Final answer:
The thermic effect of food (TEF) is most significantly influenced by the macronutrient composition of the meal, with protein having the highest effect followed by carbohydrates and fats.
Step-by-step explanation:
The factor that influences the thermic effect of food (TEF) of a meal is A. the macronutrient composition of the meal. TEF is part of the total energy expenditure and relates to the energy required to process food for use and storage. The macronutrients — carbohydrates, lipids, and proteins — require different amounts of energy to metabolize. Proteins have the highest thermic effect, followed by carbohydrates, and then fats. This means that meals higher in protein could have a higher TEF compared to meals dominated by carbohydrates or fats.
Other factors, such as the setting or position of the person eating the meal, do not significantly influence TEF. Additionally, while the total energy expenditure of the individual and the thermoregulation of the room might affect overall metabolism and caloric need, they do not directly impact the TEF of a meal.