Jahren A Hope, Kraft Rebecca A
Department of Geology and Geophysics, The University of Hawaii, Honolulu, HI 96822, USA.
Proc Natl Acad Sci U S A. 2008 Nov 18;105(46):17855-60. doi: 10.1073/pnas.0809870105. Epub 2008 Nov 10.
Americans spend >100 billion dollars on restaurant fast food each year; fast food meals comprise a disproportionate amount of both meat and calories within the U.S. diet. We used carbon and nitrogen stable isotopes to infer the source of feed to meat animals, the source of fat within fries, and the extent of fertilization and confinement inherent to production. We sampled food from McDonald's, Burger King, and Wendy's chains, purchasing >480 servings of hamburgers, chicken sandwiches and fries within geographically distributed U.S. cities: Los Angeles, San Francisco, Denver, Detroit, Boston, and Baltimore. From the entire sample set of beef and chicken, only 12 servings of beef had delta(13)C < -21 per thousand; for these animals only was a food source other than corn possible. We observed remarkably invariant values of delta(15)N in both beef and chicken, reflecting uniform confinement and exposure to heavily fertilized feed for all animals. The delta(13)C value of fries differed significantly among restaurants indicating that the chains used different protocols for deep-frying: Wendy's clearly used only corn oil, whereas McDonald's and Burger King favored other vegetable oils; this differed from ingredient reports. Our results highlighted the overwhelming importance of corn agriculture within virtually every aspect of fast food manufacture.
美国人每年在餐厅快餐上花费超过1000亿美元；在美国饮食中，快餐所含的肉类和热量比例过高。我们利用碳和氮稳定同位素推断肉类动物的饲料来源、薯条中脂肪的来源以及生产过程中固有的施肥和圈养程度。我们从麦当劳、汉堡王和温迪连锁店采集食物样本，在美国不同地理区域的城市（洛杉矶、旧金山、丹佛、底特律、波士顿和巴尔的摩）购买了超过480份汉堡、鸡肉三明治和薯条。在整个牛肉和鸡肉样本集中，只有12份牛肉的δ(13)C < -21‰；只有这些动物的食物来源有可能不是玉米。我们观察到牛肉和鸡肉中的δ(15)N值非常稳定，这反映出所有动物的圈养环境一致且都食用了大量施肥的饲料。不同餐厅的薯条δ(13)C值存在显著差异，这表明各连锁店使用了不同的油炸方法：温迪显然只使用玉米油，而麦当劳和汉堡王则更青睐其他植物油；这与成分报告有所不同。我们的研究结果凸显了玉米农业在快餐生产几乎每个环节的压倒性重要性。
