition.

Energy Calculation

To determine the total energy in a food item, multiply the grams of each macronutrient by its respective energy value. For example, in the case of peanut butter, you would calculate the energy from carbohydrates, fats, and proteins separately and then sum these values to find the total kilojoules.

Rounding Off Numbers

Rounding off is a mathematical process used to simplify numbers to a specified degree of accuracy. In this context, rounding to the tens place means adjusting the final energy total to the nearest ten kilojoules, which helps in presenting the data in a more manageable and understandable format.