VLCDs are defined by the National Heart Lung and Blood Institute as diets less than 800 calories per day. An alternative definition of a VLCD is daily calories less than 50% of resting energy expenditure which provides a more individualized calorie prescription. Meal replacements (shakes, entrees, bars, soup, cereal, etc.) are portion-controlled low-calorie foods that facilitate compliance with a VLCD by simplifying food choices and allowing a structured eating pattern. Many studies have shown superior weight loss with meal replacements compared to diets with regular food. Functional MRIs have shown that meal replacements have a calming effect on the brain. One of the reasons that VLCDs are so effective is because they help patients lose weight rapidly. Studies have shown that the rate of initial weight loss predicts ultimate success. Patients who lose weight rapidly in the first 4 weeks of a diet end up losing more weight at 12 months compared to those who lost weight slowly. In one study, patients who lost the most weight at 2 months went on to lose 16% of their body weight compared to <3% weight loss in those who had lost the least in the first 2 months
Slow weight loss is frustrating but fast weight loss is motivating and leads to better overall weight loss.
VLCDs are safe with medical supervision that includes a comprehensive physical exam and labs and an EKG. Intensive support with a dietitian or health educator either individually or in a group format is necessary. Patients receive weekly or biweekly medical monitoring including periodic laboratory testing.
Contraindications to a VLCD include renal or hepatic disease, pregnancy, recent cardiovascular event, active malignancy, severe psychiatric illness, substance abuse and porphyria. Minor adverse effects of VLCDs are cold intolerance, hair loss, headache, fatigue, lightheadedness, halitosis, menstrual cycle changes, change in bowel habits and hyperuricemia. Mild transient elevations in transaminases are common, especially in women. Serious adverse events associated with VLCDs include volume depletion, acute renal failure, electrolyte abnormalities, ventricular arrhythmias, and gallstones. Patients with obesity are already at increased risk for gallstones even before weight loss. Gallstones are three times more likely to have VLCD compared to diets with higher calorie diets. 11-36% of patients on a VLCD develop gallstones in the first 8 weeks, 6% of patients require cholecystectomy. The risk for gallstones can be reduced by including at least 10-15 grams of fat in the diet and by limiting weight loss to less than 1.5 kg per week. Ursodeoxycholic acid (ursodiol) can be prescribed for the prevention of gallstones associated with rapid weight loss.
Patients lose on average 15-25% of their weight in 3-4 months on a VLCD. There are anecdotal reports of patients losing 100, 200 and even over 300 pounds on a VLCD. There can be up to 40-50% weight regain in the following 1-2 years in the absence of follow up care.
Weight loss medications can be used with VLCDs. Although some patients do well start a weight loss medication at the initiation of the diet, another strategy can be to delay initiation for a few weeks when weight loss typically slows down. The idea is that patients who are already losing weight rapidly at the initiation of a VLCD may not have faster weight loss with an antiobesity medication started on day one. But once weight loss slows down, a medication can provide additional support to keep the weight loss going.
The typical duration of a VLCD is 8-12 weeks, although some patients may remain at this diet for 24 weeks or longer. A transition phase of 4-8 weeks gradually adds back vegetables, fruits, lean proteins, and whole grains while still taking some meal replacements. After transition, a long-term behavioral support program is necessary for weight maintenance.
In conclusion, VLCDs using meal replacements are safe and effective for weight loss. Meal replacements enhance compliance because they are portion controlled, filling low calorie foods that reduce decision making. Fast weight loss is better than slow weight loss because initial weight loss is positively related to overall weight loss and long-term weight maintenance. Weight maintenance strategies using antiobesity medications, meal replacements and ongoing support are necessary to prevent weight regain.
