“People whose diets had a lower carbon footprint were eating less red meat and dairy — which contribute to a larger share of greenhouse gas emissions and are high in saturated fat — and consuming more healthy foods like poultry, whole grains, and plant-based proteins,” said lead author Diego Rose from the Tulane University in New Orleans.
For the study, published in the American Journal of Clinical Nutrition, researchers built an extensive database of the greenhouse gas emissions related to the production of foods and linked it to a large federal survey that asked people what they ate over a 24-hour period.
They ranked diets by the amount of greenhouse gas emissions per 1,000 calories consumed and divided them into five equal groups.
Then they rated the nutritional value of foods consumed in each diet using the US Healthy Eating Index, a federal measure of diet quality, and compared the lowest to the highest-impact groups on this and other measures.
Americans in the lowest carbon footprint group ate a healthier diet, as measured by this index. However, these diets also contained more of some low-emission items that aren’t healthy, namely added sugars and refined grains.
They also had lower amounts of important nutrients — such as iron, calcium, and vitamin D — likely because of the lower intakes of meat and dairy.
According to the researcher, overall, diets in the lowest impact group were healthier, but not on all measures. This is because diets are complex with many ingredients that each influence nutritional quality and environmental impacts.
Diets in the highest impact group accounted for five times the emissions of those in the lowest impact group. The highest impact diets had greater quantities of meat (beef, veal, pork and game), dairy and solid fats per 1000 calories than the low-impact diets.
“We can have both. We can have healthier diets and reduce our food-related emissions. And it doesn’t require the extreme of eliminating foods entirely,” Rose said.
“For example, if we reduce the amount of red meat in our diets, and replace it with other protein foods such as chicken, eggs, or beans, we could reduce our carbon footprint and improve our health at the same time.”