Just to be clear, we do eat a little bit of grass. Three-quarters of all human nutrition comes from wheat, rice and corn, all of which are grasses. But what we eat is actually their seeds, the dense package of complex carbohydrates that is the specialty of annual grasses. Perennial grasses, which are more common, pack a larger proportion of their energy in their roots, stems and leaves; the building block for these is cellulose. Humans cannot convert cellulose to protein, but cows, sheep and other ruminants can, thanks to the resident bacteria in their highly specialized fermentation tank of a stomach, known as a rumen.

Most of the beef sold in stores today is from animals that are grain-fed, meaning they were fed corn and other grains over their lifetime, typically in a confined feedlot. Grass-fed beef, as its name implies, comes from animals that eat perennial grasses all their lives.

So what’s the big deal? Why is it so important to choose grass-fed when buying meat?

1. Perennial grasses are better for soil.

Healthy topsoil is a biological matrix, a housing complex for an incredibly diverse community of organisms. In every handful are billions of beneficial microbes, nitrogen-fixing fungi, nutrients and earthworms whose digestive tracts transform fine grains of sterile rock and plant detritus into the fertile excrement that gave rise to the word dirt itself (drit in Old Norse).

In his book "Dirt, David Montgomery, a geomorphologist at the University of Washington, describes modern agricultural practices as "soil mining" to emphasize that we are using up topsoil much more quickly than Earth's natural processes can restore it. According to the National Academy of Sciences, cropland in the United States is being eroded at least 10 times faster than the rate at which lost soil can be replaced by natural processes. Tillage, by moving topsoil with high levels of organic matter into the moist depressions, releases not only carbon dioxide but also nitrous oxide and methane (both global-warming gases) by triggering decay and erosion. Shallow-rooted annual grasses, such as corn, wheat and soy, further deplete the soil of critical trace minerals such as calcium, magnesium and iodine.

In contrast, the deep roots of perennials, often extending more than 10 feet below the surface, act like elevators, lifting nutrients back into the system and making them available to plants and everything else up the food chain. Pure prairie builds up organic matter: the richest of virgin prairie soil in the Midwest once ran to 10 feet deep and was about 10 percent organic. What's left of the soils where corn and soy now grow typically contains less than half that amount of organic matter. Perennial pastures can restore the richness of the soil in a decade or so.

2. Animals that are grass-fed their entire life are healthier — and their meat is safer for you.

A ruminant’s gut is normally a pH-neutral environment, best suited to a diet of cellulosic grasses. It is not well suited to a diet of corn and other grains, the primary fare of feedlot cattle. High in starch, low in roughage and a poor source of calcium and magnesium, corn upsets the cow’s stomach, making it unnaturally acidic. Not only is this harmful to the cow — giving it a sort of bovine heartburn or, worse, making it very sick—but it allows a whole range of parasites and diseases to gain a foothold, including the pathogenic E. coli 0157:H7 bacterium.

Making its first appearance a little over 25 years ago, E. coli is now found in the intestines of most U.S. feedlot cattle. As Michael Pollan explained in "Power Steer," a 2002 New York Times Magazine article, "By acidifying a cow's gut with corn, we have broken down one of our food chain's barriers to infections."

Interestingly, this process can be reversed, according to a U.S. Department of Agriculture microbiologist, who discovered that switching a cow's diet from corn to hay in the final days before slaughter reduces the population of E. coli in its manure by as much as 70 percent. Such a change, however, is considered wildly impractical by the cattle industry (see 4 below for reasons).

3. Grass-fed animals produce the right kind of fat.

Many of us think of corn-fed beef as being nutritionally superior, but it isn't. A corn-fed cow does develop well-marbled flesh, and the USDA continues to grade beef in a way that rewards marbling with intramuscular fat, but this is simply saturated fat that can't be trimmed off.

