一 碳水化合物的定义 What are carbohydrates? 碳水化合物 : 属三大能量营养素之一, 主要由碳 氢 氧构成 碳水化合物 Carbohydrates Carbohydrate can be abbreviated as CHO. 二 碳水化合物的分类 Classification of carbohydrates Simple Monosaccharide 单糖 Disaccharides 双糖 Carbohydrates Complex Oligosaccharide 寡糖 Polysaccharides 多糖 Monosaccharides-Glucose( 葡萄糖 ) 食物中最多的单糖, 但不以单独形式存在, 常与其他糖形成双糖或多糖的形式存在, 葡萄糖优先为大脑提供能量 Prefix Monosaccharides-Fructose( 果糖 ) Fructose is also called fruit sugar. Fructose is the sweetest natural sugar, occurs naturally in fruits and vegetables. Monosaccharides-Galactose( 半乳糖 ) Galactose does not occur alone in foods. It joins with glucose to create lactose, one of the disaccharides. 1
Disaccharide( 双糖 ) Disaccharide: A carbohydrate compound consisting of two sugar molecules joined together. The three most common disaccharides found in foods are lactose( 乳糖 ), maltose ( 麦芽糖 ), and sucrose ( 蔗糖 ). Disaccharides Lactose( 乳糖 ) Lactose: Consist of one glucose molecule and one galactose ( 半乳糖 ) molecule. + Glucose Galactose Lactose Disaccharides Maltose ( 麦芽糖 ) Maltose: also called malt sugar, consist of two molecules of glucose. It does not generally occur by itself in foods, but results as a by-product of digestion. Glucose + Disaccharides Sucrose( 蔗糖 ) Sucrose is composed of one glucose molecule and one fructose( 果糖 ) molecule. + Sweeter than lactose or maltose, why? How about the Sucrose and fructose? Sucrose provides much of the sweet taste found in honey, fruits, and vegetables. Oligosaccharide( 寡糖 ) Oligosaccharide are composed of 3 to 10 monosaccharides. The most common oligosaccharides are raffinose ( 棉籽糖 )and stachyose( 水苏糖 ). They can not be degraded by enzymes in the small intestine, but can be broke down in the large intestine. Polysaccharides( 多糖 ) Polysaccharides include starch( 淀粉 ), glycogen( 糖原 ) and most fibers( 纤维 ). 2
Polysaccharides ( 多糖 ) Polysaccharide--Starch( 淀粉 ) Starch: A polysaccharide stored in plants and is the storage form of glucose in plants.( 淀粉是葡萄糖在植物中的贮存形式 ) Starch 淀粉 Glycogen 糖原 Fiber 纤维 Excellent food sources of starch include? grains (wheat, rice, corn, oats, and barley), legumes (peas, beans, and lentils), and tubers (potatoes and yams). Our bodies easily digest most starches, we call them digestible starch( 可吸收淀粉 ). 根据其结构可分为直链淀粉 (amylose) 和支链淀粉 (amylopectin), 前者易使食物老化, 后者易使食物糊化 (gelatinization ) However, some starch in plants is not digestible and is called resistant starch( 抗性淀粉 ). 抗性淀粉 : 指健康者小肠中不吸收, 但在大肠中可被大肠菌丛发酵利用的淀粉 在大肠中被生理性细菌发酵, 产生短链脂肪酸与气体, 刺激有益菌生长 ; 不会提升体内的血糖浓度, 对胰岛素分泌的影响极小, 宜于血糖不稳定或高血糖患者食用 When our intestinal bacteria try to digest resistant starch, a fatty acid called butyrate is produced. Consuming resistant starch may be beneficial because butyrate is suggested to reduce the risk of cancer. 豆科食物 (Legumes) 含有的抗性淀粉比谷类 蔬菜和水果多 Polysaccharide-Glycogen( 糖原 ) Glycogen: A polysaccharide stored in animals, including humans. Very little glycogen exists in food. Thus, glycogen is not a dietary source of carbohydrate. Green soybean Bean sprout 3
Polysaccharide--Fiber Based on the water soluble ability, fiber can be classified into soluble fibers and insoluble fibers. Insoluble fibers( 不溶性纤维 ): cellulose ( 纤维素 ), hemicellulose( 半纤维素 ) and xylogen( 木质素 ). Soluble fibers( 可溶性纤维 ): 果胶 (pectin), 树胶和粘胶. 膳食纤维 (dietary fiber): 是指植物性食物或原料中糖苷键大于 3 个, 不能被人体小肠消化和吸收, 但对人体健康有意义的碳水化合物 膳食纤维包括部分非淀粉多糖 ( 纤维素 半纤维素 木质素 果胶等 ) 抗性淀粉 h1 h2 葡聚糖以及部分低聚糖等 Functions of dietary fiber (1) 增强肠道功能 有利粪便排出 膳食纤维能吸收水膨胀, 增大肠内容物体积, 使大便变软变松, 还能促进肠蠕动, 缩短肠内容物通过肠道的时间, 能起到防治便秘和痔疮的作用 (2) 控制体重和减肥 膳食纤维在胃肠内容易产生饱腹感, 能帮助减肥者有效地控制食欲, 而且膳食纤维可限制部分糖和脂质的吸收, 使体内脂肪消耗增多 (3) 降低血糖和血胆固醇可溶性膳食纤维吸水后膨胀为凝胶状, 能增加食物的黏滞性, 还能在小肠黏膜表面形成一层 隔离层, 延缓食物中葡萄糖的吸收 ; 同时增加饱腹感, 可防止餐后血糖急剧上升 膳食纤维还可以增加胰岛素的敏感性 美国糖尿病学会建议糖尿病病人每天摄取的膳食纤维应达 40 克 膳食纤维可以减少肠道对胆固醇的吸收, 促进胆汁的排泄, 降低血胆固醇水平, 可预防冠心病和胆石症的发生 (4) 降低结肠癌的发病风险膳食纤维能促进肠道蠕动, 缩短了食物分解产生的某些毒素及黄曲霉毒素 亚硝胺 多环芳烃等致癌物在肠道内的停留时间, 减少肠道对毒物的吸收, 预防结肠癌 (5) 其它 : 防治痔疮 大便秘结 ; 防胆结石等 4
