Meal replacement plans such as Slimfast and Medifast have been around a long time now. Is there any evidence on their effectiveness? The hesitant answer is yes. Why hesitant? Many of these studies are funded by these vendors. Certain populations are excluded that are very important in today’s society.
In a 2010 publication, the VP of Scientific and Clinical Affairs at Medifast was the lead author on a study of adults aged 18-65. Both diet plans were restricted to 1000 kilocalories a day, a seemingly good recipe for success to begin with. Early weight loss favored the meal replacement plan (12.3% vs. 6.9%). At week 40 there were no significant differences in the BMI reduction (7.8 vs. 5.9%) nor the biochemical markers studied.
A 2004 study was funded by Slimfast and also focused on adults aged 20-65. Here, again, both groups lost weight. The authors noted that the meal replacement plan subjects found it easier to understand and follow the food amounts.
A 2007 study funded by Slimfast found mean weight lost was not difference between groups. The low calorie group lost 8.4% of their original weight and the meal replacement group lost 6.2%. Both groups reduced calorie and fat consumption and increased protein intake over one year. Women 50 years and under were the subjects.
Ahrens was another Slimfast funded study from 2003. Again, both groups lost over 5% of their base body weight, the marker of significant body weight reduction set by the CDC. Further, there were no differences in biomarkers, including blood pressure, cholesterol, triglycerides or lipids. This study spanned 22 weeks.
A 2003 meta-analysis was provided by a member of the Slimfast nutritional institute. This meta-analysis combined six studies but two of these included diabetics that may have been quite different. Again the age was limited to those under 65. 88% of the population were women. Attrition was a problem in many studies and sometimes approached 50%. All six individual studies showed significant weight lost in both groups. Pooling the data had interesting results. More participants lost over 5% of their baseline body weight in the meal replacement group p<0.0001) at one year. The low calorie diet group lost between 2.61 and 4.35 Kg and the meal replacement plan lost 6.97 to 7.31 Kg and this difference was statistically significant. Was this influenced by including the diabetic patients? We do not know.
An interesting study came from Australia (Truby, 2008). Again the population was adults 65 years and under. Four diet plans were assessed including the Atkins, Weight Watchers, Slim Fast and a local product. Although they only followed patients for two months, they found all diet groups lost significantly more weight than the control group. Differences were found in the levels of minerals and vitamins in patients. Slimfast showed a decrease in niacin and an increase in zinc in this older study.
An obvious conclusion is that bias may well have influenced this body of literature. The elderly are conspicuously absent from these studies. All studies involved calorie reductions for both groups. Weight loss was evident in almost all cases. The conundrum is the meta-analysis. We leave that to your assessment. We have validated our literature search with the assistance of a medical librarian. It is possible that we did not locate all relevant studies . Reported here is a summary of some of the best found for adults.
Ahrens, R. A., Hower, M., & Best, A. M. (2003). Effects of Weight Reduction Interventions by Community Pharmacists. Journal of the American Pharmacists Association, 43(5), 583-589.
Ashley, J. M. et al. (2007). Nutrient adequacy during weight loss interventions: A randomized study in women comparing the dietary intake tin a meal replacement group with a traditional food group. Nutrition Journal, 6, 12. doi: 10.1186/1475-2891-6-12
Davis, Coleman, et al. (2010). Efficacy of a meal replacement diet plan compared to a food-based diet plan after a period of weight loss and weight maintenance: a randomized controlled trial. Nutrition Journal 9:11.
Heymsfield (2003). Weight management using a meal replacement (PMR) strategy: meta and pooling analysis from six studies. International Journal of Obesity.
Noakes, Foster, et al.(2004). Meal replacements are as effective as structured weight-loss diets for treating obesity adults with features of metabolic syndrome. Journal of Nutrition. 134: 1894-1899. (AUSTRALIA)
Truby, Hiscutt, et al. (2008). Commercial weight loss diets meet nutrient requirements in free living adults over 8 weeks: a randomized controlled weight loss trial. Nutrition Journal, 7:25. (AUSTRALIA)
Kathy Russell-Babin, MSN, RN, ACNS-BC, NEA-BC
Sr. Manager, Institute for Evidence-Based Care
Meridian Health System