Exercise professionals inspire clients to adopt lifestyles filled with regular physical activity, positive behaviors and healthy eating plans. When clients want to lose weight, three dietary approaches often enter the conversation:
- reduced-calorie diet (RCD), a low-calorie approach (1,200–1,600 kilocalories [kcal] per day) that typically involves having a dietitian or clinical nutritionist prescribe a food regimen (Heymsfield et al. 2003)
- meal plan, which uses prepackaged foods and snacks fortified with vitamins and minerals (Heymsfield et al. 2003)
- partial meal replacement, which integrates portion-controlled (vitamin/mineral-fortified) meals into a daily diet of regular foods
This column will explore the scientific literature on meal replacements to help personal trainers determine their efficacy for use with clients.
What Are Meal Replacements?
Meal replacements (see “How to Choose an Effective Meal Replacement” sidebar) may include beverages, packages of shelf-stable and/or frozen entrées, breakfast cereals and meal/snack bars that may be eaten as a sole energy source or with a combination of foods to replace a higher-calorie meal. Commercial meal replacements, often marketed as vitamin-, mineral- and protein-fortified foods, are sometimes combined in an RCD to reach a desired daily caloric deficit (Heymsfield et al. 2003). Products such as Slim-Fast®, Special K®, Lean Cuisine® and many others are meal replacements often marketed to people who are interested in losing weight.
Is a Single Meal Replacement an Option to Consider?
A recent randomly controlled study suggests that the mere substitution of one smaller-portioned meal each day can produce a meaningful reduction in daily energy intake (Levitsky & Pacanowski 2011). Subjects in the study ate their usual breakfast and supper, but for 10 days they chose to lunch on one of the following: Chef Boyardee® pasta, a Smucker’s® Uncrustables® sandwich or a Kashi® snack bar. This one change cut their average energy intake by 250 calories per day (2057 ± 47 kcal to 1812 ± 37 kcal).
Another study investigated the effect of a ready-to-eat breakfast cereal as a nightly structured snack replacement. The research team randomized 25 adults (aged 18–65, BMI ≥ 25) into a cereal and no-cereal group. All subjects reported they were evening snackers. The cereal group had a ready-to-eat cereal with low-fat milk 90 minutes after evening meals, and the no-cereal group members snacked on foods of their choice. After 4 weeks, the cereal group had lost 1.85 pounds, while the no-cereal group had lost 0.39 pound (Waller et al. 2004). Exercise professionals may want to discuss similar options with overweight or obese clients who have evening snacking tendencies.
Heymsfield et al. (2003) emphasize that although many strategies for weight reduction demonstrate promising short-term results, longer-term (≥ 1 year) research still shows a high degree of weight relapse, where clients regain the weight they’ve lost. As a previous IDEA Fitness Journal column stated, research shows that consistent physical activity is the best predictor of sustained weight management after weight loss (Kravitz 2009). Consequently, personal trainers are crucial to helping clients achieve long-term success in weight management.
What Is the Scientific Assessment of Meal Replacement Strategies for Weight Loss?
Use of premeasured, lower-calorie products to facilitate an RCD has proved to be very effective for weight loss (Levitsky & Pacanowski 2011). In a meta-analysis on meal replacements, researchers examined six studies that met strict research methodology criteria. The authors concluded that partial meal replacement programs can be safe and effective; subjects lost about 7%–8% of their initial weight over the course of a year, and weight-related risk factors of disease also improved (Heymsfield et al. 2003).
Will You Be Hungrier on Meal Replacements?
It is tempting to assume that people who consume fewer calories during one meal replacement might compensate for the calorie deficit at a subsequent meal, but this does not appear to be the case (Levitsky & Pacanowski 2011). Although the true mechanism is unknown, Levitsky and Pacanowski propose that people may adapt to the meal replacement as the “norm” for that meal, modifying their behavior in ways that reduce the need to consume more food. Also, visualizing a smaller, portion-controlled meal may help people to slow down while eating and to pay more attention to internal cues of satiety. Future studies are warranted to determine any physiological mechanisms associated with meal replacement plans and appetite.
Are Meal Replacements Safe for People With Type 2 Diabetes?
The Look AHEAD trial (Pi-Sunyer et al. 2007) is an ongoing study of 5,145 overweight subjects with type 2 diabetes undergoing a lifestyle intervention for weight loss. The intervention includes 175 minutes a week of moderate-intensity physical activity plus liquid meal replacements and frozen food entrées combined with conventional foods. One-year results show that subjects have lost an average of 8.6% of their initial body weight, while their cardiovascular fitness has increased by 21%. In addition, some biomarkers associated with metabolic syndrome have significantly improved.
For more about meal replacements, see the sidebar “3 Common Questions About Meal Replacements.”
Applications for the Exercise Professional
Exercise professionals are acutely aware that successful weight loss programs require a multitude of approaches that include regular exercise, behavior modification, healthy nutrition education, portion control and S.M.A.R.T. goal setting for clients. While meal replacements are proving successful at slicing calories from diets and making short-term weight loss possible, exercise professionals have a paramount role in keeping clients motivated over the long haul so they don’t regain lost weight.