Diet-related greenhouse gas emissions could increase by as much as 12% if Americans adhered to the USDA's 2010 Dietary Guidelines and caloric intake remained constant, a pair of University of Michigan researchers say.
Martin Heller and Gregory Keoleian of U-M's Center for Sustainable Systems looked at the greenhouse gas emissions associated with the production of about 100 foods, as well as the potential effects of shifting Americans to a diet recommended by USDA.
The researchers found that if caloric intake was adjusted to the recommended level of about 2,000 calories while adhering to the USDA guidelines, GHG emissions would decrease by only 1%.
The paper titled "Greenhouse gas emission estimates of U.S. dietary choices and food loss" detailing the findings was published Friday in the Journal of Industrial Ecology.
"The take-home message is that health and environmental agendas are not aligned in the current dietary recommendations," Heller said.
The paper's findings come as the USDA Dietary Guidelines Advisory Committee works to revise the guidelines while considering food sustainability within the context of dietary recommendations.
In its 2010 dietary guidelines, USDA recommends that Americans eat more fruits, vegetables, whole grains, fat-free and low-fat dairy products, and seafood. They should consume less salt, saturated fat, trans fat, cholesterol, added sugar and refined grains.
What about meat? >>
An appendix to the report lists the recommended average daily intake amounts of various foods, including meat, which is recommended at lower than current consumption levels estimated by the researchers.
While a drop in meat consumption would help cut diet-related greenhouse gas emissions, the researchers found that increased use of dairy products—and to a lesser extent seafood, fruits and vegetables—would have the opposite effect, increasing diet-related emissions.
In the United States in 2010, food production was responsible for about 8% of the nation's greenhouse gas emissions. In general, animal-based foods are responsible for more greenhouse gas emissions per pound than plant-based foods, U-M says.
U-M says cows especially don't efficiently convert plant-based feed into muscle or milk, so they must eat lots of feed. A university statement suggests that growing the feed for cows "often involves the use of fertilizers and other substances manufactured through energy-intensive processes."
The statement also cites fuel burned by farm equipment and methane emitted by cows that contributes to GHG emissions.
While beef accounts for only 4% by weight of the food available, according to Heller and Keoleian. it contributes 36% of the associated greenhouse gases.
The U-M researchers suggest that switch to diets that don't contain animal products would lead to the biggest reductions in this country's diet-related greenhouse emissions, but that doesn't mean all Americans should go vegan, Heller believes, and animals need to be part of a sustainable agricultural system.
In the researcher's paper, Heller and Keoleian also looked at wasted food and how it contributes to U.S. greenhouse gas emissions. They concluded that annual emissions tied to uneaten food are equivalent to adding 33 million passenger vehicles to the nation's roads.