Which group of substances provides the most energy in an average diet?

The group of substances that provides the most energy in an average diet is fats. Fats are essential for various bodily functions and are a significant source of energy, providing approximately 9 calories per gram. This is more than double the caloric content of proteins and carbohydrates, which each provide about 4 calories per gram.

In a typical diet, while carbohydrates and proteins are important for energy and various bodily functions, fats often surpass them in terms of energy yield. They play key roles not only as an energy source but also in supporting cell structure, hormone production, and the absorption of certain vitamins. Therefore, fats can contribute substantially to the overall caloric intake in a balanced diet.

Vitamins, while essential for health, do not provide any caloric energy, which makes them not relevant when considering energy-providing substances. Carbohydrates are also a primary energy source and play a critical role in metabolic processes, but fats stand out as the highest in energy density. Hence, the correct answer emphasizes the importance of fats as a primary energy source in the diet.