Common sense says that if you want to lose weight, you should lower your calorie intake. But how low can you go? It's important to find a happy medium that will be good for your body. Many people believe that dropping down to 800 calories or less will help shed those extra pounds. However, this type of calorie cutting is neither healthy nor sustainable. People who need to follow a low calorie diet for medical reasons should do so only under the supervision of a doctor. Side effects of calorie-restricted diets include fatigue, nausea, diarrhea and constipation. The recommended daily allowance of calories for an average-sized adult is 2,500.