Which macronutrient has the highest thermic effect of food?

The correct answer is that proteins have the highest thermic effect of food (TEF). The thermic effect of food refers to the increase in metabolic rate that occurs after ingestion due to the energy required for digestion, absorption, and metabolism of nutrients. Proteins necessitate a higher amount of energy for these processes compared to carbohydrates and fats.

This is primarily because proteins are complex molecules that need to be broken down into their constituent amino acids, which requires more energy and metabolic work. The TEF for proteins can be as high as 20-30% of their caloric content, meaning that if you consume 100 calories from protein, up to 30 calories could be used just in the process of processing that protein.

In contrast, fats have a lower TEF, around 0-3%, as they are simpler to break down and more energy-dense. Carbohydrates also have a moderate TEF, approximately 5-10%. Vitamins, being micronutrients, do not contribute significantly to the thermic effect as they do not provide energy in the same way macronutrients do.