Most people that consume a mere 500 calories per day lose weight and lose it very quickly. The average weight loss on a very low calorie diet, defined as 500 to 800 calories per day by About.com, is 3 to 5 pounds per week, for a total average of 44 pounds over a 12-week period. However, maintaining the weight loss requires a change in lifestyle.
Most very low calorie diets (VLCD) require medical supervision. However, WebMD warns "VLCDs are no more effective than more modest dietary restrictions in terms of long-term maintenance of reduced weight." Once the patient completes the diet, she requires a change in lifestyle to maintain the changes that occurred.
According to the San Francisco Chronicle, a 500-calorie diet has several potential side effects including fatigue, nausea, diarrhea, hair loss, menstrual irregularities and intolerance to cold. Meals that do not offer plenty of fiber increase the chances of constipation. In addition, such rapid weight loss increases the potential to develop gallstones. The San Francisco Chronicle warns of potential serious consequences, including stroke, heart arrhythmia and brain hemorrhage. Pregnant women following a low calorie diet cause potential birth defects. Diets high in liquid and low in protein decrease blood sodium, resulting in dizziness, confusion and fatigue or even coma and death. Nutrient deficiencies are common, and the Mayo Clinic notes there are much safer ways to lose weight.