Very low-calorie diets consisting of between 800 and 1,500 calories per day may be effective for quicker weight loss but are not safe for everyone, according to WebMD. These diets may be safe under medical supervision for obese individuals with a body mass index, or BMI, of 30 or higher.
People who are overweight, but not obese, should only follow a very low-calorie diet if they have weight-related medical problems and are receiving professional medical treatment, states WebMD. Side effects of a very-low calorie diet include fatigue, nausea, constipation, diarrhea and gallstones. Rapid weight loss is a common trigger of gallstones, but it is unclear if the cause is due to the weight loss or the calorie restriction.
Consuming only 1,500 calories per day may not be enough for individuals who are following an exercise regime, states the San Francisco Chronicle. Some people are able to lose weight simply by increasing daily calorie burn through exercise, without additional caloric restriction.Consuming between 1,200 to 1,600 calories per day may be effective and appropriate for women over 164 pounds, active women, and most men. Other reports indicate that sedentary women who weigh under 165 pounds following a diet of 1,000 to 1,200 calories per day can effectively lose weight.