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新视野大学英语读写教程第三册unit2-aIron and the Effects of Exercise

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Section (A)
Iron and the Effects of Exercise

Sports medicine experts have observed for years that endurance athletes, particularly females, frequently have iron deficiencies. Now a new study by a team of Purdue University researchers suggests that even moderate exercise may lead to reduced iron in the blood of women. "We found that women who were normally inactive and then started a program of moderate exercise showed evidence of iron loss," says Roseanne M. Lyle, associate professor at Purdue. Her study of 62 formerly inactive women who began exercising three times a week for six months was published in the journal Medicine & Science in Sports & Exercise. "Women who consumed additional meat or took iron supplements were able to bounce back," she notes. "But the new exercisers who followed their normal diet showed a decrease in iron levels."


Iron deficiency is very common among women in general, affecting one in four female teenagers and one in five women aged 18 to 45, respectively. But the ratio is even greater among active women, affecting up to 80 percent of female endurance athletes. This means, Lyle says, that "too many women ignore the amount of iron they take in";. Women of child-bearing age are at greatest risk, since their monthly bleeding is a major source of iron loss. Plus, many health-conscious women increase their risk by rejecting red meat, which contains the most easily absorbed form of iron. And because women often restrict their diet in an effort to control weight, they may not consume enough iron-rich food, and are liable to experience a deficiency. "The average woman takes in only two thirds of the recommended daily allowance for iron," notes another expert. "For a woman who already has a poor iron status, any additional iron loss from exercise may be enough to tip her over the edge into a more serious deficiency," notes the expert.


Exercise can result in iron loss through a variety of mechanisms. Some iron is lost in sweat, and, for unknown reasons, intense endurance exercise is sometimes associated with bleeding of the digestive system. Athletes in high-impact sports such as running may also lose iron through a phenomenon where small blood vessels in the feet leak blood. There are three stages of iron deficiency. The first and most common is having low iron reserves, a condition that typically has no symptoms. Fatigue and poor performance may begin to appear in the second stage of deficiency, when not enough iron is present to form the molecules of blood protein that transport oxygen to the working muscles. In the third and final stage, people often feel weak, tired, and out of breath — and exercise performance is severely compromised. "People think that if they're not at the third stage, nothing is wrong, but that's not true," says John L. Beard, who helped design the Purdue study. "You're not stage 3 until your iron reserves go to zero, and if you wait until that point, you're in trouble."


However, most people with low iron reserves don't know they have a deficiency, because traditional methods of calculating the amount of iron in blood (by checking levels of the blood protein that transports oxygen) are not sufficient, Beard states. Instead, it's important to check levels of a different compound, which indicates the amount of storage of iron in the blood. While active, child-bearing age women are most likely to have low iron stores, he notes, "Men are not safe, especially if they don't eat meat and have a high level of physical activity." (An estimated 15 percent of male long distance runners have low iron stores.) Beard and other experts say it's advisable for people in these groups to have a yearly blood test to check blood iron reserves.


If iron levels are low, talk with a physician to see if the deficiency should be corrected by modifying your diet or by taking supplements. In general, it's better to undo the problem by adding more iron-rich foods to the diet, because iron supplements can have serious shortcomings. Supplements may produce a feeling of wanting to throw up, and may be poisonous in some cases. The best sources of iron, and the only sources of the form of iron most readily absorbed by the body, are meat, chicken, and fish. Good sources of other forms of iron include dates, beans, and some leafy green vegetables. "Select breads and cereals with the words 'iron-added' on the label," writes sports diet expert Nancy Clark. "This added iron supplements the small amount that naturally occurs in grains. Eat these foods with plentiful Vitamin C (for example, drink orange juice with cereal or put a tomato on a sandwich) to enhance the amount of iron absorbed." Clark also recommends cooking in iron pans, as food can derive iron from the pan during the cooking process. "The iron content of tomato sauce cooked in an iron pot for three hours showed a striking increase, the level going up nearly 30 times," she writes. And people who are likely to have low iron should avoid drinking coffee or tea with meals, she says, since substances in these drinks can interfere with iron being absorbed into the body.


