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“As a pre-med I’ve heard from other people that they like to carbo-load before tests and it actually helps out.”

College students as a whole are commonly stressed and cramming for their exams the night before. Pre-medical students are even more notorious for doing anything to get ahead, as grades are incredibly important to as part of the application process to medical school. It is not surprising that some people treat test-taking like an athletic event that merits carbo-loading. I have heard of pre-med students that have snapped during exams and gone around ripping up people’s answer sheets in the midst of the exam.

Carbo-loading is common to many athletes because carbohydrates are biological molecules that provide quick energy for the body. The molecules are stored as glycogen in the muscle and liver after a large meal, and are rapidly consumed during exercise. Therefore, athletes can effectively prepare for their event by storing more energy for greater endurance the next day.

These pre-med students probably hope to store more energy in order to promote clearer thinking the next day during the exam.

See:
Bergström, J., Hermansen, L., Hultman, E., & Saltin, B. (1967). Diet, muscle glycogen and physical performance. Acta Physiologica Scandinavica, 71(2‐3), 140-150.