The first symptoms dieters on low calorie diets may experience are a lack of energy and mood changes. As you cut calories, your body will have less food to convert to energy. The levels of sugar in your blood will typically drop, and this can lead to fatigue, irritability, and even food cravings. Some people who plan to cut back on food actually find themselves cheating on their diet because of the strong cravings for unhealthy foods that can result from extreme hunger.