Optifast and Medifast are very low-calorie diets for very overweight people, according to "Liquid Diets," a Vanderbilt University report. In the 1970s, liquid diets caused "at least 58 deaths," according to the textbook "An Invitation to Health." However, Vanderbilt reports that liquid diets have "drastically improved" since the 1970s. Optifast and Medifast are two of the most effective liquid, low-calorie diets because they combine calorie restrictions, exercise and behavior modification classes, the Vanderbilt study concluded.
Optifast and Medifast are classified as very low-calorie diets by medical researchers because participants eat 420 to 800 calories daily during the first three months of their programs. The calories come primarily from liquid shakes. The Merck Manual of Medical Information recommends that you eat 1,600 to 2,400 calories daily to have the energy for daily activities. Eating far fewer calories jeopardizes your health unless you are very overweight. The second and third steps of Medifast and Optifast are resuming eating meals and maintaining your weight loss.
Medifast, Inc. and Optifast.com recommend consulting a doctor before starting any weight-loss program. The National Academies Press reports that Optifast won't permit you to join its program unless you weigh at least 50 pounds more than your desirable weight as defined by your body mass index, while Medifast requires you to be at least 30 percent overweight. Both companies prohibit pregnant and lactating women and have other health-related restrictions. Medifast also won't let people who have eating disorders or aren't physically mature join.
Optifast and Medifast both make special products for their beginning dieters and call their products meal-replacements, but they offer different choices. Optifast produces liquid products such as 100-calorie high-protein drinks with a caramel or strawberry flavor and supplements its drinks with nutrition bars such as 90-calorie lactose-free chocolate bars. Medifast also emphasizes shakes, other drinks and soups, but it also produces chili, oatmeal, scrambled eggs, stew and several snacks, including cheese puffs, pretzels and pudding.
Optifast and Medifast diets become less effective over time. Optifast reports that people typically lose 52 pounds in the diet's first 22 weeks. Medifast reports that people lose 2 to 5 pounds weekly during the diet's 16-week weight-loss phase. Vanderbilt's study reported that the 61 percent of Optifast dieters who remained on the diet for 19 weeks lost an average 51 pounds, but they regained an average 40 pounds within 54 months. The report lacked data on Medifast dieters, but concluded that very low-calorie diets have "restricted long-term success."
Medifast, Optifast and other liquid diets that are being offered today are superior to their predecessors because they contain more carbohydrates, protein, minerals and vitamins, reports "An Invitation to Health." Early liquid diets were "basically starving the people," according to the Vanderbilt study. Despite the improvements, you should exercise if you go on an Optifast, Medifast or other liquid diet and want to maintain your weight loss. Non-exercisers regained seven times as much weight as exercisers, reported Vanderbilt.