Diet quality and environmental sustainability: integrating dietary indices and planetary impacts

Abstract

Dietary patterns are major determinants of nutritional status and environmental sustainability. Despite growing interest in sustainable diets, limited research has examined how dietary carbon footprints differ across age groups and how age-specific dietary behaviors interact with diet quality to shape environmental impact. To assess dietary carbon footprints across age groups and determine how differences in food consumption patterns contribute to variation in CO 2 -equivalent emissions, while examining the relationship between diet quality and environmental impact across the lifespan to identify age-specific contributors to dietary emissions. This observational, descriptive study estimated diet-related CO 2 -equivalent emissions from dietary intake data obtained from 653 food frequency questionnaires (FFQs) collected from children assessed at 6, 12, 24, 36, and 48 months ( n = 114, 110, 93, 85, and 45, respectively; 54.4–62.2% male) and adults aged 18–50, 51–65, and 66–95 years ( n = 21, 102 and 83, respectively; 32.4–33.3% male). Demographic, lifestyle, anthropometric, and dietary intake data were collected, and CO 2 -equivalent emissions per kilogram of food consumed and dietary indices were calculated. Dietary CO 2 -equivalent emissions varied across age and BMI groups and were strongly associated with dietary composition. Animal-source foods, particularly meat and dairy, were the main contributors. Younger adults had the highest emissions, associated with greater consumption of red and processed meat and ultra-processed foods, whereas older adults showed more plant-based dietary patterns associated with lower emissions. Diet quality indices differed in their ability to capture environmentally sustainable dietary patterns, with the Planetary Health Diet Index (PHDI) and American Cancer Society 2020 (ACS-2020) dietary index, showing the strongest inverse associations with emissions. These findings highlight the importance of promoting plant-rich, minimally processed dietary patterns across the lifespan to support both human health and environmental sustainability.