Final answer:
Fat is the nutrient that provides almost half the calories in fast food, contributing to its high energy density and potential health risks associated with high intake of saturated fat, sodium, and sugary beverages.
Step-by-step explanation:
The nutrient that provides almost half the calories in fast food is fat. Fast foods are typically high in fat, and since fats are energy-dense, providing about 9 Calories per gram, they can significantly increase the caloric content of a meal. In comparison, carbohydrates and proteins each provide about 4 Calories per gram. Fast food meals not only contain a large amount of fat but are also high in saturated fat, sodium, and calories from sugary beverages like soda, which contribute to their high caloric content while often being low in essential nutrients and vitamins.
Excessive intake of these nutrients can lead to health issues such as obesity, cardiovascular disease, and type 2 diabetes. Particularly, a typical fast food meal can have a substantial amount of calories from fat, sometimes exceeding the recommended daily values for total and saturated fats, as well as sodium. For instance, a single fast food meal can exceed half of an adult's daily calorie needs, making it easy to consume excess calories that contribute to obesity and related health problems if one is not mindful of their overall diet and nutrient intake.