What is a metric expression of the energy value in food?

The correct choice as a metric expression of the energy value in food is the kilojoule. In the context of nutrition, kilojoules are used to quantify the amount of energy that food provides when consumed. One kilojoule is equal to 1,000 joules, and this metric unit is standardized, making it widely accepted in dietary guidelines and food labeling.

Kilojoules are part of the International System of Units (SI), which promotes uniformity and ease of understanding in scientific measurements, including those related to health and nutrition. When examining food energy content, kilojoules reflect the energy that the body can obtain from consuming the food, which is essential for understanding dietary needs and managing energy balance.

While calories also measure energy content in food, they are not a metric unit (but rather a traditional unit). Similarly, watts are a measure of power (energy per unit time), and joules represent energy in a more general sense but are not specifically used in food labeling. In summary, the kilojoule is specifically designed for measuring energy in nutritional contexts, thereby making it the most appropriate choice.