Non-prescription liquid diets seem to be everywhere. In supermarkets, in pharmacies, in health-food stores and by mail order, powder and premixed liquid formulas can be purchase for far less than the cost of a formula available by prescription only. For instance, Slim-Fast costs less than $1 per serving compared with the typical $100-per-week cost of a medically supervised very-low-calorie liquid diet. And over-the-counter liquid diets are convenient: There are no appointments to keep, no counselling sessions to honor. You’re on your own from start to finish, armed only with manufacturer’s instructions on how to substitute the low-calorie, milk-shake-like formula for one or two meals a day, eat sparingly and exercise in order to lose weight.
If you’re disciplined and follow directions, an unsupervised formula diet can be helpful weight-loss tool, especially if you don’t want to take the time – or don’t know how – to plan and prepare low-calorie “real food” meals that meet basic nutritional requirements.
A Step in the Right Direction
Today’s formulas are a big improvement over those available decades ago. Dietitians and doctors agree that the liquid diets of the 1970’s were dangerous. Their major shortcomings were the ingredients: The protein was of poor quality, and essential minerals such as potassium, which enables the heart muscle to function properly, were missing, as were carbohydrates. A deficiency of the latter can force the body to rely on fat and protein for energy, which can lead to ketosis (an increase in ketones in the body characterized by dizziness and electrolyte imbalance). This promotes weight loss through the elimination of water, but puts stress on the heart and kidneys and in severe cases can lead to death. The fact that people did die while on these diets led to the products’ removal from stores.
Liquid diets now on the market are much more carefully formulated. They include complete proteins (with all the amino acids needed for good health), carbohydrates and fat, and they are supplemented with vitamins and minerals. Over-the-counter formulas are not meant to be total food substitutes, which distinguish them from the medically supervised prescription diets targeted to the severely overweight. The purchaser is instructed to eat at least one low-calorie, real-food meal daily and substitute the formula for the other meals, for a total daily intake of 1,000 to 1,200 calories. In some instances, dieters are also advised to eat fiber-rich foods or take multivitamins.
Just Follow Instructions
“There’s no magic to these formulas,” says Robyn Flipse, a registered dietitian who has a private nutrition-counselling practice in Ocean, New Jersey. “They don’t melt pounds away. You lose weight because of the low number of calories you are taking in.”
The plans can be convenient for people who want to lose a moderate amount of weight – five to 40 pounds, depending on overall weight and body fat – says Dr. Peter Wood, who helped formulate the California Diet, a drink available in department stores. Wood, a professor of medicine at the Stanford University School of Medicine in Palo Alto, California, believes “this kind of diet works because it tastes good, you don’t feel deprived because it includes plenty of carbohydrates [an important source of energy] and it has the recommended daily amounts of balanced nutrients for good health. It also contains fiber, which produces bulk in the stomach and provides a pleasant feeling of satiety.” Wood claims the formulas are a boon for busy people who can’t take time to see a dietitian or calculate nutrients and calories.
“These liquid diets are not only convenient, but because the dessert-like flavor and texture are so pleasurable, they make people feel more satisfied than an ordinary low-calorie diet does,” adds Dr. George Blackburn, an associate professor of surgery at Harvard Medical School and chief of the nutrition/metabolism laboratory at the Cancer Research Institute at New England Deaconess Hospital.
Who’s Keeping Tabs?
Nonetheless, these diets are controversial. Lack of supervision is the first objection raised by dietitians. “People who need to lose 20 percent or more of body weight or who have a preexisting medical problem should have a physical exam before they go on one of these diets,” says Flipse. “It would probably include an electrocardiogram to ensure that the electrical workings of the heart muscle are normal and a complete blood count to check that there’s no mineral deficiency that can be worsened by dieting, harming the heart. People tend not to take these precautions on an unsupervised diet.”
Flipse also maintain that the lack of supervision makes it easy to abuse the diets. “Even people in closely monitored hospital programs sometimes have to stop dieting or modify their diets because of irregular heartbeat, kidney problems or gout,” she says. “Some bodies can’t tolerate a severe method of weight loss or a drastic change in eating habits.” In addition, the diets are off-limits to pregnant or nursing women and people with kidney, heart or liver problems. While the accompanying literature usually cautions such individuals to consult a physician before starting a weight-loss program, some experts feel the point is not made strongly enough – and, again, that the potential for abuse is high.
Blackburn emphasizes that the real value of the new liquid diets is weight maintenance; their use for weight loss requires monitoring. Caloric restriction may affect various bodily systems – blood pressure, heart rate, digestion and endocrine function are likely to change after losses of 10 percent or more of body weight. After each 10 percent drop, Blackburn advises that you visit your doctor for a checkup.
Finally, experts worry about the tendency to overdo formula diets. “People may feel that if a little calorie cutting is good, more is better,” says Marianne Gibbons, a registered dietitian with the Harvard Community Health Plan in Brookline, Massachusetts. “But going below a thousand calories a day for an adult – without medical supervision – can be dangerous. You can lose a significant amount of muscle tissue, not just fat. “
What most consumers are interested in, however, is whether these pals keep pounds off over the long term. “Sure, you’ll lose weight. But as with any unsupervised, low-calorie diet, chances are you’ll regain as soon as you go off the formula and back to the eating habits that may have caused you to be overweight in the first place,” says Melanie R. Polk, a registered dietitian and consulting nutritionist in West Hartford, Connecticut.
Even those who recommend liquid formulas believe that for permanent weight loss, dieters must change bad habits. “Some people walk away when you tell them a liquid diet won’t work by itself,” says Wood. “But if you’re overweight, you have to change your behavior – eat less, exercise more. Nothing you can consume will take off pounds or offset other things you eat.”