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Background Diets rich in fruits and vegetables (F/V) can reduce the inflammatory profile of circulating cytokines and potentially decrease the risk of breast cancer. However, the extent to which a diet rich in F/V alters cytokine levels in breast tissue remains largely unknown. Breast milk provides a means of assessing concentrations of secreted cytokines in the breast microenvironment and is a potential tool for studying the effects of diet on inflammation in breast tissue and breast cancer risk. Objective The aim of this pilot randomized trial was to test the feasibility of increasing F/V intake in breastfeeding women and of measuring changes in markers of inflammation in breast milk. Design and intervention Participants randomized to the intervention (n=5) were provided weekly boxes of F/V, along with dietary counseling, to increase consumption of F/V to 8 to 10 daily servings for 12 consecutive weeks. Controls (n=5) were directed to the US Department of Agriculture’s “ChooseMyPlate” diet for pregnancy and breastfeeding. Participants/setting Ten breastfeeding women consuming fewer than five servings of F/V per day, as estimated by the National Institutes of Health “All-Day” Fruit and Vegetable Screener (F/V Screener), were recruited through flyers and a lactation consultant between February and May 2016 in the Western Massachusetts area. Main outcome measures Baseline demographic and F/V intake data were collected during enrollment. At week 1 and week 13 (final) home visits, participants provided milk samples and anthropometric measurements were recorded. Participants completed F/V screeners at baseline and at study end. Adiponectin, leptin, C-reactive protein, and 11 additional cytokines were measured in breast milk collected at weeks 1 and 13. Statistical analyses F/V consumption at baseline and after the final visit, and between controls and intervention groups, was compared with dependent and independent t tests, respectively. Differences between cytokine levels at weeks 1 and 13 were assessed with a mixed-effects repeated-measures model. Results All women in the intervention increased F/V intake and were consuming more servings than controls by week 13; daily serving of F/V at baseline and final visit: controls=1.6 and 2.0, diet=2.6 and 9.9. Most cytokines were detected in the majority of milk samples: 12 were detected in 90% to 100% of samples, one was detected in 75% of samples, and one was detected in 7.5% of samples; coefficients of variation were below 14% for 11 of the cytokines. Conclusions These preliminary findings indicate that it is feasible to significantly increase F/V intake in breastfeeding women and provide support for conducting a larger diet intervention study in breastfeeding women, in which longer-term benefits of the intervention are assessed.