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本视频由营养师团HealthCrew翻译制作
Fats are an essential part of a healthy diet.
脂肪是健康膳食中必不可少的一部分
They contribute to the taste and texture of foods, like the smoothness of guacamole and the flakiness of a croissant.
它们有助于提高食物的口感和质地 比如牛油果酱的顺滑和羊角面包的蓬松感
Fats are also a major source of energy, a critical component of cells and tissues, and
脂肪也是能量的主要来源 是细胞和组织的重要组成部分
they also absorb essential vitamins, and can be converted into other molecules like prostaglandins
它还可以促进必需维生素的吸收 也能被转化成其它的分子 比如前列腺素
which help cells communicate with one another.
后者参与细胞间信息传递
Fats have a three carbon backbone called glycerol, as well as fatty acid chains.
脂肪的结构是一个三碳主链 称之为甘油 和脂肪酸链
The fatty acid chain is basically a string of carbon and hydrogen atoms.
脂肪链本质上就是一串碳原子和氢原子
When an “OH” from the glycerol molecule binds to an “H” from the fatty acid, an
当甘油分子中的羟基“OH”与脂肪酸的氢“H”结合时
“H20” - a water molecule - gets released, and the two molecules link up.
一个“H2O”-水分子-被释放 甘油与脂肪酸两个分子连接起来
If this happens once, the result is a monoglyceride, if it happens twice it’s a diglyceride,
这一反应发生一次 生成的是甘油一酯 发生两次便是甘油二酯
and three times makes a triglyceride.
发生三次便是甘油三酯
Now, there are various types of fatty acid chains, and one way to categorize them is
有各种各样的脂肪酸链 一种分类方法是根据它们的长度
by their length, in other words, how many carbons they have.
换句话说 即它们有多少个碳原子
Short chain fatty acids have 2 to 5 carbons, medium chain fatty acids have 6 to 12 carbons,
短链脂肪酸有2到5个碳原子 中链脂肪酸有6到12个碳原子
and long chain fatty acids have 13 or more carbons.
长链脂肪酸有13或更多个碳原子
Fatty acid chains are also categorized by the bonds connecting the carbons in the chain.
脂肪酸链也可根据碳碳键而进行分类
A single bond is just one bond between the carbon atoms, and when a fatty acid chain
单键是指碳原子间以一个键相连
has only single bonds, it’s called a saturated fatty acid - because it has as many hydrogen
当脂肪酸链只有单键时 它被称为饱和脂肪酸 因为它含有的氢原子不可能再多
atoms as possible - it’s saturated with them.
已经达到饱和状态了
Triglycerides with saturated fatty acids are nice and straight so they pack together really
含有饱和脂肪酸的甘油三酯呈直链
well, and as a result they’re usually solid at room temperature.
所以它们能很好的聚集在一起 因此在室温下通常是固态
And the longer the saturated fatty acid chain, the more likely it will be solid at room temperature.
饱和脂肪酸链越长 室温下就越容易呈固体状态
Carbons can also have double bonds between them, and when a fatty acid has one or more
碳原子之间也有双键 当脂肪酸有一个或多个双键时
double bonds, it’s called an unsaturated fatty acid because it’s not saturated with hydrogen atoms - for every double bond there are two fewer hydrogen atoms.
它被称为不饱和脂肪酸 因为此时的氢原子没有饱和 一个双键就意味着少了两个氢原子
Also a double bond causes a kink in the molecule so the triglycerides don’t pack together
双键会导致分子发生扭曲 因此含有不饱和脂肪酸的甘油三酯
as nicely as saturated fats.
不像饱和脂肪那样能完美的聚集在一起
As a result, unsaturated fats are usually liquid at room temperature.
因此 不饱和脂肪在室温下常是液体
Unsaturated fatty acids can be further classified, according to the number of their double bonds.
不饱和脂肪酸可被进一步分类 根据双键数量的不同
Monounsaturated Fatty acids are fatty acids with only a single double bond.
单不饱和脂肪酸是只有一个双键的脂肪酸
Polyunsaturated fatty acids have two or more double bonds.
多不饱和脂肪酸有两个或更多双键
Also, they can be classified according to their location as well, since these hydrogens
此外 还可以根据双键的位置来进行分类
can get kinda crazy, we’ll take them away for now.
这些氢原子使得脂肪酸链的结构看起来很复杂 我们先暂时不管它
So, we also call the methyl end the omega end, and and then we count the number of carbons until the first double bond.
我们称甲基端为Ω端 然后从这里对碳进行计数 直到出现第一个双键
Since this one’s three, it would be an omega-3 fatty acid.
