PLANETARY HEALTH DIET INDEX

Abstract

Food systems are one of the key driving factors of both human health and the environment. Agriculture and food production have been responsible for about 30% carbon footprint, 70% water footprint, and at least 40% land use over the past decade. In 2019, the EAT-Lancet Commission on Food, Planet, Health proposed a reference diet that can benefit both human health and planetary health. This dissertation included three studies regarding the development of a Planetary Health Diet Index (PHDI) to enable quantification of adherence to the EAT-Lancet dietary pattern and measuring the association of PHDI with both health and environmental impacts in the three prospective study in the United States (US). The first study of the dissertation presented the scoring criteria and the rationale for PHDI, then assessed associations between PHDI with total and cause-specific mortality in 66,692 females from the Nurses’ Health Study (1986-2019), 92,438 females from the Nurses’ Health Study II (1989-2019), and 47,274 males from the Health Professionals Follow-Up Study (1986-2018) who were free of cancer, diabetes, and major cardiovascular diseases at baseline. We found that in these three large US-based prospective cohorts of males and females with up to 34 years of follow-up, a higher PHDI was associated with lower risk of total and cause-specific mortality and diet-related environment impacts including greenhouse gas emission, crop land use, fertilizer use, and irrigation water. The second study of the dissertation evaluated the reproducibility and validity of the PHDI derived from food frequency questionnaires (FFQ) compared with the average of two 7-day dietary records (7DDRs). We included 652 males from the Men’s Lifestyle Validation Study (2011-2013) and 742 females from the Women’s Lifestyle Validation Study (2010-2012) who were free of cancer, and major cardiovascular/neurologic disease. Our analysis documented good reproducibility and validity of the FFQ for evaluating adherence to the PHDI. Correlations between the PHDI assessed by FFQ and circulating biomarkers support its biological relevance. After we calibrated the FFQ-derived PHDI to the weighed diet records, the observed associations between the PHDI and mortality in the three cohorts were slightly strengthened, and associations between the PHDI and environmental impacts were also stronger. The third study of the dissertation aimed to assess the association between the PHDI and disease burden measured by Disability-adjusted life years (DALY) in the Nurses’ Health Study (1986-2019). We followed 60,593 females who were free of cancer, diabetes, ischemic heart disease (IHD), stroke, chronic obstructive pulmonary disease (COPD), and Parkinson’s disease (PD) at baseline. We used the disability weights provided by Global Burden of Disease Study 2019 and the life expectancy from the US National Center for Health Statistics to calculate DALY. We found that in this large US-based prospective cohort of females, greater adherence to the planetary health diet was associated with lower burden of disease.