Dietary Intervention Methods for Clinical Trials

BACKGROUND:

A study by the investigators showed that a method based on principles of antecedent control, namely the provision of food to participants, was successful in almost doubling weight losses over a twelve month period compared to those attained in a standard behavioral weight control program. These weight losses were associated with substantial improvements in cardiovascular risk factors.

DESIGN NARRATIVE:

There were several studies in this two-center project (R01HL41330 and R01HL41332). Obese subjects, male and female, were recruited at the University of Pittsburgh and the University of Minnesota. The subjects were randomly assigned to one of five treatment groups: no treatment control, standard behavioral nutrition program, standard program with incentives, standard program with food provision, and standard program with both incentives and food provision. The effectiveness of the treatments was analyzed by assessing changes in body weight, coronary heart disease risk factors (lipids, blood pressure, insulin, and glucose) and process variables (eating and exercise behavior, knowledge, barriers to adherence) at six month intervals for eighteen months.

The project was renewed in April 1992 and included four studies. Study 1 determined whether there were long-term benefits to food provision by reexamining the 202 participants in the original study one year after the end of treatment. Study 2 investigated the factors related to the successful food provision intervention by comparing the additive effects of standard behavioral treatment and the three central components of food provision: structured meal plans, prepackaged food and subsidy of the food. It also explored theoretical mechanisms which might underlie the food provision effect, specifically decision making and stimulus control. Study 3 evaluated the effectiveness of extending the food provision methodology to families. Overweight spouse pairs were randomized to treatments in which either one member of the pair participated in treatment and received food, or both members of the pair participated and were provided with food. Study 4 determined whether the principles of antecedent control could also be applied to exercise. Participants were randomized to weight control programs which included either the usual exercise instructions or structured plans for exercise and free passes to exercise facilities near their home. It was hypothesized that providing food for the obese spouse as well as the patient, and providing antecedent control for exercise through structured plans and free passes would both improve the maintenance of weight loss.

The studies were renewed in FY 1998 through April, 2002 to compare the long-term weight losses achieved in a standard behavioral program with those obtained in an enhanced exercise intervention. The exercise goal in the standard program was 1000 kcal/week, while that in the enhanced exercise program was 2500 kcal/week. The study was conducted with 180 subjects divided equally between men and women, half recruited in Minneapolis and the other half in Pittsburgh. The primary hypotheses were that the enhanced exercise intervention group would have significantly greater weight losses than the standard intervention group at the end of the 18 month treatment program and at the 30-month follow-up. In addition, the two conditions were compared at 0, 6, 12, 18, and 30 months with regard to exercise levels, variables that might be related to exercise and weight loss, and measures related to quality of life. Furthermore, the investigators attempted to determine predictors of long-term weight loss and exercise behavior, and examined the effects of social support on exercise level and weight loss of the enhanced exercise intervention group.

Include both R01HL41330 and R01HL41332.