植物学基础3营养与食品卫生

脂类 （Lipids）,单毓娟 ( Dr. & Associated Prof.),第一章 营养学基础, (B703),In the fall of 1995 when 28-year-old skater Sergei Grinkov, a two-time Olympic gold medalist, collapsed and died of a fatal heart attack while training in Lake Placid, New York.,戈尔蒂耶娃格林科夫,一、脂类概述 Introduction of Lipids,Main contents,Introduction of Lipid Lipids in Nutrition Science Classification of triglycerides -3 and -6 fatty acids Fat digestion and absorption Functions of fat Disadvantages of fats Nutritional assessment of dietary fat Dietary reference intakes (DRIs) of fat,4,An autopsy revealed that his coronary arteries were as severely clogged as those of a 70-year-old with established heart disease.,Normal artery containing little cholesterol-rich plaque.,Artery that is partially blocked with plaque, which can lead to a heart attack.,Cholesterol-rich,High fat diet,Heart disease,?,Lipid-Friend or foe?,What causes a heart attack?,Although some people think of dietary fat as something to be avoided, a certain amount of fat is absolutely essential for good health. So what suggestions do you give when people eat foods abundant in fat?,Organic: to describe foods that are grown without the use of non-natural fertilizers or chemicals. Organic: These nutrients contain the element carbon.,两种不同的含义-Organic,甘油三酯的分子结构 Molecular structure of triglycerides,(甘油),(脂肪酸),Triglycerides is a molecule consisting of three fatty acids attached to a three-carbon glycerol backbone.,Most of the fat we eat (95%) is in the form of triglycerides, the same way by which most of the fat in our body is stored. 甘油三酯既是食物中脂肪的主要存在形式，也是机体内脂肪的主要贮存形式,磷脂（Phospholipids）: A type of lipid in which a fatty acid is combined with another compound that contains phosphate; unlike other lipids, phospholipids are soluble in water.,Glycerol,Fatty acid,Fatty acid,Phosphate,Phospholipid,Cell membrane,甘油,脂肪酸,磷脂主要贮存在脑、神经和肝脏中； 磷脂是构成细胞膜的主要成分； 磷脂的主要功能有：提供能量；具有极性和非极性双重特性，有助于物质转运；作为乳化剂，有利于脂溶性物质的吸收、转运及代谢；转运血液中的脂类物质，防治胆固醇在血中的沉积；促进和改善神经系统功能。,A type of lipid found in foods and the body that has a ring structure; these multiple-ring structure is quite different from that of triglycerides.,Sterol ring structure,固醇 Sterols,环状结构,Sterols,Sterols are found in both plant and animal foods and are produced in the body. Plants contain some sterols, but they are not very well absorbed and appear to block the absorption of dietary cholesterol.,Cholesterol,Cholesterol is only found in the fatty part of animal products such as butter, eggs, whole milk, meats and poultry（胆固醇只存在于动物性食品中）. We dont need to consume cholesterol in our diet because our body continually synthesizes it, mostly in the liver and intestines （机体能够合成胆固醇）. Too much consumption is harmful。（胆固醇摄入过多对人体有害）,Cholesterol（胆固醇）,Cholesterol is part of every cell membrane, where it works in conjunction with fatty acids to help maintain cell membrane integrity （保持细胞膜的完整性）. Cholesterol is particularly plentiful in the neural cells that make up our brain, spinal cord, and nerves （神经细胞中含量丰富，参与脑、脊髓和神经等的形成）.,Cholesterol is the essential for life,The body also uses cholesterol to synthesize several important sterol compounds including sex hormones (estrogen, androgen, and progesterone), adrenal hormones, and vitamin D（是合成多种物质的原料：性激素(雌激素、雄激素和黄体激素），肾上腺激素和维生素D.,Phytosterols (植物固醇，也称植物甾醇） are found in plant foods such as cererols, soybeans.And recent studies indicated that they have multiple and beneficial functions for human health.,Phytosterols-good future,Anti-inflammation, regulating blood lipid, blood sugar, anti-cancer（抗炎症、调节血脂、血糖、抗癌等作用）,To understand why someone want more/less of some fats than others we need to know more about their properties and how they work in our body.,三、甘油三酯的分类 Classification of Triglycerides,important,短链脂肪,What information can we get based on this classification？,Fatty acid chain length is important because it determines the methods of fat digestion and absorption and affects how fats function within the body. For example, short- and medium-chain fatty acids are digested and transported more quickly than long-chain fatty acids.,食物中主要是以中链和长链脂肪为主。