Abstract
OBJECTIVE: Effective dietary intervention strategies that can be widely disseminated and have the potential for sustainable dietary modifications are needed. The purpose of this study was to describe and evaluate the effectiveness of a telephone-based soy intervention. DESIGN: A randomized controlled trial comparing self-reported intake and serum measures of soy during a 1-year dietary soy (Soy) to fruit and vegetable (Placebo) intervention conducted in two of five arms from the Herbal Alternatives Trial between May 2001 and September 2004. SUBJECTS/SETTING: One hundred sixty-three peri- and postmenopausal women (mean age=52 years) consuming self-selected diets in the Pacific Northwest, United States. INTERVENTION: Five telephone contacts with a registered dietitian during a 12-month intervention with the goal to increase soy food consumption to two servings daily. MAIN OUTCOME MEASURES: Change from baseline in self-reported soy servings and serum isoflavone (daidzein and genistein) concentrations were estimated using analysis of variance and generalized estimating equations. Proportions of participants achieving the intervention goal were compared using chi(2) tests. RESULTS: Ninety-four percent (n=74) of participants in the Soy arm and 89% (n=75) in the Placebo arm completed the trial, and slightly more than one third (n=27) received five phone contacts. Mean (+/-standard deviation) intakes of soy were similar for the Soy and Placebo arms at baseline (0.6+/-1.0 vs 0.4+/-0.8 servings/day; P>0.05). At 12-month follow-up visit, mean+/-standard deviation servings of soy per day were 1.6+/-1.4 for the Soy intervention compared to 0.5+/-0.9 within the Placebo arm (P<0.001). There were concomitant increases in serum isoflavones at 3 and 6 months from baseline in the Soy arm only, with approximately twofold increases in both daidzein (mean=66.4 nmol/L, 95% confidence interval [CI]: 39.0 to 93.9 [mean 16.9 ng/mL, 95% CI: 9.9 to 23.8]) and genistein (mean=100.4 nmol/L, 95% CI: 60.9 to 139.9 [mean 27.1 ng/mL, 95% CI: 16.5 to 37.8]) concentrations. Mean weight changed by <1 kg during the 12-month period in each group and physical activity remained stable, suggesting that participants incorporated soy foods into their diet by substituting for non soy foods rather than adding them to their diet. CONCLUSIONS: A brief telephone-based intervention with a focused message delivered by a registered dietitian is a feasible approach for encouraging targeted dietary changes, such as an increase in soy intake among peri- and postmenopausal women.