Final answer:
For quick energy in races, long-distance runners should focus on consuming carbohydrates, as they are readily broken down into glucose, which is essential for ATP production and energy storage in the form of glycogen in muscles and liver.
Step-by-step explanation:
A long-distance runner would require quick energy, which can be best supplied by carbohydrates. They are the most common source of energy for our body, readily broken down into glucose, which is the most prevalent fuel for ATP production, the energy currency in cells.
Complex carbohydrates or polysaccharides like starch and glycogen are ideal, especially during the carbo-loading process before a race.
This allows excess glucose to be stored as glycogen in the liver and muscle tissues, providing an energy reserve for endurance activities like long-distance running.