Lower carbon diets best for planet

A STUDY examining the carbon footprint of what more than 16 000 Americans eat in a day has good news for environmentally conscious consumers – diets that are more climate-friendly are also healthier.

The research by Tulane University, which is published in the American Journal of Clinical Nutrition, is the first to compare the climate impact and nutritional value of diets using real-world data.

“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 healthful foods like poultry, whole grains and plant-based proteins,” said lead author Diego Rose, a professor of nutrition and food security at the university’s School of Public Health and Tropical Medicine.

As food production is a major contributor to climate change, researchers from Tulane and the University of Michigan sought to learn more about the impacts of Americans’ daily dietary choices. They built an extensive database of the greenhouse gas emissions related to the food production and linked it to a large federal survey that asked people what they ate over a 24-hour period.

Researchers ranked diets by the amount of greenhouse gas emissions

People whose diets had a lower carbon footprint were eating less red meat and dairy

Diego Rose

per 1 000 calories consumed and divided them into five equal groups.

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 with 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, the diets also contained more of some low-emission items that aren’t healthy – added sugars and refined grains.

They also had lower amounts of iron, calcium, and vitamin D, probably because of the lower intakes of meat and dairy. Overall, diets in the lowest impact group were healthier, but not on all measures.

Rose says this is because diets are complex with many ingredients that each influence nutritional quality and environmental impacts. “This explains the nuanced relationship we observed between these outcomes,” he said.

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, dairy and solid fats per 1 000 calories than the low-impact diets.

Overall, the high-impact diets were more concentrated in total proteins and animal protein foods.

A companion study the researchers released earlier this year found that 20% of Americans accounted for almost half of US diet-related greenhouse gas emissions.

Rose hopes the research will help the public and policymakers recognise that improving diet quality can also help the environment. “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. For example, if we reduce the amount of red meat 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.”

Professor of nutrition at Tulane University’s School of Public Health and Tropical Medicine