What is the primary energy source in a diet that provides 4 cal/g?

The primary energy source that provides 4 calories per gram is carbohydrates. Carbohydrates are the body's main source of energy and are commonly found in foods such as grains, fruits, vegetables, and legumes. When consumed, carbohydrates are broken down into glucose, which is utilized by the body for immediate energy or stored for later use.

Proteins, while also a crucial macronutrient, primarily serve as building blocks for the body's tissues and are generally not used as a major energy source unless carbohydrate and fat intake is insufficient. They provide approximately 4 calories per gram as well, but their primary role is not energy provision.

Fats are another important energy source, providing about 9 calories per gram, making them more calorie-dense than carbohydrates. Fiber, though vital for digestive health, is not a significant source of energy in diet, as it is not fully digested by the body.

Overall, carbohydrates are recognized for their significant role in energy provision, especially in the context of a balanced diet, contributing to both short-term and long-term energy needs.