"Active women need to be a lot more careful about their food choices," sums up Purdue's Lyle. "If you pay attention to warning signs before iron reserves are gone, you can remedy the deficiency before it really becomes a problem."

Words: 900

New Words

▲endurance n. 忍耐,忍耐力
 moderate a. 1.中等的,适中的,适度的 2.中庸的,温和的
 evidence n. 根据,证据,证明
 journal n. 1.日报,杂志,期刊 2.日记
 consume vt. 1.吃,喝 2.消耗,花费(尤指大量地)
 supplement n. 1.增补(物),补充(物) 2.(杂志或报纸的)副刊,增刊
vt. 增补,补充
 bounce v. (使)弹回,(使)反弹
n. 弹,弹力
 respectively ad. 分别地,各自地
 ratio n. 比率
 plus conj. 并且,而且
prep. 加,加上
n. 1.加号,正号 2.有利因素
a. 正的
 restrict vt. 限制,约束
 liable a. 1.易于... ...的,有... ... 倾向的 2.有法律责任的,有义务的
 allowance n. 1.限额,定量 2.津贴,补助,零用钱
 digest vt. 1.消化 2.领会
 digestive a. 消化的
 phenomenon n. 现象
 vessel n. 1.血管,脉管 2.容器,器皿 3.船,舰
 typical a. 典型的,有代表性的
◆typically ad. 典型地,有代表性地
 fatigue n. 疲劳,劳累
 molecule n. 分子
 protein n. 蛋白质
 calculate vt. 1.计算,估算 2.认为,相信,推测
 sufficient a. 足够的,充分的
 compound n. 复合物,混合物
 indicate vt. 1.标示,表明 2.指示方向
 storage n. 储存,储藏
 advisable a. 可取的,适当的,明智的
 yearly a. 每年的,一年一度的
 physician n. 内科医生
 modify vt. 修改,更改,改善
 undo vt. 1.取消,消除 2.解开,松开
 shortcoming n. 缺点
 select vt. 选择,挑选
▲cereal n. 谷类作物,谷类食物(如麦片等)
 plentiful a. 大量的,丰富的
 derive v. 1.得到,获取 2.起源于
 striking a. 1.显著的,突出的,惊人的 2.(由于美貌而)引人注目的,吸引人的
 interfere vi. 1.妨碍,干扰 2.干涉,干预
 remedy vt. 补救,纠正
n. 治疗方法,解决方法

 

Phrases and Expressions

 lead to 导致
 bounce back 恢复正常,恢复过来
 in general 大体上;通常
 up to 至多,多达,直到
 take in 吸入,吞入
 at risk 处在危险之中
 tip over the edge 引起明显变化;(使)进入另一状态
 out of breath 呼吸急促,气喘吁吁
 add sth. to 加,增加,添加
 throw up 恶心,呕吐
 go up (价格、水平等)升高,上升
 sum up 概括,总结

 

Proper Names

 Purdue University 珀杜大学
 Roseanne M. Lyle 罗斯安妮·M.莱尔
 Medicine & Science in Sports & Exercise 《体育运动医学与科学》(期刊名)
 John L. Beard 约翰·L.比尔德
 Nancy Clark 南希·克拉克