这个分子中 我们数到了3 因此它是Ω-3脂肪酸
If the double bond is 6 carbons from the end, it’s omega-6, and if it’s 9 carbons from
如果双键处于第6个碳原子位置上 就是Ω-6脂肪酸
the end, it’s called omega-9. Now, to make things even easier, I’m just going to show the bonds. Alright, so omega 3’s are usually polyunsaturated fatty acids, and include alpha-linolenic acid,
如果在第9个碳原子位置上 就是Ω-9脂肪酸 现在 为了让这些分子看起来更加的简单易懂 我将只用碳键来表示其结构 Ω-3通常是多不饱和脂肪酸
包括α-亚麻酸（ALA）
or ALA eicosapentaenoic acid, or EPA, docosahexaenoic acid, or DHA.
二十碳五烯酸（EPA）二十二碳六烯酸（DHA）
EPA and DHA are marine sources of omega-3’s.
EPA和DHA是海洋中Ω-3的来源
They’re produced by microalgae, and end up in the tissues of fish like anchovies,
它们是由微藻产生的 最终会富集在鱼的体内
mackerel, salmon, and sardines.
如凤尾鱼 鲭鱼 鲑鱼 沙丁鱼
ALA is found in plants like flaxseed, walnuts, and canola and soybean oils.
ALA存在于亚麻籽、核桃、菜籽油和大豆油等植物中
Our bodies can convert ALA into EPA and DHA, but it’s an inefficient process that yields only small quantities, and that’s why dietary recommendations include foods that have EPA and DHA.
在我们体内 ALA可以被转化为EPA和DHA 但这一过程效率较低 只能产生少量的EPA和DHA 这就是为什么建议摄入含有EPA和DHA的食物
Omega-6 polyunsaturated fatty acids are also usually polyunsaturated, and include and linoleic
Ω-6不饱和脂肪酸也是多不饱和脂肪酸
acid and arachidonic.
包括亚油酸和花生四烯酸
Linoleic acid is found in oils like safflower, corn, and soybean oils.
亚油酸存在于红花、玉米和大豆油等食用油中
Arachidonic acid is found in animal sources like fish, meat, and eggs.
花生四烯酸的主要来源是动物 如鱼类 肉类和鸡蛋
Our bodies can convert linoleic acid into arachidonic acid, but once again the process
机体可以将亚油酸转化为花生四烯酸
is inefficient.
但这一过程同样效率低下
Because ALA and linoleic acid can only be obtained in the diet, they are considered
因为ALA和亚油酸只能通过饮食获取
essential fatty acids.
因此它们被认为是必需脂肪酸
Omega-9 fatty acids are typically monounsaturated fatty acids, and an example would be Oleic
Ω-9通常是单不饱和脂肪酸 一个例子是油酸
acid, these can be made by the human body.
这些脂肪酸可以在体内生成
Foods like canola and olive oil, as well as almonds contain omega-9s.
像菜籽油 橄榄油这样的食物 还有杏仁
Now, looking at the double bond of this unsaturated fatty acid, like most unsaturated fats, it’s
都含有Ω-9系列脂肪酸 像大多数不饱和脂肪一样
got a cis configuration.
不饱和脂肪酸的双键存在顺式构型
In a cis configuration, the two functional groups are on the same side of the double-bonded
顺式构型中 两个官能团在碳碳双键的同侧
carbons. Now when this happens, the fatty acid chain naturally bends.
当这种情况发生时 脂肪酸链会自然弯曲
A molecule that bends doesn’t pack tightly together, so it’s a lot more fluid - think
一个弯曲的分子无法紧密的聚集在一起 所以它更可能为液体状态 想想烹饪用油
about cooking oils, which are liquid at room temperature.
他们在室温下便是液体
Some fats are in a trans configuration, though.
一些脂肪酸是反式构型
In a trans configuration, the functional groups are on opposite sides of the double-bonded
在反式构型中 官能团分别位于碳碳双键的两侧
carbons. This keeps the chain more straight and easier to pack.
这使分子链呈直线 容易聚集在一起
Trans fats result from a process called partial hydrogenation.
反式脂肪是在部分氢化的过程中产生的
In just hydrogenation, hydrogens are added to cis-fats to get rid all the double bonds
在氢化过程中 氢原子被添加到顺式脂肪中
double bond, so let’s say you’ve got this triglyceride, it has a total of two double bonds, so we’d add 4 hydrogens, 2 for each double bond.
消除所有的双键 以甘油三酯例为 它有两个双键 我们加4个氢 给每个双键2个
That turns the unsaturated fatty acids with cis double bonds into saturated fatty acids!
这使得有顺式双键的不饱和脂肪酸 变成饱和脂肪酸
Partial hydrogenation, on the other hand, refers to adding hydrogens to most but not all double bonds.
