Low-Carbon Diets Are Good for the Planet, and Your Health

For most of human history, sticking to a diet was pretty simple—you ate whatever you could get your hands on. But in this era of dietary excess, things have gotten extremely complicated. Conscious consumers need to consider the health implications of the foods they eat as well as the types of chemicals used in their production, the exploitation of farm labor, whether food animals are treated humanely, and just how much damage their afternoon snack is doing to the climate. Untangling the web of food choices is daunting, but a new study makes things a little bit easier. A paper in the American Journal of Clinical Nutrition shows that low-carbon diets that are good for the climate are, as a general rule, much better for human health as well.

Any discussion of climate change needs to address the world’s food system, which, by the latest measures, contributes up to 30 percent of all greenhouse gases. But guidance on how consumers can make sustainable choices is less clear. In a 2015 report, the Dietary Guidelines Advisory Committee, which comes up with government-recommended guidelines every five years, suggested environmental sustainability should be part of the 2015–2020 recommendations. But after an outcry by members of Congress and many agriculture producers, any mention of sustainability was nixed. 

The controversy, though, energized researchers to take a closer look at the relationship between climate and diet, says coauthor Martin Heller of the University of Michigan Center for Sustainable Systems. The latest study is a follow-up to another released earlier this year in Environmental Research Letters finding that just 20 percent of Americans were responsible for 50 percent of all food-related greenhouse gas emissions. “A lot of motivation here is to build further evidence on that and provide a basis for more nuanced work on policy direction and behavioral change in the US.”

To understand more about US diets and their climate impact, the team relied on the National Health and Nutrition Examination Survey, which collected a one-day snapshot of what a wide cross section of 16,000 Americans ate over a 24-hour period. The team then linked those diet diaries with a large database of the greenhouse gas impact of food items, determining the average carbon footprint and ranking the diets in five groups based on the climate impact per 1,000 calories consumed. They also assessed the diets using the US Healthy Eating Index, a federal guideline ranking a diet’s quality on a scale of one to 100.  

The team found that the better a diet was for the planet, the better it was for human health. That’s because the most climate-friendly diets eat fewer animal products, which are main drivers of carbon emissions and also have a negative impact on the Healthy Eating Index. 

“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,” lead author Diego Rose of Tulane University’s School of Public Health and Tropical Medicine said in a statement.

That’s not to say the low-emission diets were perfect. In many cases, they contained too many products that aren’t necessarily healthy, like refined flour and excess sugars, but have relatively low carbon footprints. And some climate-friendly menus lacked enough vitamin D, calcium, and iron. Overall, there’s a lot of room for improvement in the health and carbon footprint of the average American diet, which now averages 59 out of 100 on the Healthy Eating Index. 

Last week, another major report from the EAT-Lancet Commission recommended the same thing but on a global scale. Besides driving deforestation, climate change, malnutrition, and obesity, the report points out, the way humanity currently eats will make it impossible to feed the estimated 10 billion people who will live on Earth by 2050. The report goes so far as to recommend a “planetary health diet,” which relies heavily on whole grains, vegetables, legumes, and nuts, with red meat reduced to one serving per week, if that. 

There has been the expected pushback from the agricultural industry against the report, and some nutritionists say such a diet needs to be tailored to different parts of the world, which face different problems in their food systems. 

Still, both studies underline the point that climate change and sustainability will have to be addressed via the food system sooner or later. Heller says that the idea is starting to gain traction. “It feels like these notions are starting to come up in higher-level conversations about climate action and at climate summits. I think it’s timely. We need to push on the behavior change piece, and shifts are challenging, like changing meat consumption in the US,” Heller says. “It’s a transition that needs to happen, and I think it will happen with time.”