Planetary Health Diet Index and breast cancer risk.

BACKGROUND

In 2019, the EAT-Lancet commission defined a "planetary health diet", a combination of food groups and ranges of food intakes that would simultaneously optimize human health and environmental sustainability. We aimed to evaluate adherence to the Planetary Health Diet Index (PHDI) and breast cancer incidence.

METHODS

We followed 68,254 participants in the Nurses' Health Study (NHS; 1986-2018) and 93,283 in the Nurses' Health Study II (NHSII; 1991-2019). The PHDI was calculated every 4 y using a validated, semiquantitative food frequency questionnaire. Hazard ratios (HRs) were calculated using multivariable proportional-hazards models.

RESULTS

During 4,182,897 person-years of follow-up, we documented 10,378 invasive breast cancer cases. Women in the highest, compared to lowest, PHDI quintile (Q) were at lower breast cancer risk (HRQ5 vs. Q1 = 0.89; 95% CI: 0.84, 0.95; P-trend<0.01) even after adjusting for weight change. Although heterogeneity by estrogen receptor (ER) status was nonsignificant, the strongest association was observed for estrogen receptor (ER) negative tumors (HRQ5 vs. Q1 = 0.79; 95% CI: 0.66, 0.93; P-trend = 0.01).

CONCLUSIONS

Adhering to a diet that supports both human and planetary health was associated with lower breast cancer risk, particularly ER-negative tumors. Strategies to reduce breast cancer incidence should emphasize the win-win opportunities for a high planetary health diet.