Press Release The University of Chicago


April 13, 2006


Study: vegan diets healthier for planet, people than meat diets

The food that people eat is just as important as what kind of cars

they drive when it comes to creating the greenhouse-gas emissions

that many scientists have linked to global warming, according to a

report accepted for publication in the April issue of the journal

Earth Interactions.


Both the burning of fossil fuels during food production and

non-carbon dioxide emissions associated with livestock and animal

waste contribute to the problem, the University of Chicago's Gidon

Eshel and Pamela Martin wrote in the report.


The average American diet requires the production of an extra ton and

a half of carbon dioxide-equivalent, in the form of actual carbon

dioxide as well as methane and other greenhouse gases compared to a

strictly vegetarian diet, according to Eshel and Martin. And with

Earth Day approaching on April 22, cutting down on just a few eggs or

hamburgers each week is an easy way to reduce greenhouse-gas

emissions, they said.


"We neither make a value judgment nor do we make a categorical

statement," said Eshel, an Assistant Professor in Geophysical

Sciences. "We say that however close you can be to a vegan diet and

further from the mean American diet, the better you are for the

planet. It doesn't have to be all the way to the extreme end of

vegan. If you simply cut down from two burgers a week to one, you've

already made a substantial difference."


The average American drives 8,322 miles by car annually, emitting 1.9

to 4.7 tons of carbon dioxide, depending on the vehicle model and

fuel efficiency. Meanwhile, Americans also consume an average of

3,774 calories of food each day.


In 2002, energy used for food production accounted for 17 percent of

all fossil fuel use in the United States. And the burning of these

fossil fuels emitted three-quarters of a ton of carbon dioxide per



That alone amounts to approximately one-third the average

greenhouse-gas emissions of personal transportation. But livestock

production and associated animal waste also emit greenhouse gases not

associated with fossil-fuel combustion, primarily methane and nitrous



"An example would be manure lagoons that are associated with

large-scale pork production," Eshel said. "Those emit a lot of

nitrous oxide into the atmosphere."


While methane and nitrous oxide are relatively rare compared with

carbon dioxide, they are - molecule for molecule - far more powerful

greenhouse gases than carbon dioxide. A single pound of methane, for

example, has the same greenhouse effect as approximately 50 pounds of

carbon dioxide.

In their study, Eshel and Martin compared the energy consumption and

greenhouse-gas emissions that underlie five diets: average American,

red meat, fish, poultry and vegetarian (including eggs and dairy),

all equaling 3,774 calories per day.


The vegetarian diet turned out to be the most energy-efficient,

followed by poultry and the average American diet. Fish and red meat

virtually tied as the least efficient.


The impact of producing fish came as the study's biggest surprise to

Martin, an Assistant Professor in Geophysical Sciences. "Fish can be

from one extreme to the other," Martin said. Sardines and anchovies

flourish near coastal areas and can be harvested with minimal energy

expenditure. But swordfish and other large predatory species required

energy-intensive long-distance voyages.

Martin and Eshel's research indicated that plant-based diets are

healthier for people as well as for the planet.


"The adverse effects of dietary animal fat intake on cardiovascular

diseases is by now well established. Similar effects are also seen

when meat, rather than fat, intake is considered," Martin and Eshel

wrote. "To our knowledge, there is currently no credible evidence

that plant-based diets actually undermine health; the balance of

available evidence suggests that plant-based diets are at the very

least just as safe as mixed ones, and most likely safer."


In their next phase of research, Eshel and Martin will examine the

energy expenditures associated with small organic farms, to see if

they offer a healthier planetary alternative to large agribusiness

companies. Such farms typically provide the vegetables sufficient to

support 200 to 300 families on plots of five to 10 acres.


"We're starting to investigate whether you can downscale food

production and be efficient that way," Martin said.



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