Eating too few calories can cause dizziness and fatigue.
Although it's possible to lose up to 5 pounds in a week using very-low-calorie diets, VLCDs can actually decrease your body's metabolism. If you're obese and want to reduce your immediate obesity-related health risks by losing more than 2 pounds weekly using a very-low-calorie diet, talk with your doctor to see if this type of medically supervised weight-loss program is a good fit for you. You don't have to use a VLCD to effectively lose weight, however.
Because 3,500 calories equals about 1 pound of body weight, creating an energy deficit of 1,500 to 2,500 calories per day using a very-low-calorie diet can lead to a 3- to 5-pound-per-week weight loss. Most VLCDs contain 500 to 800 calories per day, notes Weight-Control Information Network. In general, creating such a low calorie deficit means your body tries to conserve energy by going into starvation mode, causing your metabolism to decrease and often leading to fatigue.
Because very-low-calorie diets often cause your body to burn fewer calories throughout the day, they are generally no more effective than low-calorie diets in the long term, according to a 2006 review in the journal вЂњObesity.вЂќ Authors of this review suggest that VLCDs can cause greater short-term weight losses than low-calorie diets -- containing 1,000 to 1,500 calories per day -- but these differences are generally not significant after a year.
Although very-low-calorie diets often cause a quick initial weight loss and reduce immediate disease risks in obese individuals, they are only safe under medical supervision, are difficult to adhere to in the long term and may cause negative side effects. Such side effects may include fatigue, nausea, constipation and nutrient deficiencies. Weight-Control Information Network reports that rapid weight loss using VLCDs can also cause gallstone formation and often results in weight regain.
If you prefer to lose weight without medical supervision and keep your body's metabolism as high as possible, a 1- to 2-pound weekly weight loss rate is appropriate, according to the Centers for Disease Control and Prevention. The National Heart, Lung and Blood Institute suggests 1,200- to 1,600-per-day diets are generally safe and effective for many adults seeking weight loss on their own. Your individualized energy needs - for a 1- to 2-pound weekly weight loss - are 500 to 1,000 fewer daily calories than your usual intake.