,Foods:椰子油(coconut oil)和棕榈油(palm oil ) Advantages:,New advanced developments of MCT,1,2,3,消化快 (Fast digestion),吸收快 (Fast absorption),易氧化分解 ( Easy oxygenolysis),Application: 减肥和提高耐力 (Control weight, Improve endurance),Saturated fatty acids are saturated with hydrogen, meaning they have no carbons bonded together with a double bond.（无双键）,Monounsaturated fatty acids contain two carbons bound by one double bond.（1个双键）,Polyunsaturated fatty acid have more than one double bond linking carbon atoms.（2个双键）,Definition,How to feel this difference between saturated and unsaturated？,Long-chain saturated fatty acids stack well together to make solid forms at room temperature.,Mono- and poly-unsaturated fatty acids do not stack well together because they are bent. These fatty acid are liquid at room temperature.,Differences between saturated and unsaturated fatty acids,Types of fatty acid in our foods,Foods can be identified by animal- and plant- foods. Animal fats provide approximately 40 to 60% of their energy from saturated fats While plant fats provide 80 to 90% of their energy from mono- and poly-unsaturated fats.,Major sources of Dietary Fat,Pure foods providing energy,Classified by shapesaturated fat,Molecules of saturated fat are like straight toothpicks: they have no double carbon bonds and always form straight, rigid chains. As they have no kinks, these chains can pack together tightly. That is why saturated fats, such as the fat in meats, are solid at room temperature.,In contrast, each double carbon bond of unsaturated fats gives them a kink along their length. This means that they are unable to pack together. Based on this, unsaturated fats can occur in either a cis or a trans shape. Cisthings are located on the same side or near each other; Transmeans a cross or an opposite.,Classified by shapeunsaturated fat,A cis-fatty acid has both hydrogen atoms located on the same side of the double bond.（氢原子在双键的一侧）,Trans fatty acid has the hydrogen atoms attached on opposite sides of the double carbon bond.（氢原子在双键的两侧）,自然界中存在的脂肪酸主要为 Cis-脂肪酸；食物中也是如此。,Do they both existed in nature and foods？,反式脂肪酸与人体健康,不饱和脂肪酸的不饱和键能与氢结合变成饱和键，随着饱和程度的增加，油类可由液态变为固态，这一过程称为氢化。 在氢化过程中，可能会产生反式脂肪酸。 氢化的作用：提高脂肪的抗氧化作用；改变食物的结构。,反式脂肪酸与人体健康,反式脂肪酸不具有必需脂肪酸的生物活性和对脂蛋白的作用； 流行病资料也显示膳食反式脂肪酸与心脏病之间存在某些联系； 反式脂肪酸的主要食物来源：人造奶油、蛋糕、饼干、油炸食品、乳酪产品、花生酱等食品。,近日，全球最大的快餐集团麦当劳公开承认，在每份麦当劳薯条中，反式脂肪酸含量从过去的6克增加到了8克。在每份麦当劳炸薯条中，不利于身体健康的反式脂肪酸含量比过去增加了1/3。,反式脂肪酸与人体健康,In 2003 the U.S. FDA ruled that trans fatty acids, or trans fats, must be listed as a separate line item on Nutrition Facts labels for conventional foods and some dietary supplements.,尽量避免购买食物标签中标有：植物氢化油、人造黄（奶）油、人造植物黄（奶）油、人造脂肪、氢化油、起酥油等字样的食物。 每周应食用两次鱼，以利于-3 脂肪酸的摄入，从而减少其危害。,如何减少反式脂肪酸的危害？,-3 脂肪酸,四、-3和-6脂肪酸,必需脂肪酸(essential fatty acid，EFA)：是指人体不可缺少而自身又不能合成，必须通过食物供给的脂肪酸。 Definition: EFA are indispensable and must be consumed in the diet because they can not be made by our bodies. 亚油酸(Linoleic acid, LA)和-亚麻酸(-linolenic acid，ALA)是人体必需的两种脂肪酸。,必需脂肪酸 Essential Fatty Acid,必需脂肪酸的功能 Function of EFA,是磷脂的重要组成成分 与精子形成有关 是合成前列腺素的前体 有利于组织修复 与胆固醇的代谢有关,缺 乏,生长迟缓 生殖障碍 皮肤损伤(皮疹等) 其他（心血管疾病等）,-3脂肪酸,EPA and DHA are derived from ALA.,Alpha-linolenic acid (ALA),降低甘油三酯的作用 阻碍甘油三酯掺入到肝的VLDL颗粒中，分泌到血液循环中的甘油三酯减少；降血压作用 。 抗炎症作用 抗癌作用 脑和视网膜发育上的重要物质,-3脂肪酸的生物学功能,-6脂肪酸,亚油酸(LA),花生四烯酸（AA),降低胆固醇的作用 具有促进生长、发育及妊娠的作用 是一些特殊脂类（如磷脂）的组成成分，维持组织膜结构的完整性和最佳的不饱和水平。,-6脂肪酸的生物学功能,-3和-6脂肪酸的食物来源,-3脂肪酸:主要存在于鱼油(Fish oil) 和鱼类产品( fish products) 。 -6脂肪酸:主要存在于植物油中,如葵花油(sunflower oil) 、 红花油(safflower)、玉米油(corn oil) 、豆油(soy oil)和 花生油(peanut oil)。,-3和-6脂肪酸的比例,人类最早食用的基本都是野生植物和散养动物，食物中的-3和-6有着严格比例,基本保持平衡。 工业化时代，人类大量食用加工和养殖产品，使得体内所含-6越来越多，比例严重失调。 据估计，目前美国等发达国家里，人体内的-6和-3比例可能达到30：1，甚至达50：1。 