Press Release
The University of Chicago
April 13,
2006
http://www-news.uchicago.edu/releases/06/060413.diet.shtml
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
person.
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
oxide.
"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.