Article Index > Authors > Jeff S. Volek Ph.D., R.D.

It’s estimated that as many as 15% of adults use meal replacements as part of a strategy for losing weight. As the name implies, meal replacements or MRPs are nutritional supplements that can replace normal meals. They contain a blend of macronutrients—protein, fat and carbohydrates—and are available in a variety of forms including powdered mixes, bars and pre-made ready-to-drink shakes (RTDs).

MRPs are popular because, in addition to providing balanced nutrition, they’re easy to use, require minimal preparation, and most importantly, give structure to a daily eating plan.

Despite the popularity of MRPs, do they actually help people lose weight? According to several studies, that answer is a resounding yes!

MRPs help change behavior
In a long-term study assessing the role of MRPs in treating obesity, MRPs were shown to be a valid dietary strategy to treat obesity and aid in maintaining weight loss. ¹

In this study, which occurred over 5 years, overweight subjects who consumed an MRP 1-2 times daily lost about 10 pounds compared to a group of control subjects who gained about 15 pounds over the same period.

Experts generally attribute the success of MRPs to a change in behavior since for some people, the structure of having a prepared meal provides the needed motivation to reduce calories and lose weight. Furthermore, an MRP with a portion of its protein from a high quality protein source such as whey may have added weight loss benefits.

Whey helps maintain lean mass
Whey is a complex protein source loaded with essential amino acids (EAAs), which are indispensable for stimulating skeletal muscle protein synthesis and helping maintain lean body mass during dieting. Compared to other proteins, whey contains a higher proportion of EAAs, especially the branched-chain amino acids (BCAAs) leucine, isoleucine and valine, which have been shown to enhance body composition. Given the many benefits of whey protein, it could be hypothesized that a whey-casein MRP with whey as the first and primary ingredient would offer even greater weight loss benefits. A recent study confirmed this hypothesis.

MRPs reduce body fat
In a study of 38 overweight and sedentary male and female adults published in Nutrition and Metabolism , researchers looked at the effects of an MRP totaling 300 calories per serving (40g protein [from whey, casein and milk protein isolate], 25g carbohydrate, 6g fiber, vitamins and minerals). ² Subjects consumed this MRP once daily for 2 weeks and then twice daily for 8 more weeks. The MRP group also performed an exercise program consisting of both resistance exercise and endurance training 3 times per week.

The MRP-exercise group was compared to an exercise-only group as well as to a control group that did not participate in a diet or exercise plan. The groups were not given explicit instructions regarding caloric intake, thus this was a study that included minimal nutrition intervention.

Six pounds of fat lost, gained muscle
The most significant results were reflected in body composition. After 10 weeks, the MRP-exercise group experienced an average of 6 pounds of fat loss and a 2-pound increase in lean body mass. In comparison, the exercise-only group lost 2.4 pounds of fat and gained 1.8 pounds of lean body mass. The control group experienced minimal changes in body composition.

MRPs reduce cholesterol levels
Of the three groups, only the MRP-exercise group experienced a 12% reduction in cholesterol and a 13.3% reduction in LDL (“bad” cholesterol). This was likely due to lower carb intake levels and increased exercise.

Of the three groups, only the MRP-exercise group experienced a 12% reduction in cholesterol and a 13.3% reduction in LDL (“bad” cholesterol). This was likely due to lower carb intake levels and increased exercise.

MRPs improve exercise capacity
In addition to the improved body composition, the MRP-exercise group also showed significant improvement in several measures of exercise performance. Subects who consumed MRPs experienced a 6.2% improvement in VO2 max (maximal aerobic capacity) compared to only 4.5% in the exercise-only group.

In addition to the improved body composition, the MRP-exercise group also showed significant improvement in several measures of exercise performance. Subects who consumed MRPs experienced a 6.2% improvement in VO2 max (maximal aerobic capacity) compared to only 4.5% in the exercise-only group. In addition to the improved body composition, the MRP-exercise group also showed significant improvement in several measures of exercise performance. Subects who consumed MRPs experienced a 6.2% improvement in VO2 max (maximal aerobic capacity) compared to only 4.5% in the exercise-only group.

Also, the time to exhaustion during a standardized treadmill test improved by 21.2% in the MRP-exercise group compared to a 9.8% increase in the exercise-only group and a 1.4% increase in the control group.

High-protein MRP may be best
Siimilar to other studies, these findings support the various benefits of consuming MRPs. The above referenced study is unique, however, because it reports on other important health effects including greater fat loss, muscle gain, cardio-respiratory fitness responses to training and healthy cholesterol levels.

It’s unlikely traditional sugar-laden, high-carb MRPs sold in mass markets would be able to affect these measures in the same way. The MRP used in this study consisted of whey and other high quality milk proteins, fat as well as fiber and other micronutrients.

During the last 8 weeks of the study when the MRP-exercise group drank two MRPs a day, they increased their protein intake to 131g per day, increased fiber intake to 23g per day, lowered carb intake to 190g per day, lowered fat intake to 63g per day and consumed an average of 1,854 calories a day. Thus, the high-protein whey-based meal replacement had a positive overall impact on the nutrient composition of their daily diet, which is conducive for promoting robust health. If one were to consume a similar high protein (40g), low carb (25g), low fat (5g) MRP twice daily, one would expect to achieve the same results, when combined with exercise.

References
1. Keogh JB, Clifton PM. The role of meal replacements in obesity treatment. Obes Rev. 2005 Aug;6(3):229-34.
2. Lockwood CM, Moon JR, Tobkin SE, Walter AA, Smith AE, Dalbo VJ, Cramer JT, Stout JR. Minimal nutrition intervention with high-protein/low-carbohydrate and low-fat, nutrient-dense food supplement improves body composition and exercise benefits in overweight adults: A randomized controlled trial. Nutr Metab (Lond). 2008 Apr 21;5(1):11 [Epub ahead of print].