Which nutrient can be used for energy in an emergency if carbohydrates are not available?

The nutrient that can be utilized for energy in an emergency when carbohydrates are not available is proteins. In circumstances where the body is deprived of its primary energy source (carbohydrates), it can turn to its reserves of protein. Proteins are composed of amino acids, which the body can convert into glucose through a process called gluconeogenesis. Though not the body's first choice for energy, this mechanism is vital during emergencies, such as prolonged fasting, intense physical activity, or illness, where other sources of energy are scarce.

Fats are typically used for energy during prolonged, lower-intensity activities but are not as quickly converted to energy as carbohydrates or proteins. Vitamins and minerals play crucial roles in energy metabolism and overall health but do not provide energy directly. Thus, proteins become a significant alternative energy source when carbohydrates are unavailable.