Grass-fed meat, on the other hand, is lower both in overall fat and in artery-clogging saturated fat. It has the added advantage of providing more omega-3 fats. In addition to being higher in healthy omega-3s, meat from pastured cattle is also up to four times higher in vitamin E than meat from feedlot cattle, and much higher in conjugated linoleic acid (CLA), a nutrient associated with lower heart disease and cancer risk that is lacking in our diets. Beware of claims that animals spent most of their life in pasture. When cattle are taken off grass and shipped to a feedlot to be fattened on grain, they immediately begin losing the omega-3s they have stored in their tissues. As a consequence, the meat from feedlot animals typically contains only 15 to 50 percent as much omega-3s as that from grass-fed livestock. Use Label Lookup: Meat Labels to learn more about what claims on meat mean and which ones you can trust.

4. The corn fed to feedlot cattle is fossil-fuel intensive and heavily subsidized.

Our energy-intensive food system uses 19 percent of all the fossil fuel consumed in the United States, more than any other sector of the economy. And it isn't all for powering tractors and farm equipment. Twenty-three million tons of chemical herbicides and fertilizers, all derived from fossil fuel, are used on crops in this country, 10 million tons just on corn. According to Cornell University ecology professor David Pimentel, to make the fertilizer to grow the corn to feed just one feedlot steer during his short life (14 to 16 months, on average) takes about 284 gallons of oil, or 1.2 gallons per bushel.

You might think all that oil would make corn an expensive food source. In fact, it does cost more for the farmers to grow than the feedlot operators pay. But corn is heavily subsidized: over the past decade, the federal government has poured more than $50 billion into the corn industry. The fertilizers plus the subsidies have led to huge surpluses. Add in the USDA's encouragement of farmers to feed the corn to cattle, whether they like it or not, and you’ve got the makings of modern factory farming. Corn is an artificially cheap foodstuff that’s plentiful, compact and portable, making it ideal for quickly feeding tens of thousands of animals on small plots of land.

5. Perennial pasture reduces flooding and pollution-laden runoff.

As noted above, corn and soybean production depletes the soil of its natural health. This greatly diminishes its environmental value, flood control in particular. A stretch of pure prairie will absorb five to seven inches of rain an hour. But when that same land is tilled for corn and soybean production, the normal absorption rate drops to 0.5 inch to 1.5 inches an hour. This meant that when the storms of 2008 brought 12 feet of rain to parts of the Midwest in just 24 hours, catastrophic flooding devastated cities and towns throughout the region. Had upriver land been pasture rather than cornfield, the heavy rains might have produced no runoff.

If more cornfields were converted to perennial grasses, we could significantly reduce the devastation of aquatic life from fertilizer- and herbicide-laden runoff. Consider this: when runoff from the predominantly corn-growing fields of the Midwest reaches the Gulf of Mexico, it contributes to what is known as a dead zone, a seasonal, approximately 6,000-square-mile area that has almost no oxygen and therefore almost no sea life. Because of the dead zone, the $2.8 billion Gulf of Mexico fishing industry loses 212,000 metric tons of seafood a year. Elsewhere around the world, there are nearly 400 similar dead zones. It is sadly ironic that to produce one of the least healthy sources of protein—grain-fed beef—we destroy one of our leanest and healthiest—fish.

6. Grazing animals don't need the large quantities of antibiotics that feedlot cattle do.

Most beef cattle spend their short life in concentrated animal feeding operations (CAFOs), where a thousand or more head of steer are kept in close, concentrated conditions and fattened up for slaughter as quickly as possible. To stay alive and grow in such conditions, farm animals need pharmaceutical help, which can have further damaging consequences for humans. Overuse of antibiotics on farm animals leads, inevitably, to antibiotic-resistant bacteria, and the same bugs that infect animals can infect us, too. The Union of Concerned Scientists estimates that about 70 percent of antimicrobial drugs used in America are given not to people but to animals, which means we're breeding more of those deadly organisms every day. In July 2009, the Obama administration announced that it would seek to ban many routine uses of antibiotics in farm animals in hopes of reducing the spread of dangerous bacteria in humans. Pastured cattle don’t require the drugs their CAFO cousins do. But again, a wise shopper should know that antibiotics are allowed for certain grass-fed certification programs, USDA Process Verified for one, while not for others, such as the American Grassfed Association. Use the label lookup (see #3) to learn more about what claims on meat mean and which ones you can trust.

