Abstract

Background Dietary choices affect both health and the environment. Few studies, and none in the USA, have examined these links at the individual level, limiting our ability to describe the variation in response to environmentally focused food policies. To address this gap, our study aimed to examine the relation between healthiness and environmental effects of individual diets in the USA.

Methods We examined 24-h dietary recalls from a nationally representative sample of US adults (n=13 203), aged 18–65 years, in the 2005–10 National Health and Nutrition Examination Survey. We converted reported food intakes to commodities using resources from the US Environmental Protection Agency, and matched these to a database of greenhouse gas emissions (GHGE) in carbon dioxide equivalents, which we developed from a comprehensive review of life cycle assessment studies. In addition to calculation of the GHGE per 1000 kilocalories per day for each individual, we assessed the healthiness of their diets using the Healthy Eating Index (HEI), a 12-component score ranging from 0 to 100, developed by the US Department of Agriculture and the National Cancer Institute.

Findings GHGE from food were inversely related to the HEI; those in the lowest quintile of emissions had HEI scores 3·2 points higher (95% CI 2·0–4·4) than those in the highest quintile. On average, a 10% decrease in emissions was associated with a 0·4% (95% CI 0·2–0·6) increase in HEI. These results were similar after controlling for sex and ethnicity or when using a subsample of individuals describing their intake amount as usual.

Interpretation This is the first nationally representative dietary study of the environmental effects of US individuals. Because higher healthy eating scores were associated with lower greenhouse gas emissions in these self-selected diets, our results suggest that objectives to improve nutritional health and lower environmental effects in the USA are compatible. This also strengthens arguments to include sustainability considerations in dietary guidance policies.