A person with a body-mass-index (BMI) over 30, can lose 3 to 5 pounds a week by eating 800 calories a day. This leads to a total weight loss of about 44 pounds if the diet plan is followed for 12 weeks, according to WebMD.
Known as the very low-calorie diet (VLCD), 800 to 1,500 calories per day diet plans are designed for short-term weight loss. They are most effective for obese people and those with weight related medical conditions, such as high blood pressure and diabetes. Very low-calorie diets can lead to side effects such as nausea, constipation, diarrhea and fatigue. Pregnant or breastfeeding women, teenagers, young children and people over 50 years old are advised to avoid very low-calorie diets.