八年级生物营养物质

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　　再如：铁是构成血红蛋白的一种成分。缺铁会造成缺铁性贫血，而食物中的铁不易被吸收。而相时而言，具血红素结构的铁就较易吸收，所以补铁方式是，多吃瘦肉、鱼、奶类、蛋、豆类。传统观点是，多吃菠菜补铁。其实，菠菜中含铁2．9毫克／100克，在蔬菜中的确是含量高的，但是，菠菜中含大量的草酸，而草酸会和食物中的钙结合，形成草酸钙沉淀物，影响食物的营养，所以在食用菠菜时，应先用水焯一下。
　　关于各种食物的营养，可参考课本P． 124～P． 128。
　　6．水：
　　最后讲水，水是人体内不可缺少的重要物质，约占体重的60％～70％左右，水是细胞的主要组成成分。人体离不开水。人体内的营养和废物等都必须溶解在水里运输。
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　　DIGESTION　AND　NUTRITION
　　Surrounded by snow and ice， an Aleut hunter slices slabs of raw whale blubber for dinner. 　　In a village in Nepa1， a grandmother eats on1y a bowl of rice， Ten thousand miles away，an American college student downs a bacon cheeseburger， a salad and coffee， Hot chilis， salt-ed fish and cassava tubers.
　　Through it al1，our digestive systems receive whatever we choose to swallow and convert that array of foods into carbohydrates， lipids and proteins the body can use for energy and to build， repair and maintain its role in homeostasis， and thus in survival. The system plays a key consists basically of a food-processing tube and some accessory organs.
　　Many Americans have poor eating habits. They may eat large quantities of snack foods，skip meals， or eat too much and often too fast． Worse yet， the typical American diet tends to be high in fat， cholesterol and salt． The world distribution of some illnesses suggests that the body may pay a high price for certain dietary habits。 For example， in the United States a fat1aden diet is a mayor contributor to health-threatening obesity and heart disease. Obesity a1so increases an adult‘s risk of developing diabetes and contributes to other health prob1ems. In regions where salt-cured and smoke-cured foods are staples，the rates of stomach and esophagus cancer are disturbingly high． Nongenetic colon cancer is much more prevalent among people whose diets lack sufficient fiber，as is common in the United States. Most people of rural Africa and India cannot afford to eat much more than whole grains， which are high in fiber content， and they rarely suffer colon cancer.


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八年级生物营养物质