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Slim-Fastis the trademarked brand name of both a line of diet products and a weight-management program known as the Slim-Fast Optima Diet. Slim-Fast Foods, the manufacturer of the diet products, was acquired by Unilever N.V., a company headquartered in the United Kingdom, in 2000. Slim-Fast diet shakes are perhaps the best-known products in the line, which also includes snack bars, meal bars, smoothies, cookies, and powders for reconstituting by mixing with skimmed milk. The Slim-Fast diet plan is sometimes categorized together with other plans based on liquid diet products as a liquid meal replacement or LMR diet. LMR diet products themselves are a major business in the United States, reported in 2006 to account for over $1 billion in consumer purchases each year.
Although Slim-Fast as a specific product was introduced only in the early 1980s, LMR products as a type have been on the North American market since 1960, when Mead Johnson, a company better known as the maker of such baby foods as Pablum and Dex-tri-Maltose, introduced a liquid diet formula called Metrecal. Metrecal was packaged in 8-oz cans, each containing 225 calories’ worth of product. The dieter
(Illustration by GGS Information Services/Thomson Gale.)
was supposed to drink four cans daily, for a total of 900 calories.
Metrecal itself was a rebranded food product originally designed for hospital patients or other invalids unable to digest solid foods. Named Sustagen, the liquid meal substitute consisted of a mixture of skimmed-milk powder, corn oil, and soybean flour, supplemented with vitamins and minerals. When Mead Johnson found that patients reported feeling comfortably full on Sustagen and were satisfied with it as the equivalent of a meal, the company decided to rename their product Metrecal and market it as a diet food in 1960. In the mid-1960s the company introduced Metrecal cookies, nine of which made a meal, as an alternative to the liquid formula.
Metrecal lost much of its market in the 1980s as a result of competition from Slim-Fast, which cost much less and was aggressively promoted in the mass media. In addition to lower price, the original Slim-Fast products tasted much better to most consumers than Metrecal, which had a noticeably chalky taste—so much so, in fact, that one team of researchers in Philadelphia used Metrecal to test its effects on the concentration of gastric acid in patients diagnosed with peptic ulcer. In addition to a more pleasing taste, the original Slim-Fast formula came in a wider variety of flavors and included breakfast and lunch meal bars as well as the canned shakes and a powdered formula that the dieter could mix with skimmed milk at home.
In the early 2000s, Slim-Fast lost some of its popularity due to widespread interest in the Atkins diet. The company replaced the sugar in its original liquid formula with Splenda, an artificial sweetener, and added an additional gram of fat to the formula in order to help dieters feel fuller longer. Another modification to the earlier formula was increasing the proportion of nonsoluble dietary fiber, which also increases the dieter’s feeling of satiety. The new line of Slim-Fast LMRs is called Slim-Fast Optima Hunger Control Shakes. In addition, the company has added several lines of specialized diet products for dieters with lactose intolerance, dieters interested in a low-carbohydrate weight-control plan, and dieters who prefer a high-protein diet. As of 2007, there are five separate lines of Slim-Fast diet products:
The Slim-Fast Optima diet plan is available in a 44-page booklet that can be downloaded from the Slim-Fast website. The booklet explains that the Slim-Fast plan is based on the dieter’s present weight level rather than a one-size-fits-all calorie level or rigid menu. The dieter is instructed to substitute Slim-Fast products for two meals per day, use them for a between-meals snack if desired, drink plenty of
water, and add 30 minutes per day of physical exercise to their lifestyle. The dieter does not have to give up coffee, tea, or other low-calorie caffeinated beverages. The daily meal plans for the four specific weight levels (for adults) are as follows:
Dieters can arrange these meals, snacks, and meal combinations in any daily pattern that works for them. The plan defines its various components as follows:
The Optima diet plan allows a daily calorie count of 1250-1400 calories for a 140-pound dieter and up to 1850 or 1900 for a dieter over 200 pounds.
