**Core Concept**
The thermic effect of food (TEF) is the increase in metabolic rate following the consumption of a meal, resulting from the energy required to digest, absorb, and process nutrients. This concept is essential in understanding how different food components influence energy expenditure and weight management.

**Why the Correct Answer is Right**
Protein has the highest thermic effect among all food components, with a TEF of approximately 20-30% of the daily energy intake. This is because protein requires more energy for digestion and absorption compared to carbohydrates and fats. The increased thermic effect of protein is due to the high energy expenditure of the digestive process, particularly in the small intestine, where protein is broken down into amino acids. Additionally, the body's energy expenditure is increased to process and utilize the absorbed amino acids, further contributing to the high thermic effect of protein.

**Why Each Wrong Option is Incorrect**
* **Option A:** Carbohydrates have a lower thermic effect compared to protein, with a TEF of around 5-10% of the daily energy intake. This is because carbohydrates are relatively easy to digest and absorb, requiring less energy expenditure.
* **Option B:** Fats have an even lower thermic effect compared to carbohydrates, with a TEF of approximately 0-5% of the daily energy intake. This is because fats are relatively easy to digest and absorb, requiring minimal energy expenditure.
* **Option D:** Fiber has a negligible thermic effect, as it is not absorbed or utilized by the body. However, fiber can increase satiety and slow down gastric emptying, leading to a reduction in overall energy intake.

**Clinical Pearl / High-Yield Fact**
When aiming to increase energy expenditure and enhance weight loss, incorporating high-protein foods into the diet can be an effective strategy. This is because protein's high thermic effect can lead to an increase in overall energy expenditure, even at rest.

**Correct Answer:** C. Protein. Protein has the highest thermic effect among all food components, with a TEF of approximately 20-30% of the daily energy intake.