幻灯片 20 h1 h2 寡糖王松梅, 2014/9/11 属于多糖王松梅, 2014/9/11
三 膳食纤维过量的危害作为食品, 膳食纤维本身并不具有毒性, 但是有些疾病病人不宜多食膳食纤维 : 各种急性慢性肠炎 伤寒 痢疾 肠道肿瘤 消化道小量出血 肠道手术前后 肠道食道管腔狭窄 某些食道静脉曲张 过量的膳食纤维导致腹泻 胀气 肠梗阻 ; 还会影响一些维生素和微量元素的吸收 三 碳水化合物的消化及吸收 ( 自学 ) We have learned many forms of CHOs containing in our foods, which one is the form of energy used by our bodies? The primary goal of CHO digestion is to break down polysaccharides and disaccharides into monosaccharides that can be converted to glucose. Digestion of carbohydrates in foods (In the mouth) Question: When you eat steamed bread ( 馒头 ), notice that you can actually taste it becoming sweeter, Why? Saliva amylase( 淀粉酶 ) breaks starch( 淀粉 ) into smaller particles and eventually into the maltose( 麦芽糖 ). CHO digestion begins in the mouth. Disaccharides are not digested in the mouth. Digestion of carbohydrates in foods (In the stomach) In the stomach, all digestion of CHOs ceases. Would you guess the reasons? Because the acid in the stomach inactivates most of the salivary amylase enzyme. Digestion of carbohydrates in foods (In the small intestine) The majority of carbohydrate digestion occurs in the small intestine. Pancreatic amylase secreted by the pancreas into the small intestine. Pancreatic amylase continues to digest any remaining starch into maltose( 麦芽糖 ). 5
Additional enzymes found in the intestinal tract break down disaccharides into monosaccharides. 麦芽糖 蔗糖 乳糖 Maltose Sucrose Lactose Transform of carbohydrates in the liver Blood vessels Fructose&galactose Glucose Maltase Sucrase Lactase Glycogen Energy Glucose Glucose & Fructose Glucose & Galactose Blood vessels Absorbed by mucosal cells Blood stream Cell Transform of carbohydrates in the liver Excess glucose can be transformed and stored as glycogen in liver and muscles. Our liver can store 70g (or 280 calories) of glycogen. Our muscles can normally store about 120 g (or 480 cal) of glycogen. Liver glycogen:maintains blood glucose levels, provide the needs of our cells, including those of our brain, spinal cord and red blood cell. In addition, It provide energy to the muscles during intense exercise( 剧烈运动 ). Digestion of carbohydrates in foods (In the large intestine) We do not possess enzymes that can break down fiber. Thus, fiber passes through the small intestine undigested and enters the large intestine or colon. There is no any digested process for fiber Once into the large intestine, bacteria break down some undigested carbohydrates, causing the production of gas and a few fatty acids( 产酸 产气 ). The cells of the large intestine use these fatty acids for energy. The fiber remaining in the colon adds bulk to our stools and is excreted in feces. 6