    铁质与运动的关系
    运动医学专家经过多年的观察,发现耐力运动员,特别是女性,经常会缺铁。 由珀杜大学一组研究人员进行的一项新的研究表明:即使是适度的锻炼,也可能会降低女性血液中铁离子的含量。
    "我们发现,那些通常不运动的女性一旦开始适度的锻炼,就会出现铁离子含量下降的迹象," 珀杜大学罗斯安妮·M.莱尔副教授说。 她对62名妇女进行了研究,并将研究结果发表在《体育运动医学与科学》杂志上。这些妇女原先不怎么运动,后来开始了为期六个月、每周三次的锻炼。
    莱尔注意到,"那些增食肉类食品或服用铁离子补剂的女性,能够恢复到健康状态。 但突然参加锻炼却仍沿用原来的食谱的人,则显示出铁离子含量的降低。"
    缺铁在多数女性中是很常见的,十多岁的少女四人中有一人缺铁,18至45岁的女性五人中有一人缺铁。 而这一比例在积极锻炼的妇女中数值更高,女耐力运动员中缺铁的则高达80%。 莱尔说,这意味着 "太多女性忽视了自己摄入的铁离子的含量。" 育龄女性危险最大,因为月经是铁流失的重要原因之一。 此外,许多保健意识太强的女性也很危险,因为她们拒绝食用牛肉或羊肉,而这些肉中含有的铁质最易被吸收。 而且,由于女性常常为了控制体重而节食,而未能摄取足够的含铁丰富的食物,结果可能导致缺铁。
    另一名专家注意到,"普通女性只摄入了日需铁含量的三分之一。" 他提醒说,"对于那些已经缺铁的女性,任何因锻炼而产生的更多铁离子流失都足以导致体内缺铁状况的恶化。"
    运动可能通过多种机制导致铁离子流失。 有些铁离子随汗液流失。另外,由于某些未知的原因,高强度的耐力运动有时是与消化系统内出血联系在一起的。 运动员从事高度剧烈的运动,比如跑步时,也可能会因为足部细血管失血的现象而使铁质流失。
    缺铁分为三个阶段: 第一也即最常见的阶段,是铁离子储量不足。这一阶段没有典型症状。 到了缺铁的第二阶段,就会出现疲倦和力不从心,此时体内已没有足够的铁来形成血蛋白分子,将氧输至运动着的肌肉。 在第三也即最后阶段,人常常感到虚弱,疲乏无力,喘不过气,运动成绩大打折扣。
    "人们认为,只要不到第三阶段就不会有什么问题。这种看法是不对的。" 帮助策划珀杜研究的约翰·L.比尔德说。 "只有当你的铁离子储量为零时,你才会进入第三阶段。而你若坐等到这个时候,你的麻烦就大了。"
    然而,比尔德指出,大多数铁离子储量低的人并未意识到自己缺铁,因为传统的检测血液中铁离子储量的方法——只检验血液中输送氧气的血蛋白的含量——是不够的。 其实,有必要检查血液中另一种混合成分的含量,它显示了血液中铁离子的储量。 他还指出,虽然积极锻炼的育龄妇女最有可能铁离子储量低,"但男性也并非不缺铁,尤其是在他们不吃肉类而又从事高强度的体力活动的情况下。" (估计有15%的男性长跑运动员铁离子储量低。) 比尔德和其他专家都说,对这些人而言,最好每年验一次血,以测定血液中铁离子的储量。
    如果铁离子含量低,就要去看医生,以确定是否该通过调整饮食或服用铁离子补剂来校正不足。 一般说来,解决问题的最好方法是在食谱中增加含铁丰富的食物,因为铁离子补剂可能存在严重缺陷。" 服用铁离子补剂可能使人想呕吐,有时甚至还会引起中毒。 最好的铁离子来源,以及惟一最易为身体所吸收的铁离子来源,是肉、鸡和鱼。 其他较好的铁离子来源包括枣、豆类和一些带叶子的绿色蔬菜。"
    "选择那些标有'加铁'字样的面包和麦片," 运动营养专家南希·克拉克写道, "这些增加的铁补充了谷物中自然含铁量的不足。 摄取含有大量维生素C的食物——比如吃麦片时喝橘子汁,或在三明治内夹上番茄——可以促进铁离子的吸收。" 克拉克还建议用铁锅烹食,因为烹调过程中食物能从铁锅中吸收铁离子。 她写道,"在铁锅内烹煮了三个小时的番茄汁,其铁离子含量大大提高,增加到原来的30倍左右。" 她说,铁离子含量可能低的人,吃饭时应避免喝咖啡或饮茶,因为这些饮料中所含的物质会妨碍身体对铁离子的吸收。
    "运动女性应特别注意选择饮食。"珀杜的莱尔总结说, "如果你在铁离子储量流失之前就注意到了警告信号,你就可以在它真正成为问题之前弥补铁离子的不足。"
 

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