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"The take-home message is that health and environmental agendas are not aligned in the current dietary recommendations," says Martin Heller. (Credit: b3d_/Flickr)

agriculture

Diet guidelines could amp up greenhouse gas

If Americans followed the US Department of Agriculture’s “Dietary Guidelines for Americans, 2010” while keeping caloric intake constant, diet-related greenhouse gas emissions would increase 12 percent.

Researchers 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 the US Department of Agriculture.

If Americans reduced their daily caloric intake to the recommended level of about 2,000 calories while shifting to a healthier diet, greenhouse gas emissions would decrease by only one percent, according to coauthors Martin Heller and Gregory Keoleian of University of Michigan’s Center for Sustainable Systems.

“The take-home message is that health and environmental agendas are not aligned in the current dietary recommendations,” Heller says.

The paper’s findings are especially relevant now because the USDA Dietary Guidelines Advisory Committee is for the first time considering food sustainability within the context of dietary recommendations, he says.

Less meat, more dairy

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.

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The guidelines don’t explicitly state that Americans should eat less meat. However, an appendix to the report lists the recommended average daily intake amounts of various foods, including meat.

The recommended amount of meat is significantly less than current consumption levels, which Heller and Keoleian estimated using the USDA’s Loss Adjusted Food Availability dataset as a proxy for per capita food consumption in the United States.

While a drop in meat consumption would help cut diet-related greenhouse gas emissions, increased use of dairy products—and to a lesser extent seafood, fruits, and vegetables—would have the opposite effect, increasing diet-related emissions, according to the researchers.

In the United States in 2010, food production was responsible for about eight percent 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.

Hungry cows and their burps

The production of both beef cattle and dairy cows is tied to especially high levels of greenhouse gas emissions.

For starters, cows don’t efficiently convert plant-based feed into muscle or milk, so they must eat lots of food. Growing that food often involves the use of fertilizers and other substances manufactured through energy-intensive processes. And then there’s the fuel used by farm equipment.

In addition, cows burp lots of methane, and their manure also releases this potent greenhouse gas.

Greenhouse gas emissions associated with producing the US diet are dominated by the meats category, according to Heller and Keoleian. While beef accounts for only four percent by weight of the food available, it contributes 36 percent of the associated greenhouse gases, they conclude.

Go vegan?

The researchers found that a switch to diets that don’t contain animal products would lead to the biggest reductions in this country’s diet-related greenhouse emissions.

But Heller says he’s not arguing that all Americans should go vegan, and he believes that animals need to be part of a sustainable agricultural system. However, reduced consumption would have both health and environmental benefits.

In the paper, Heller and Keoleian also looked at wasted food and how it contributes to US greenhouse gas emissions. They conclude that annual emissions tied to uneaten food are equivalent to adding 33 million passenger vehicles to the nation’s roads.

Their paper appears today in the Journal of Industrial Ecology.

Source: University of Michigan

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