Some people say it's a necessary and nutritious food, vital for healthy bones,

有些人說，它是必要且營養的食物

but others say it can cause cancer and lead to an early death.

對我們的骨骼至關重要

So, who's right?

另一些人，它可能造成癌症，導致早年死亡

And why are we drinking it anyway?

究竟誰是正確的？

[Intro music]

而為什麼我們又要喝它呢？

Milk is the basis of every mammal's diet after birth,

乳類是每個哺乳類生物出生後所必需的營養

when our digestive systems are immature and small.

當我們的消化系統尚未發育而較小

Basically, it's power food to kick-start our bodies and help us grow.

基本上來說，是個充滿能量使我們快速生長的食物

Milk is rich in fat, vitamins, minerals, and milk-sugar: lactose.

並且幫助我們成長

On top of that, for a while after birth, it also contains antibodies and proteins

母乳富含脂肪、維他命、礦物質

that protect us from infections and regulate our immune system.

以及奶類中糖——乳糖

But it's a lot of effort for mothers to produce.

更重要的事，對於剛出生的小孩

Eventually, humans stop drinking mother's milk

它也含有抗體和蛋白質

and transition to the diet of their parents.

以增強我們的抵抗力，並調節我們的免疫系統

This is how it's been for thousands of years.

但生產母奶對母親的消耗極大

Until about eleven thousand years ago,

最終，當人類不再飲料母奶

when our ancestors settled down in the first agricultural communities.

變會漸漸開始轉變為其父母的飲食習慣

Soon, they domesticated the first dairy animals:

數千年來一直是如此

goats, sheep, and cattle.

直到大約1萬1千年前

They found that dairy animals are able to eat useless and abundant stuff

我們的祖先進入了農業時代

and turn it into nutritious and tasty food.

並且馴化了第一批產乳的動物

This made a huge difference in terms of survival,

山羊、綿長和牛

especially in hard times.

他們發現產乳動物會透過食用大量對人無用的東西

So groups that had milk available had an evolutionary advantage.

藉此生產營養又好吃的食物

And through natural selection,

這對生存產生極大的改變

it changed the genes of communities who consumed a lot of it.

特別是在環境惡劣時

This adaptation has to do with a specialized enzyme: lactase.

因此擁有奶類的團體得到了演化上的優勢

Babies have a lot of it in their system,

透過天擇

so they can break down the milk-sugar lactose and digest milk easily.

轉變了飲用大量奶類團體的基因

But the older we grow, the fewer lactase enzymes our body produces.

這樣的適應過程與某個酵素息息相關——乳糖酶

Worldwide, about 65% of the population do not have the enzyme after infancy,

嬰兒的消化系統擁有大量這些酵素

which means they are not able to digest more than about 150 milliliters each day.

因此他們可以分解乳糖並輕易消化奶類

This lactose intolerance is not spread evenly around the world, though.

但當我們長大，身體生產的乳糖酶也逐漸減少

In some East Asian communities, for example, it's up to 90%.

世界上有大約百分之65的人

In Northern Europe and North America, the rates are the lowest overall.

在嬰兒階段後就沒有對應的酵素

There are probably a few reasons for this uneven distribution.

這代表他們無法消化

The trait was first introduced by random mutation,

每日多於150毫升的奶類

which happened independently of each other in a few populations.

乳糖不耐的狀態並沒有平均的出現在世界上

The fact that farming replaced hunting and gathering more and more

舉例來說某些東亞國家

created natural-selection pressure.

大約是百分之九十

People who were able to digest lactose had more foods at hand,

在歐洲北方和北美比例則最低

which was an advantage.

這樣分散的狀態可能有幾個原因

The migration of dairy farmers to the north then spread it further, which probably pushed back populations there that didn't have the trait.

這樣的特徵是因為隨機的突變引起

Okay, but if milk has been a valuable part of our diet for thousands of years, why is it so controversial?

發生幾個民族中的隨機個體

There are a number of claims regarding the negative and positive health effects of milk.

當越來越農業取代採集和狩獵

The negative ones cover a wide variety,

引發了天擇的壓力

from brittle bones to cancer, and cardiovascular diseases to intolerance and allergies.

那些可以消化乳糖的人

So, how do they hold up?

得以持有更多食物

Some older studies found a connection between milk and a high risk of breast, colon, and prostate cancer

成為一種優勢

But meta analyses found no impact on your cancer risk.

畜牧業者逐漸向北擴散的遷移

On the contrary, the calcium in milk might even have a protective effect against colon cancer.

