The climate footprint of what people eat changes across the lifespan, but a new study suggests those differences cannot be explained by individual food choices alone.
After analyzing dietary patterns across 149 countries, researchers found that adolescents and young adults had the highest food-related greenhouse gas emissions per person. Adults 60 and older, meanwhile, accounted for a growing share of total dietary emissions, largely because older populations are increasing in size rather than because older adults eat especially emissions-intensive diets.
The findings, published in Nature Food, complicate attempts to identify a single age group as most responsible for the environmental effects of food. They also highlight a difficult tension: Some dietary changes that increase emissions may improve nutrition, particularly in lower- and middle-income countries where people are gaining access to a wider range of foods.
Researchers examined food consumption and dietary emissions across 22 age groups from 2000 through 2019. The analysis covered 141 food products and combined dietary surveys, global food consumption estimates, population data and greenhouse gas emission inventories.
This was a population-level statistical analysis, not a study that directly tracked the diets of individual participants. The findings describe broad patterns across countries and age groups, so they cannot show that a person’s age causes them to choose a more emissions-intensive diet.
Globally, adolescents ages 11 to 19 and young adults ages 20 to 29 had the highest estimated dietary emissions per person. Researchers linked that pattern partly to greater consumption of meat, dairy products, sugary foods and drinks.
Those broad age categories include people living under vastly different economic, cultural and nutritional circumstances, however. The factors shaping a teenager’s diet in a high-income country may bear little resemblance to those affecting someone of the same age in a country where food access and undernutrition remain serious concerns.
Dietary emissions also do not necessarily move in the same direction as nutritional quality.
In some emerging economies, rising incomes have allowed people to eat more food and add products that may provide important nutrients. Those shifts can improve dietary quality while also increasing emissions.
“In many low- and middle-income countries, dietary shifts towards certain nutrient-rich foods have improved nutritional quality, but have also contributed to rising emissions,” study co-author Klaus Hubacek said. “This means that simply reducing certain types of food may have unintended health effects.”
The study identified meat consumption, particularly red meat, as a major contributor to growth in dietary emissions. Dairy products also played an important role, although the patterns differed among countries.
In China, researchers linked much of the increase in dietary emissions to greater meat consumption. In India, a shift toward more dairy products was a substantial contributor.
Those examples underscore why dietary sustainability cannot be reduced to one universal list of foods everyone should eat more or less often. The nutritional importance, accessibility and cultural role of a food can vary substantially among populations.
The analysis also found that dietary emissions increased globally by an estimated 2.1 gigatons of carbon dioxide equivalent between 2000 and 2019. Adults 60 and older accounted for 25.4% of that increase, the largest share attributed to any age group.
That does not mean older adults had the most emissions-intensive individual diets. Much of their growing contribution came from demographic change: People are living longer, birth rates are falling in many countries and older adults now make up a greater share of the population.
In high-income countries, adults 60 and older accounted for an estimated 22% to 29% of total dietary emissions. Their individual diets were not necessarily becoming more carbon-intensive. There were simply more older adults contributing to the overall total.
The distinction between per-person emissions and total population emissions is central to understanding the results. Younger people had the highest estimated dietary footprint per person, while older adults’ share grew most rapidly because of population aging.
The findings do not support blaming either group. Younger people often have limited control over the foods available at home, at school, at work or in their communities. Older adults have changing nutritional requirements and may face health conditions, mobility limitations or food-access challenges that shape what they can eat.
The researchers argue that strategies to reduce dietary emissions should account for those different circumstances.
For children, adolescents and young adults, that could involve improving school meals and other food environments rather than placing responsibility solely on individual choices. For older adults, the priority may be ensuring that lower-emission diets still provide enough protein, energy and essential nutrients to support health as people age.
Policies in lower- and middle-income countries may need to balance environmental goals with the continuing need to improve food security and nutritional adequacy. Changes that look beneficial from an emissions standpoint could be harmful if they limit access to foods that help address undernutrition or nutrient deficiencies.
The study also points beyond individual diets to food production. Reducing the emissions associated with producing and distributing foods could lower their climate impact without requiring people to remove nutritionally important foods from their diets.
The research received support from the New Chongqing YC Project through the Chongqing Municipal Bureau of Science and Technology, the Chongqing University Hongshen Start-up Grant, the China Scholarship Council PhD Program, UK Research and Innovation, the European Union’s Horizon Europe research and innovation program and the European Research Council.