7. Perennial pasture is a carbon sink.

Agriculture contributes about 30 percent of all global greenhouse-gas emissions. This is much more than the amount emitted by transportation. Production of meat, particularly beef, is a very heavy emitter of carbon dioxide. The United Nations Food and Agriculture Organization reported in 2006 that current production levels of meat contribute between 14 and 22 percent of the carbon dioxide–equivalent gases the world produces every year. See the chart below for a comparison of some common lower- and higher-carbon foods per 100-gram serving.

Beef and dairy production emit particularly high levels of greenhouse gases; producing a given amount of ground beef releases four times as much greenhouse gases as are released in the production of the same amount of pork, 14 times as much as chicken, and 50 to 60 times as much as fruits and vegetables. This is particularly true when the animals are raised in CAFOs where they are fed corn or soybeans. Researchers are finding that tillage systems used to grow row crops release not only carbon dioxide but also nitrous oxide and methane (both global warming gases) by triggering the decay and erosion of topsoil. Without exception, all of the tillage systems examined in a recent study published in Science contributed to global warming, and the worst offenders were conventionally farmed corn, soybeans and wheat.

This is not the case for perennial grass systems. In fact, fields of perennial crops in the same study pulled both methane and carbon dioxide from the atmosphere and stashed them in the soil. There is even some evidence that perennial grasslands are often better at sequestering carbon than forests are. As a consequence, researchers are finding, the production of grass-fed beef yields 40 percent less greenhouse-gas emissions.

8. Modern grazing methods match the efficiencies of industrial-scale grain production.

Modern grass farmers almost universally rely on something called managed intensive rotational grazing. Polywire fences confine a herd of perhaps 60 cows to a small area, maybe one-quarter acre, typically for 12 hours. Then the grazier moves the fence, cycling through a series of such paddocks every month or so. This reflects a basic ecological principle. Left to their own devices in a diverse ecosystem, cows will eat just a few species, grazing again and again on the same plants. Rotational grazing forces them to eat all the available forage, including plants they would normally leave untouched. This produces much more beef or milk per acre than does laissez-faire grazing. But how do modern grazing methods compare in efficiency to industrial-scale grain production? As Todd Churchill, owner of Thousand Hills Cattle in Cannon Falls, Minnesota, reported in the article Graze Anatomy published in OnEarth, he can make more money than a subsidized corn farmer because he can produce about two steers per acre. It takes roughly the same acreage to grow the 3,000 pounds of grain used to finish a single steer in a feedlot.

9. Pastured animals are treated more humanely.

From a humanitarian perspective, there is yet another advantage to pastured-animal products. The cruelties of modern factory farming are severe, with livestock cooped up in cages barely larger than their own bodies, or packed together like sardines for months on end, standing knee -deep in their own manure. Pastured livestock are not forced to live in confinement and to endure the miseries of factory farming. But buyer beware: some beef labels have only vague standards regarding animal welfare, while others have detailed rules that ensure animal health and well-being in a clean, comfortable environment. Use the label lookup feature (see #3) to learn more about what claims on meat mean and which ones you can trust.

10. Grass-fed is more expensive.

Grass-fed beef is more expensive, which means we may eat less of it. This is a good thing, actually, both for our health and for the environment. And honestly, feedlot beef is not really cheaper, not when you add the invisible costs: of antibiotic resistance, environmental degradation, heart disease, E. coli infection, corn subsidies, imported oil and so on. But be advised, while pastured-animal products may have many advantages over factory farm and feedlot products, they are still high in saturated fat (though not as high), still high in cholesterol, and still devoid of fiber and many other essential nutrients. They take less toll on the environment, but the land on which the animals graze still must often be irrigated, thus using up dwindling water resources, and it may be fertilized with petroleum-based fertilizers.

So eat less meat, and when you do, make sure you choose grass-fed, knowing you are supporting a humane, health-promoting, environmentally responsible system of agriculture.

This article is republished with permission from Smarter Living and NRDC.org.

Top 10 reasons to eat grass-fed meat
Taking this step may matter more for the environment and your health than any other food decision you make.