The Slim-Fast Optima diet plan and the various Slim-Fast products are intended for weight reduction (at a moderate rate approved by most health professionals) or weight maintenance. Some people also use them as convenient and easily portable meal or snack substitutes when hiking or traveling.
The Slim-Fast diet plan has several advantages:
The Slim-Fast products themselves are tastier and appear to satisfy hunger better since their reformulation in 2004. Some studies indicate that the solid bars, however, are more effective in controlling feelings of hunger than the LMRs. An additional advantage is the relatively low cost of Slim-Fast products compared to other prepackaged diet formulas. In fact, Slim-Fast owed its initial success in competing with Metrecal in the 1980s to its considerably lower price. One clinical study of Slim-Fast focused specifically on its effectiveness in helping low-income dieters lose weight, on the grounds that the incidence of obesityis high in this population. The study found that the subjects were significantly more successful in losing weight (7% of body weight on average) with the Slim-Fast plan (2 meal replacements per day plus one sensible meal) than they were when they simply attended a nutrition clinic. However, cost will still be a barrier for some. Typical prices for Slim-Fast products as of early 2007 are $10 for a can of Optima powder (14 servings); $5.79 for a box of 6 snack
bars; $4.29 for a box of 6 cookie bars; and $6.79 for a six-pack of Optima shakes.
Another benefit is that they are supplemented to provide sufficient intakes of minerals and vitamins when consumed in the recommended amounts so micronutrient deficiencies are unlikely to be a problem despite reduced energy/calorie intakes.
In general, women who are pregnant or nursing; adolescents under 18 years of age; and anyone who needs to lose more than 30 pounds and/or has not been physically active should consult their physician before starting any weight reduction program. The Slim-Fast plan and the products themselves, however, are less likely to cause health problems than very low calorie diets (VLCDs) or fad diets. The Slim-Fast plan booklet specifically warns against eating less than 1200 calories per day.
No major health risks have been reported from use of either the diet plan or Slim-Fast products when used as directed.
Published studies of Slim-Fast in the United Kingdom as well as the United States report that it enables dieters who follow the program to lose significant amounts of weight in a safe manner with minimal medical intervention or problematic side effects. One 2002 study of Slim-Fast products as part of weight reduction programs in four high-stress occupations (police, medical professionals, firefighters, and flight crew members) found that the products were effective in reducing weightand body mass index (BMI) even in overweight adults whose stressful jobs would encourage overeating. Four-fifths of the subjects completed the 12-week clinical study and were maintaining their weight loss at six-month follow-up, with the firefighters losing the most weight and the medical professionals the least.
The Slim-Fast plan and products were also shown in a study published in 2001 to be safe and effective for patients diagnosed with type 2 (adult-onset) diabetes. The study of the diabetic patients reported that the subjects showed improvements in blood sugar, insulin, hemoglobin A1c, and blood lipid levels as well as losing weight. The chief drawback reported, as with all weight reduction programs, is patient compliance. About 40% of the subjects in one clinical study of Slim-Fast were excluded from the second stage of the study because they were judged noncompliant. This rate, however, is no higher than the noncompliance rate of subjects on other weight reduction regimens.
Another problem with meal replacements is that they do not necessarily change eating habits so when they are stopped weight regain can occur.
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U. S. Department of Agriculture (USDA). Dietary Guidelines for Americans 2005. Washington, DC: USDA, 2005. Available online at http://www.health.gov/dietaryguidelines/dga2005/document/.
North American Association for the Study of Obesity (NAASO), The Obesity Society. 8630 Fenton Street, Suite 918, Silver Spring, MD 20910. Telephone: (301) 563-6526. Website: http://www.naaso.org.
Rudd Center for Food Policy and Obesity. 309 Edwards Street, Yale University, New Haven, CT 06520-8369. Telephone: (203) 432-6700. Website: http://www.yaleruddcenter.org/home.aspx.
Slim-Fast Foods Company. Website: http://www.slim-fast.com/index.asp. Contact by e-mail only, at http://www.slim-fast.com/contact/comments.asp. Telephone line for nutritional advice: (800) 754-6327.
Rebecca J. Frey, Ph.D.