1. No energy

Are you always in need of a cup of coffee? Do you ever feel tired, even after getting enough sleep? One sign you are not eating enough is a low energy level. Studies have shown not eating enough calories is associated with insufficient energy. Moreover, other studies suggest female athletes who do not consume enough calories throughout the day have too little energy to support the elevated level of physical activity. It is important to know that an increase in activity level requires an increase in calories.

Businessman sleeping in office. The fatigue from workmanop1984 / Getty Images