Background: Cohort studies suggest that higher circulating carotenoid concentrations through food sources may reduce breast cancer events. Other intervention studies have not achieved the level of change in circulating carotenoids required to properly test this hypothesis. Methods: In a randomized trial of 2,922 breast cancer survivors, we examined blood and self-reported diet at baseline and 1 year. Intensive telephone counseling encouraged a plant-based diet in the intervention group. Diet was measured via 24-hour recalls, and a panel of plasma carotenoid concentrations was assessed at both time points. Results: The study intervention was associated with a 51% increase in total carotenoid concentration, from 2.272 ±1.294 to 3.440 ± 2.320 μmol/L, achieved mainly by marked increases in targeted carotenoids: α-carotene, β-carotene, and lutein. For each of these targeted carotenoids, the proportion of the intervention sample remaining below the cutpoint for the lowest baseline quartile decreased by one third to one half. After 1 year of study, half of the intervention group was in the highest baseline quartile. No change in distribution was observed in comparison group. Intervention participants achieved this change by both dietary pattern and vegetable juice consumption. Participants who chose to change dietary pattern without consuming significant quantities of vegetable juice achieved 75% of the level of change observed in other intervention participants. Conclusions: Innovative telephone counseling intervention and dietary targets in the Women's Healthy Eating and Living study were associated with the level of change in circulating carotenoid concentration necessary to test the diet and breast cancer hypothesis suggested by cohort studies.
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