与之不同的是 部分氢化 是指把氢原子加到大多数但不是所有的双键上
Let’s say now we just add 2 hydrogens.
假设现在只加2个氢
When this happens, some double bonds can be turned into single bonds by the hydrogens,
当这种情况发生时 一些双键可以通过加氢 变成单键
but then reform, and what you end up with is an unsaturated fat but some that have trans double bonds. Partial hydrogenation is a process that occurs naturally in the digestive tract of some animals
结构重组之后 最终得到的是含有反式双键的不饱和脂肪酸 部分氢化会在某些动物的消化道中自然发生
like cows and pigs, which is why trans fats can be found naturally in meat and dairy products.
比如牛和猪 这就是为什么反式脂肪可以在肉类和奶制品中找到
Trans fats are also created through the partial hydrogenation of liquid oils a process that
反式脂肪也可通过液态油的部分氢化而产生
makes them solid..
经这一过程后 液态油便成为固体
Partially hydrogenated oils have been largely removed from foods in North America and Europe
由于反式脂肪与冠心病有关
because trans fats have been associated with coronary heart disease.
部分氢化油已基本从北美和欧洲的食品中去除了
Although some foods may have more of one type of fat than another, the truth is that all
尽管一些食物中含有的某种脂肪多于另一种脂肪
foods are made up of a blend of fatty acids.
但事实是 所有的食物都是由多种脂肪酸组成的
When you eat a food like peanut butter, which has about 75% of its calories from fat, the
当你吃像花生酱这样的食物时 约75%的总热量来源于脂肪
body goes through a set of steps to digest and absorb the fatty acids.
机体需要通过一系列的过程来消化吸收脂肪酸
First of all, triglycerides are hydrophobic.
首先 甘油三酯是疏水的
So they form large globules of fat - like what you see when you pour oil into water.
所以脂肪形成了较大的油滴 就像你把油倒进水中所看到的一样
Enzymes called lipases in the saliva, stomach, and secreted by the pancreas can break down
存在于唾液和胃中 以及胰腺分泌的脂肪酶
triglycerides into free fatty acids and monoglycerides.
可以将甘油三酯分解为游离脂肪酸和甘油一酯
But working on the surface of a globule is inefficient, so to speed things up, bile salts
由于在大油滴表面作用效率低下 为加快速度 肝脏会产生胆汁盐
produced by the liver, break the large fat droplet into smaller droplets which increases
将大的脂肪滴分解为较小的油滴
the surface area for the lipases to work.
使脂肪酶的接触面积增加
Once the triglycerides are broken down into monoglycerides and free fatty acids, these
一旦甘油三酯分解为甘油一酯和游离脂肪酸
self-assemble into mixed micelles which have and a hydrophobic interior. and hydrophilic or water loving exterior.
这些分子便会自己形成内部输水 外部亲水的混合胶粒
The micelles glide through the watery environment of the intestinal lumen, and reach the enterocytes in the intestinal wall.
这些胶粒能穿过肠腔的水性环境 到达肠壁的肠细胞
When they get to the enterocytes, the micelles release the fatty acids and monoglycerides,
当它们到达肠细胞时 胶粒释放出脂肪酸和甘油一脂
which diffuse into the enterocyte.
后者扩散进入肠细胞
Inside the enterocyte, the fatty acids and monoglycerides reassemble into triglycerides,
在肠细胞内 脂肪酸和甘油一脂重新组合成甘油三酯
and these get packed into a larger structure called a chylomicron.
它们被包裹成一个更大的结构 叫做乳糜微粒
The chylomicron has lipids and proteins - so it’s a lipoprotein.
乳糜微粒含有脂质和蛋白质
It has an outer membrane with phospholipids and proteins, and a hydrophobic core that
所以它是脂蛋白 乳糜微粒的外膜含有磷脂和蛋白质
contains triglycerides, cholesterol, and fat-soluble vitamins A, D, E and K.
疏水的内核含有甘油三酯 胆固醇和脂溶性维生素A、D、E和K
The chylomicron then leaves the enterocyte.
之后 乳糜微粒离开肠细胞
It’s too large to get into the endothelial cells, so instead it enters a nearby lymphatic capillary called a lacteal.
由于它太大了 无法进入内皮细胞 它便进入了附近的淋巴毛细管 即乳糜管
From there, the chylomicron floats in the lymph and flows into the thoracic duct, and
从那儿 乳糜微粒悬浮在淋巴液中
then gets dumped into the blood - essentially bypassing the portal vein.
