It’s been a tough couple of years for the public relations staff in the biofuels industry.

The production of biofuels from crops like corn has been blamed for everything from driving up global food prices and deforestation in the Amazon to depleting oxygen in the Gulf of Mexico (not to mention raising the price of tequila).

Even the basic purpose of today’s commercial biofuels production has been called into question.

A study by researchers at the University of Minnesota, published in 2008 in the journal Science, found that if previously undeveloped landscapes are cleared for biofuels production, then those biofuels emit more greenhouse gases than gasoline and diesel. Policymakers and the public are now asking if it’s efficient or ethical to use croplands to feed machines rather than people.

There’s one obvious place to look for an answer. In North America, we have been feeding the majority of our crops to machines for decades. These elaborate, protein-producing devices are best known by their common names: cows, pigs and chickens.

Eating animals is hardly new. Our nomadic hunter-gatherer ancestors relied on meat for a large proportion of their protein intake. But the advent of agriculture and rise in population after the end of the last ice age led humans to settle in villages and shift to a more energy-efficient, grain-based diet. Over time, meat would be reserved for those who could afford the land and workforce required to raise animals.

Diets in the developed world changed again with the discovery of fossil fuels, especially oil. This cheap source of energy allowed us to produce nitrogen fertilizers, transform crop genetics, fuel agricultural machinery and transport agricultural products around the world. Buoyed by high crop yields and newfound agricultural wealth, we began feeding large quantities of grain and oilseeds to our farm animals.

Today, the average American eats as much as 275 pounds of meat each year, up from 197 pounds in the early 1960s.

Feeding the literally billions of cattle, poultry and pigs now requires a large proportion of the world’s—and mainly America’s—croplands. More than two-thirds of the American corn, soybean, sorghum, barley and oats harvest is used to produce animal feed. That’s more than two-thirds of the fuel used to operate machinery, more than two-thirds of the agricultural chemical use and subsequent water pollution, and more than two-thirds of greenhouse gas emissions from croplands.

In the coming decades, the demand for both animal feed and transportation fuels is expected to rise sharply as Asia and the developing world become wealthier. According to the Food and Agriculture Organization of the United Nations, per capita meat consumption in China has doubled since 1990, and it could double again.

Can our agricultural system meet this increasing demand while also reducing greenhouse gas emissions, tropical deforestation and water pollution? The solution may be switching to more efficient machines.

Like the cars we drive, the animals we eat have wide-ranging efficiencies. Beef cattle are the SUVs of animal agriculture. Renowned energy expert Vaclav Smil calculated that the U.S. agricultural system uses 32 kilograms of feed to produce 1 kilogram of edible beef. Poultry is the fuel-efficient compact of the animal world, with around one-eighth the feed ratio of beef.

The good news is that Americans have been slowly shifting their diets from beef toward more efficient forms of food production. Since the 1970s, per capita beef consumption has decreased 20 percent, while per capita poultry consumption increased by 40 percent. And more and more Americans are forsaking beef or all meat out of health concerns.

A more aggressive move toward poultry, dairy and vegetable-based diets could greatly decrease the land, energy and fertilizer needed to feed the population. In turn, this change would decrease direct greenhouse gas emissions from food cultivation and nutrient pollution to waterways. My own research indicates that reducing beef consumption in American diets would also reduce nitrogen pollution in the Mississippi River and shrink the dead zone in the Gulf of Mexico.

Changing diets would also free up productive croplands for cultivating second-generation biofuels based on unfertilized grains, oil crops or grasses. This newly available land would help eliminate concerns that diverting productive croplands to biofuels cultivation causes the clearing of native vegetation and the release of stored carbon elsewhere in the world.

In a carbon-constrained world, food efficiency may be just as important as fuel efficiency. View Ensia homepage

This Voice originally appeared in the Winter 2009 issue of Momentum magazine as “Fueling the Future.”