北京儿童医院与瑞典皇家医院在河北石家庄地区的调查，该地区妇女-6和-3的比例在26：1,-3脂肪酸有益的生物学功能,过多-6脂肪酸有害的生物学功能,Because fats are not soluble in water, they cannot enter our blood stream easily from the digestive tract. Thus, fats must be digested, absorbed, and transported within the body differently from other water-soluble nutrients.,五、脂肪的消化、吸收 Fat digestion and absorption,Mouth: Salivary glands in the mouth produce an enzyme, lingual lipase, that digests some triglycerides. Salivary enzymes have a limited role in the breakdown of fats.,Fat digestion- in mouth,Partially digest,Moisture and chew,Fat digestion- in Stomach,Fat arrives intact at the stomach where it is mixed and broken into droplets. Gastric lipase digests some triglycerides. Because they are not soluble in water, these fat droplets typically float on top of the watery digestive juices in the stomach until they are passed into the small intestine.,As fat enters the small intestine from the stomach, the gallbladder contracts and releases bile, which acting much like soap, breaking down the fat into smaller and smaller droplets. At the same time, lipid-digesting enzymes produced in the pancreas travel into the small intestine.,Two organs assisting fat digestion,Do you remember the structure of triglycerides？,Once bile has broken the fat into small droplets, these pancreatic enzymes take over, breaking the fatty acids away from their glycerol backbones (Real breakdown). Each triglyceride molecule is broken down into two free fatty acids and one monoglyceride (one fatty acid was left). In this case, a glycerol molecule with one fatty acid still attached.,Fat digestion in the small intestine,The majority of fat absorption occurs in the mucosal lining of the small intestine with the help of a micelle. A micelle is a spherical (round) compound that can trap the free fatty acids and the monoglycerides and transport them to the mucosal cells for absorption.,Fat absorption-primarily in the small intestine,Because fats do not mix with water, most fats cannot be transported freely in the bloodstream. How does the absorbed fat get into the blood stream?,To solve this problem, the fatty acids are reformulated back into triglycerides and then packaged into lipoprotein before being released into the bloodstream. Why lipoprotein can be absorbed into the bloodstream?,Structure of a lipoprotein,Lipoprotein is a spherical compound in which the fat clusters in the center and phospholipids and proteins form the outside of the sphere.,Chylomicron（乳糜微粒） is a specific lipoprotein produced in the mucosal cell of the intestine to transport dietary fat out of the intestine tract into the blood. Chylomicron is a fat carrier in the small intestine.,Have you remembered? I mentioned that the short- and medium-chain fatty acids are digested more quickly than long-chain fatty acids?,Why?,When short and medium-chain fatty acids are digested and transported to the mucosal cell of the small intestine, they do not have to be reformed into triglycerides and incorporated into chylomicrons. Instead, they can travel in the bloodstream bound to either a transport protein or a phospholipid.,It should be mentioned that two following lipoprotein served as transporter in different way Low density lipoprotein（LDL）：less triglycerides， more cholesterols High density lipoprotein（HDL): carry cholesterol back to liver for breaking down,Transport of fat in the body,Obviously.,How does our body deal with fat absorbed？,There are three primary fates of the fat absorbed. It can immediately be taken up and used as a source of energy for the cells. It can be used to make lipid-containing compounds (some examples?) in the body. It can be stored in the muscle or adipose tissue as a triglyceride for later use.,六、脂肪的功能 Functions of Fat,1,提供能量和贮存能量（Provide and store energy）,Fat provide 9 kilocalories (kcals) per gram. Fat is a primary source of energy. 特点：不能给脑、神经细胞和红细胞提供能量,2,保持体温正常（Maintain body temperature）,How much energy for protein?,3,4,维持细胞功能及保护机体 （Help maintain cell function and provide protection to the body）,5,提供必需脂肪酸 （Provide essential fatty acid）,内分泌作用（Endocrine secretion） 瘦素,Functions of Fat,更有效地利用碳水化合物和节约蛋白质作用 （Utilize more effectively carbohydrates and protein sparing action ）,转运脂溶性维生