Underfueling is a form of anxiety and the form of physical as well as mental stress that impacts health and training of a sportsman in a negative way. (From the source of motivrunning.com) Signs of Underfueling Moderate: Constant hunger Fatigue, low energy levels Irritability Intense cravings, or constant focus on food Trouble sleeping Hunger pangs during workouts Gastrointestinal (GI) distress Muscle cramps or weakness Severe: Hypothermia (cold intolerance) Stress fractures Changes in, or complete loss of, a regular menstrual cycle (for women) Significant weight loss The following fueling tips are general, catered to the average population. To understand your individual needs, consult with a sports dietitian. Eat before exercising, especially for high intensity workouts and long runs Eat during exercise if the workout exceeds 60-75 minutes (I generally recommend fueling every 35-40 minutes) Eat after exercising, a recovery meal or snack, followed by another meal or snack within a few ...