Final answer:
The Atwater factor not always included in caloric calculations is 7 kcal/g for alcohol. The Atwater system provides average energy values for macronutrients, but initially omitted alcohol, a significant energy source.
Step-by-step explanation:
The Atwater factor that was not always considered/included in the calculation of caloric content of foods is 7 kcal/g for alcohol (D). The Atwater system utilizes average caloric content values for different macronutrients in foods, including protein, carbohydrates, and fats. These values are derived from bomb calorimetry, which measures the energy content by burning the food. Typically, protein and carbohydrates are considered to have an energy yield of 4 kcal/g, while fat yields 9 kcal/g. In contrast, alcohol wasn't originally factored into this system, though it does contribute 7 kcal/g, making it a considerable source of energy in the diet.
The table referenced suggests different caloric values for certain substances and activities. For example, it notes that carbohydrates and proteins contain about 4.1 kcal/g, which aligns with the commonly used Atwater factors. Understanding these Atwater factors can aid consumers in estimating the energy intake from their diet, allowing for more informed nutritional choices.