Complex carbohydrates are considered an excellent nutrient source of fuel for endurance athletes because they:

Complex carbohydrates are particularly beneficial for endurance athletes because they offer a sustained release of energy, which is crucial during prolonged physical activity. These carbohydrates, found in foods such as whole grains, legumes, and vegetables, are broken down more slowly compared to simple carbohydrates. This gradual digestion results in a steady supply of glucose to the bloodstream, maintaining energy levels over extended periods without the energy spikes and crashes associated with simpler sugars.

The unique structure of complex carbohydrates allows them to provide both immediate and prolonged energy, making them a vital part of an endurance athlete's diet. This consistency in energy supply helps athletes maintain their performance over longer durations, whereas options that focus on high protein content, essential fats, or vitamins do not specifically address the energy requirements critical during endurance events.

Overall, the sustained energy release is what sets complex carbohydrates apart as an ideal nutrient source for athletes engaged in endurance sports.