Portion Size Strategies for Management of Body Weight

The primary aim of this research is to determine the efficacy of two portion-control strategies to achieve sustainable dietary and behavior changes and to promote weight loss and maintenance. A randomized controlled trial will test two different approaches to managing portion sizes: one that gives individuals skills and tools to help them make appropriate portion choices, and another that focuses on consumption of pre-portioned foods in order to limit exposure to large portions in the personal food environment. During a 6-month intervention phase, 300 overweight and obese women will meet biweekly with dietitians for individual instruction; this will be followed by 6 months of monthly meetings to promote the maintenance of behavior changes and weight loss. Participants will be randomly assigned to one of three equally intensive intervention programs. All three groups will receive basic nutritional and behavioral intervention to promote weight loss. In addition, the portion-size instruction group will be given training in selecting portions and in the use of portion control tools such as measuring implements and charts. The instruction will include an innovative approach based on our previous research, which shows that consuming larger portions of foods that are low in energy density (such as vegetables and water- rich foods) enhances satiety and reduces energy intake. A second group of participants will be provided with pre-portioned foods (such as frozen entrées) for two meals daily at the beginning of the trial; the frequency of food provision will be reduced over the course of the intervention phase. Participants will be instructed in other methods for managing influences on food intake in their personal environment. The third group will receive the basic nutritional program supplemented with additional information on healthy eating during weight loss.

It is hypothesized that the two portion-control interventions will result in increased weight loss during the intervention phase, but that the maintenance of weight loss will depend on sustained changes in the acquisition and application of portion size knowledge. The second aim of the research is to determine the effects of the programs on knowledge and consumption of appropriate portions, as assessed by innovative assessment methods and multiple-pass dietary recalls. The third aim is to conduct exploratory analyses of individual factors that may influence the response to the portion-control interventions, such as psychosocial indicators, blood biomarkers, and measures of adherence to the interventions. The expected outcome of the project is that it will lead to the development of specific, evidence-based strategies to help control portion sizes in order to manage weight.