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【科普】肉食话题多棱镜
http://www.sciencemag.org/cgi/content/full/327/5967/810
Erik Stokstad
If people in the developed world ate less meat, it would free up a lot of plants to feed billions of hungry people and gain a lot of good farmland. Some food-security researchers, however, are skeptical; they say the complexities of global markets and human food traditions could also produce some counterintuitive—and possibly counterproductive—results.
Here's a simple idea you may have heard for improving food security: Eat less meat.
The logic—articulated by groups that include the Vegetarian Society of the United Kingdom and the United Nations Environment Programme—goes like this. From chicken cordon bleu to bacon double cheeseburgers, people in the developed world eat a huge amount of animal protein. And consumption of meat, eggs, and milk is already growing globally as people in poorer nations get richer and shift their diets. That's a problem because animals are eating a growing share of the world's grain harvests—and already directly or indirectly utilize up to 80% of the world's agricultural land. Yet they supply just 15% of all calories. So, the argument goes, if we just ate less meat, we could free up a lot of plants to feed billions of hungry people and gain a lot of good farmland.
Some food-security researchers, however, are skeptical. Although cutting back on meat has many potential benefits, they say the complexities of global markets and human food traditions could also produce some counterintuitive—and possibly counterproductive—results. "It's not this panacea that people have put forward," says Mark Rosegrant of the International Food Policy Research Institute (IFRPI) in Washington, D.C. One provocative forecast: If people in industrialized nations gave up half their meat, more Asian children could become malnourished.
Protein-rich
Scholars on all sides of the meaty issue agree on one thing: Just as the rich use more energy than the poor, they also eat more meat. The United States, for instance, has just 4.5% of the world's population but accounts for about 15% of global meat consumption. Americans consume about 330 grams of meat a day on average—the equivalent of three quarter-pound hamburgers. In contrast, the U.S. Department of Agriculture recommends that most people consume just 142 to 184 grams of meat and beans daily. In the developing world, daily meat consumption averages just 80 grams.
Those numbers suggest that people living in the United States and other wealthy nations could increase world grain supplies simply by forgoing that extra burger or chop. But it's not that simple. Figuring out the full impact of meat consumption on global food security requires sophisticated computer models that can track how buying decisions ripple out across farming systems, global supply chains, and food markets.
One of those models is called IMPACT, and in 1998 IFPRI's Rosegrant and colleagues used it to study what might happen in 2020 if rich nations cut their per capita demand for meat to half of what it was in 1993. First, the simulation found that as demand for meat fell, prices declined and meat became more affordable worldwide. As a result, in the developing world, per capita meat consumption actually increased by 13% as poorer consumers could buy more. That's good news for what could be called "meat equity," because increasing animal-protein consumption among the very poor can provide substantial nutritional benefits, particularly for children.
Surprisingly, however, when the rich halved their meat habit, the poor didn't necessarily get that much more grain—their largest source of calories. According to the model, per capita cereal consumption in developing nations rose by just 1.5%. That's enough grain to ease hunger for 3.6 million malnourished children—but nowhere near the kinds of gains many expect from curbing meat consumption.
One big reason is the mismatch between human and animal diets. In rich countries, farmers usually feed their livestock corn or soybeans. When the farmers produce less meat, demand for corn and soy drops and the grains become more affordable. That's good for people in the parts of Africa and Latin America where corn is a dietary staple. But people in many developing countries, particularly in Asia, don't eat much corn; they eat rice and wheat. So falling corn and soy prices don't directly help them. (It's true that as demand for corn drops, some farmers might start growing wheat instead. In general, however, climate, soil, or water availability often limit a farmer's ability to switch crops easily. Iowa soybean growers, for instance, can't start growing rice, which requires heavy irrigation.)
Eating less meat could even backfire and make food insecurity worse, suggested the simulation, which was published in the Proceedings of the Nutrition Society. For instance, when consumers in developed countries replaced meat with pasta and bread, world wheat prices rose. That actually increased malnutrition slightly in developing countries such as India that rely on wheat. "It's a big deal when wheat prices go up," Rosegrant says.
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作者:admin@医学,生命科学 2011-01-29 00:59
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