(P19-025-23) Macronutrient Composition of Plant-Based Diets and Breast Cancer Risk: The E3N Prospective Cohort Study

Objectives: Recent evidence supports the protective role of plant-based diets for breast cancer (BC). However, little is known about how the macronutrient composition of plant-based diets may help explain these associations. Therefore, we thought to explore the association of macronutrient composition with BC risk across a spectrum of plant-based diet indexes using a geometric framework approach.

Methods: A total of 64,655 participants from the Etude Epidémiologique auprès de femmes de la Mutuelle Générale de l'Education Nationale (E3N) cohort were followed from 1993 to 2014. Diet was assessed by validated FFQs at baseline (1993) and follow-up (2005) and adherence to the overall plant-based diet index (PDI), healthful plant-based diet (hPDI), and unhealthful plant-based diet (uPDI) was calculated. The association of macronutrient composition with BC risk was assessed via generalized additive models across different levels of these indexes. Response surfaces were generated to help visualize compositional associations at the 25^th, 50^th, and 75^th percentile of each index (low, moderate, and high respectively).

Results: A total of 3,932 BC incidents were identified across the 21-year follow-up. There was a significant association between macronutrient composition and BC risk for hPDI, uPDI, and PDI (P < 0.001 for all). For participants with a low hPDI score, the highest BC risk was observed for macronutrient profiles comprising 50% protein, 20% carbohydrate, 30% fat, or 15% protein, 70% carbohydrate, and 15% fat. Participants with moderate or high hPDI scores had overall lower BC risk but observed a region of higher risk with a moderate intake of all three macronutrients. For uPDI and PDI, participants with poor scores were overall at high risk, especially for diets composed of a combination of higher fat and higher protein for PDI, and a combination of higher carbohydrate and lower protein for uPDI.

Conclusions: These results demonstrate a complex relationship between dietary macronutrient composition, plant-based diet quality, and BC risk. Further research is needed to identify relevant foods that may be driving these associations.

Funding Sources: Ministère de l'enseignement supérieur de la recherche et de l'innovation