流入胸导管 之后进入血液 这一过程绕过了门静脉
Once in the blood, the chylomicron releases fatty acids and monoglycerides in peripheral
在血液中 乳糜微粒可以在周围组织内释放出脂肪酸和甘油一脂
tissues like muscle which use them for energy, as well as adipose tissue which can store
比如 在肌肉组织中用来供能 也可以在脂肪组织中进行储存
them. After delivering the triglycerides, the chylomicron shrinks in size and eventually gets engulfed
在完成甘油三酯转运后 乳糜微粒的体积缩小
by the liver.
最终会被肝脏吞噬
Now fats play a very important role throughout the body.
脂肪在整个机体中起到非常重要的作用
They have a great number of health benefits and those benefits can vary by the type of
他们有很多健康益处
fat we eat.
且这些益处取决于我们所吃的脂肪种类
For example, polyunsaturated fats are precursors for hormone-like molecules called prostaglandins
例如 多不饱和脂肪是激素类分子前列腺素的前体
that stimulate endothelial cells that line blood vessels to release nitric oxide.
前列腺素刺激血管内皮细胞释放一氧化氮
Nitric oxide is a vasodilator, so that decreases resistance to blood flow and, in turn, lower
而一氧化氮是一种血管舒张剂 能降低血流阻力
blood pressure.
进而降低血压
Polyunsaturated fatty acids also help reduce the total and LDL cholesterol - and that’s
多不饱和脂肪酸也有助于降低总胆固醇和低密度脂蛋白
linked to lower rates of cardiovascular diseases like heart attacks and strokes.
这与较低的心血管疾病发病率有关 如心脏病发作和中风
Long-chain omega-3 fatty acids like DHA and EPA both help to lower plasma triglyceride
长链Ω-3脂肪酸 如DHA和EPA 都有助于降低血浆甘油三酯水平
levels which also protects against cardiovascular disease.
这也可以预防心血管疾病
Finally, DHA is important in the development of eyes and brains of young infants.
最后 DHA对婴儿的眼睛和大脑发育很重要
The impact of saturated fat on cardiovascular health is more complex.
饱和脂肪对心血管健康的影响更为复杂
Generally speaking, it’s recommended to keep consumption of saturated fat low, but
一般来讲 建议摄入较少的饱和脂肪
just like with unsaturated fats there are different types of saturated fats.
就像不饱和脂肪一样 饱和脂肪也有各种不同的类型
Evidence suggests that different types of saturated fatty acids may have different effects on our cardiovascular health.
证据表明 不同类型的饱和脂肪酸对心血管健康有不同的影响
Evidence also suggests that the health impact of reducing or replacing saturated fat in
证据还表明 减少或替代膳食中饱和脂肪对健康的影响
the diet depends on the nutrient that replaces it.
取决于对其进行替代的营养素
For example, replacing saturated fat with polyunsaturated fat has been shown to benefit cardiovascular health, whereas replacing saturated fat with refined carbohydrate has not.
例如 用多不饱和脂肪代替饱和脂肪已被证明有益于心血管健康 而用精制碳水化合物代替饱和脂肪则没有益处
Based on this, the National Academies of Medicine recommends consuming 20-35% of our daily calories
基于此 美国国家医学院建议每天摄入总能量的20-35%来自于脂肪
as fats - for a 2000 daily calorie intake, that’s between 400 and 700 calories from
-对于每日2000卡路里的摄入量来说 大约400-700的卡路里来自于脂肪
fat, or about 44 to 78 grams.
即44-78克脂肪
And it’s not just about the amount of fat we eat, the type also matters.
不仅是我们吃的脂肪总量 脂肪的类型也很重要
The World Health Organization and the US Dietary Guidelines recommend that less than 10% of
世界卫生组织和美国膳食指南建议
daily calories come from saturated fats and that trans fat consumption should be kept as low as possible.
每日饱和脂肪的摄入量应少于总热量的10% 反式脂肪的摄入应尽可能低
All right, as a quick recap: Fats are an essential part of our diet and health.
好的 快速回顾一下 脂肪是我们饮食和健康的重要组成部分
Fatty acids are either saturated or unsaturated, and foods with fat always contain a mixture of fatty acid types.
脂肪酸可以是饱和或不饱和的 而含有脂肪的食物 通常含有多种脂肪酸
Healthy diets that emphasize mono and polyunsaturated fats over saturated and trans fats are associated
健康饮食强调单不饱和脂肪和多不饱和脂肪 而非饱和脂肪酸
with lower cardiovascular disease risk.
反式脂肪会增加心血管疾病的风险
Improvements to your diet and health can be achieved by focusing more on the type of fat
改善饮食和健康
we eat and less on the amount.
需要更多的关注摄入脂肪的种类 而不只是关注脂肪摄入量
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