A structured diet and exercise program promotes favorable changes in weight loss, body composition, and weight maintenance

Journal Title (Medline/Pubmed accepted abbreviation): J. Am. Diet. Assoc.
Year: 2011
Volume: 111
Number: 6
Page numbers:828-843
doi (if applicable): 10.1016/j.jada.2011.03.013

Summary of background and research design

Background: It is common for weight loss programs to be evaluated independently for effectiveness, with many showing success. However, due to the difficulty of managing such a large sample size, it is less common to evaluate 2 different weight loss programs to see which is more effective than another.

Hypothesis: When comparing 2 weight loss plans, the one that has a more structured diet plan and supervised exercise would be more effective than a plan that includes ready-to-eat meal replacements and exercise recommendations.

Experimental design: randomized, comparative effectiveness trial

Subjects: Apparently healthy women, age 27-40 who had not recently been dieting or involved in exercise. In total, 90 people completed the 10 wk intervention study and 77 of the 90 completed the 24 week (6 mo) weight maintenance portion of the study following the 10 wk intervention.

Protocol: Women were first evaluated for their normal dietary and exercise practices as well as anthropometric measurements (height, weight, etc) and other health metrics (for example, blood pressure, muscular strength, and fasting blood glucose levels).  They were randomly assigned to follow 1 of 2 diets:

1) The Special K Challenge Program, which included replacing 2 meals per day with Special K cereal, 2/3 cup of skim milk, and fruit, where a third meal was eaten “as usual”.  Fruits and vegetables were encouraged as snacks.  After the first week, these participants were guided by a dietitian to reduce caloric intake by 500 kcal per week.  These participants were encouraged to increase physical activity and were educated on the types and durations of exercises that may be effective.

2)  The Curves diet program, which included a structured diet plan with 1200 kcal/day for the first week then 1600 kcal for weeks 2-10.  The macronutrient breakdown of these meals was 45% carbohydrates, 30% protein, and 25% fat.  Curves products (cereals and cereal bars) were built into this diet.  These people participated in a supervised Curves exercise program.  Exercise sessions were 3x/wk and included circuit-style workouts, alternating cardio and strength exercises, 30 sec per station. 

After 10 wks the participants were assessed again for body measurements and health metrics.  The participants were encouraged to follow a weight maintenance program for the 6 mos. following the intervention with educational information from professionals.
Summary of research findings
  • Total energy and fat intake decreased during the study compared to before, with no differences noted between groups.
  • The supervised exercise group engaged in more exercise than the meal replacement group.  Moreover, during the 24 wk weight maintenance group, those in the supervised exercise group maintained higher amounts of exercise than the meal replacement group.
  • The supervised exercise group lost more weight (3.1 ± 3.7 kg vs. 1.6 ± 2.5 kg), fat mass, and centimeters from the hip and waist than the meal replacement group at 10 weeks {NOTE:  in Table 5 of the article, the 10-wk weight loss for the structured exercise group appeared to be 3.3 kg, in contrast to the 3.1 kg reported in the abstract}.  Those in this group also showed greater aerobic capacity and strength after the intervention.
  • At a 34-week follow-up visit during the weight maintenance phase, the mean weight loss for the structured diet and exercise group was 3.1 kg, as opposed to 2.2 kg in the meal replacement group (group effect P<0.05).  Thus, it appeared that maintenance of weight loss was better in the structured diet and exercise group as well.

Interpretation of findings/Key practice applications

Both weight loss programs were effective: replacing meals with portion-controlled, low calorie meals can help achieve negative energy balance and a structured diet and exercise plan was effective for weight loss. The participants in the supervised exercise program engaged in more physical activity than the meal replacement group despite both groups being educated on proper physical activity. This explains why the supervised exercise group to lose twice as much weight as the other group. For those struggling with weight loss, a structured exercise program might be worth a try.


Before the authors started the study, they specified that compliance for the supervised exercise program would be defined as attendance at 80% of the 102 scheduled exercise sessions. However, they did not report how many participants did not comply with the exercise sessions. It is not clear what was done with the data from those who did not attend at least 80% of the sessions. Further, the authors did not provide the rate of the compliance measured for the meal replacement group. (It was reported that 87% of the participants overall were compliant in the initial 10 wk intervention.) It would have been interesting to see how exercise and diet compliance rates differed between the two groups.

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