Final answer:
Fats are the most energy-dense nutrient, providing roughly 9 calories per gram, compared to carbohydrates and proteins, which each offer about 4 calories per gram.
Step-by-step explanation:
The most energy-dense nutrient among carbohydrates, proteins, fats, and vitamins is fats (lipids). The energy density of nutrients is measured as the amount of energy per gram. Fats provide approximately 9 calories per gram, which is higher than both carbohydrates and proteins which each provide about 4 calories per gram. Vitamins do not provide energy in the form of calories. Therefore, fats have the highest energy density, which explains why they are the major energy store for the body and why animals seek lipid-rich food for their higher energy content. Excessive intake of fats can lead to storage of excess energy in fat deposits, potentially leading to weight gain.