Which of the following is a main consequence of prolonged carbohydrate restriction?

Prolonged carbohydrate restriction can lead to muscle loss primarily due to the body's adaptive response to a lack of readily available glucose. When carbohydrate intake is significantly reduced, the body begins to utilize other sources of energy, such as fat and, unfortunately, protein. Muscle tissue is broken down to provide amino acids, which can then be converted into glucose through a process called gluconeogenesis. This is particularly prominent in situations where dietary protein is insufficient to meet the body's demands or when energy needs are high, as in intense training or competition. The disruption of optimal muscle protein synthesis due to inadequate carbohydrate intake can impair recovery and muscle maintenance, thereby leading to muscle loss over time.

In this context, the other options do not align with the consequences of prolonged carbohydrate restriction. Improved endurance and increased energy are typically associated with adequate carbohydrate intake, while enhanced recovery relies on sufficient glycogen stores and nutrient availability to repair and rebuild muscle tissue effectively. Therefore, the correct identification of muscle loss as a consequence reflects an understanding of the body's metabolic adaptations to prolonged carbohydrate deficiency.