Which nutrient has the highest thermic effect of food (TEF)?

• A. Carbohydrate
• B. Fat
• C. Protein
• D. Alcohol

Answer: (C)

Thermic effect of food varies by nutrient because the body expends different amounts of energy to digest, absorb, and process each one. Protein requires the most work: after you eat protein, the body must break it down into amino acids, handle deamination, shuttle and synthesize new proteins, and manage nitrogen through the urea cycle. That extra biochemical activity drives a higher energy cost, often around 20-30% of the calories from protein. In contrast, carbohydrates typically require about 5-10% of their calories to be processed, and fats only around 0-3%. Alcohol isn’t a nutrient, but its metabolism also uses energy; however, its thermic cost is usually lower than that of protein and can vary with context. So protein has the highest TEF among the options.