Which food has the highest energy content based on primary macronutrients?

The choice of bacon grease as the food with the highest energy content is correct because energy content in foods is primarily derived from fats, carbohydrates, and proteins, with fats being the most energy-dense macronutrient. Bacon grease is largely composed of fat, which provides approximately 9 calories per gram. In contrast, carbohydrates and proteins provide about 4 calories per gram.

When comparing the options, chicken breast is high in protein but relatively low in fat, resulting in a lower overall caloric content. Rice, while a source of carbohydrates, also does not match the energy density of fat. Spinach, being a leafy green vegetable, is primarily composed of water and contains minimal calories from its small amounts of carbohydrates and protein. Thus, bacon grease stands out for its high fat content, and therefore, the highest energy content among the listed foods.