Monosaccharides travel to liver in bloodstream, then to cells to provide energy; Excess glucose is stored as glycogen in liver. Bacteria break down some undigested CHO; remaining fiber is excreted in feces. Summary Salivary amylase breaks down starch into shorter polysaccharides and a few maltose. No digestion takes place Pancreatic amylase is secreted into small intestine. Majority of starch were digested. Pancreatic amylase Specific enzymes ; All monosaccharides are absorbed by small intestine and enter bloodstream. 四 碳水化合物的功能 Function of carbohydrates 1. 提供和贮存能量 (provide and store energy) How much? 4kcal/g. Some of our cells can also use fat and even protein for energy if necessary. However, our red blood cells can utilize only glucose and our brain & other nervous tissues primarily rely on glucose. Amounts of carbohydrate and fat used during the different extent of exercise. Function of carbohydrates Carbohydrate 2. 节约蛋白质作用 (CHOs spare proteins) Percent contribution to total energy 13% 87% Fat 45% 55% 67% 33% Fat breakdown is a slow process and require oxygen we can break down glucose very quickly either with or without oxygen. 定义 : 当摄入足够的碳水化合物时, 可以防止体内和膳食中的蛋白质转变为葡萄糖. 糖异生 (gluconeogenesis) Gluconeogenesis: The generation of glucose from the breakdown of protein into amino acids. Light Moderate Intense Function of carbohydrates When our body uses proteins for energy, the amino acids from these proteins cannot be used to make new cells, repair tissue damage, support our immune system, or perform any of their other functions. Using amino acids in this manner over a prolonged period of time can cause serious, possibly irreversible, damage to these organs. 3. 抗生酮作用 (Prevent the generation of ketones) Low carbohydrate intake can lead to ketoacidosis( 酮症酸中毒 ) 食物中碳水化合物不足, 机体要利用储存的脂肪来供给能量 但机体对脂肪酸的氧化能力有一定限度 动用脂肪过多, 其分解代谢的中间产物 ( 酮体 ) 不能完全氧化, 会引起酮病 低血糖病 妊娠毒血症 7
Functions of carbohydrates 五 碳水化合物代谢相关疾病 4. 机体的构成成分 : 核糖和脱氧核糖是细胞中核酸的成分 ; 糖脂是组成神经组织与细胞膜的重要成分 ; 糖蛋白是抗体 酶 激素以及肝素的组成部分 5. 改变食物的色 香 味 型 6. 提供膳食纤维 糖尿病 低血糖症 乳糖不耐症 血糖的调节过程 Glucose molecules are too large to cross the cell membranes of our tissues independently. To get in, glucose needs assistance from the hormone insulin. Insulin secreted by pancreas enters bloodstream Tissue cell membrane When blood glucose is high Insulin stimulates glucose transport into cell Glucose in blood enters cells When blood glucose is low Glucagon secreted by pancreas enters bloodstream Liver cell membrane 胰高血糖素 Glucagon stimulates glycogen breakdown Glucose is secreted into bloodstream and transported to cells Normally, insulin and glucagon balance each other to maintain blood glucose within a healthy range. If this balance is altered, it can lead to health conditions such as diabetes( 糖尿病 ) or hypoglycemia( 低血糖症 ). 8
血糖指数 (Glycemic index,gi) 定义 :50g 含碳水化合物的食物血糖应答曲线下面积与同一个体摄入 50g 碳水化合物的标准食物 ( 葡萄糖或面包 ) 血糖应答曲线下面积之比 血糖指数是食物升高血糖潜力的一个参考指标, 反映了食物对血糖的影响程度 高 GI 食物能使血糖突然升高 血糖指数的应用 指导合理膳食, 有效控制血糖糖尿病人低血糖症患者 运动员 有助于控制体重 改善胃肠道功能 部分常见食物的 GI 乳糖不耐症 (Lactose intolerance) 食物大米饭酸奶 GI 88 83 食物柚子鲜桃 GI 25 28 食物熟香蕉猕猴桃 GI 52 52 Lactose intolerance: A disorder in which the body does not produce sufficient lactase enzyme ( 乳糖酶 ) and therefore cannot digest foods that contain lactose, such as cow s milk. 牛奶 27.6 梨 36 芒果 55 鲜豆腐生香蕉 31.9 30 苹果柑 36 43 菠萝西瓜 66 72 主要症状 : 胃肠不适 胀气 痉挛和腹泻等 乳糖不耐受的防治措施 : (1) 正确的饮奶方法 : 少量多次饮牛奶 ; 将牛奶和其它固体食物, 如面食 饼干等一起食用可以避免或减轻, 要尽量避免空腹饮奶 (2) 选择低乳糖配方奶粉或饮用豆浆 (3) 饮用酸奶, 酸奶中含有的活菌如乳酸杆菌 嗜热链球菌等含有 β- 半乳糖苷酶活性, 可以分解乳中的乳糖 (4) 严重者暂停饮奶 长期不饮奶者, 适当补充钙剂 六 膳食参考摄入量 Dietary reference intakes 中国营养学会推荐我国居民的碳水化合物的膳食推荐摄入量占总能量的 55%~65%, 其中精制糖占总能量 10% 以下 9
食物中碳水化合物的含量 (g/100g) 膳食纤维建议摄入量 名称猪肉牛肉鸡肉鸡蛋牛奶酸奶鲤鱼带鱼 含量 2.4 2.0 1.3 2.8 3.4 9.3 4.1 3.3 名称黄豆小麦粉稻米玉米面小米马铃薯绿豆大白菜 含量 34.2 73.6 77.9 75.2 75.1 17.2 62.0 3.2 预防医学第 5 版 中国营养学会 2000 年推荐 能量 (Kcal ) 1800 2400 2800 膳食纤维 (g/d) 25 30 35 其中 : 不可溶性膳食纤维占 70-75%, 可 溶性膳食纤维占 25-30% 美国 FDA 提倡每人每天摄入纤维 25g, 或每天按 11.5g/Kcal 摄入较为合适 小结 碳水化合物的分类及功能 膳食纤维的定义及功能 乳糖不耐症 10