可能也擠壓了當地沒有此特徵的人口

Although this could be calcium in general, it's not clear milk plays a role in this effect.

好，那如果乳類是我們數千年的飲食習慣

Only studies on prostate cancer showed an increased risk for people who consumed more than one and a quarter liters of milk a day.

為何又會引起爭議？

But again, the association is inconsistent and other studies don't find any effects.

有許多不同的說法

We discuss these studies in more detail in our sources document. All in all, the research seems to show that if you drink between

在討論關於乳類的優缺點

100 to 250 milliliters of milk per day, cancer is not a concern.

負面的說法包含了大量不同的可能性

Similarly, meta-analyses could not find any impact from milk or dairy products on

從骨質脆化到癌症

your risk of heart disease, stroke, or your total mortality.

或從心血管疾病到過敏問題

Some studies even suggested that high blood pressure might be rarer in people who eat a lot of dairy,

他們是如何被論證？

although the evidence is not strong enough to claim this with confidence.

一些較早的研究發現

The case gets more complicated though when we look at bones.

關於乳類對乳癌、大腸癌及攝護腺癌的連結

A number of studies found neither positive nor negative effects for adults.

但許多整合分析並未發現任何影響癌症的可能性

What most people worry most about though are harmful amounts of pesticides, antibiotics, or hormones.

反而，乳類的鈣

There are hormones in milk, but only in very low concentrations.

可能還會保護身體發生大腸癌的可能性

For example to get the same amount of hormones as from the pill,

當然也可能只是鈣元素的影響

you'd need to drink about 5000 litres of milk,

和乳類本身的關係還不清楚

and even if you did, most hormones would be destroyed by your digestive system

只有關於攝護腺癌的研究發現

before they could affect you,

對於每日食用多於1.25公升乳類的人，罹癌機率增加

which is the reason why so much medication is coated to protect it from our digestion.

不過，這些關聯性依舊不明確

For pesticides and antibiotics,

而其他研究也沒有發現任何影響

there are regulations in most parts of the world that only allow completely harmless amounts.

我們可以更深入的討論

Milk that surpasses these thresholds is not allowed to go on the shelf.

在我們的資料來源的文件

So there's nothing in particular to worry about.

總而言之，這些研究似乎指出

Besides allergies and those suffering from lactose intolerances,

如果你每天喝大約100到250毫升的牛奶

the best known negative effects of milk are probably acne and general discomfort after drinking milk or eating dairy products,

癌症並不需要擔憂

and here the effects are very real.

同時，整合分析並未發現任何奶類或乳製品的影響

For example, skimmed milk has been found to statistically increase the rate of acne by 24%.

對於心血管疾病、中風或或導致死亡

Allergies against milk products are especially prevalent among children, with one in 18 kids in Germany suffering from them.

某些研究甚至指出

In general, these allergies tend to get better or disappear as they grow older though.

高血壓發生在食用更多乳製品的人上的機率更低

Okay. Is milk healthy then?

雖然證據仍未足夠明確證明這些說法

Milk, no matter if it comes from mothers, cows, sheep, goats, or camels is a nutrient-dense food.

這些狀況將變得更複雜

It contains all necessary macronutrients and many micronutrients.

當我們開始討論骨頭

Especially in regions where people struggle to get enough calories,

許多研究並未發現對成人正面或負面的影響

milk can contribute to a healthy life and lower child mortality.

許多人感到特別憂慮的地方是

For those living in the developed world, in general

有害數量的農業、抗生素或賀爾蒙

milk is not harmful if you are not allergic or intolerant to it.

奶類中的確有賀爾蒙

Especially for children, it's a good way to get large amounts of calcium

但只存在非常小的密度

and for vegetarians, it's a good source of vitamin b12 and B vitamins in general.

舉例來說，若要得到等同藥丸數量的賀爾蒙

This does not mean there are not other alternatives with the same effect. You do not need to drink milk to be healthy

你需要引用5000公升左右的牛奶

Milk is also definitely not a substitute for water.

就算你如此做到

Milk is power food, and the additional calories from drinking a lot of it on a regular basis can contribute to being overweight.

大部分賀爾蒙會被你的消化系統摧毀

Especially flavored milk or chocolate milk is more comparable to beverages like lemonade than a healthy snack, and there's another thing to consider.

在他們有可能影響你之前

Milk production has a significant impact on the global climate.

這也是為什麼許多藥丸需要保護膜

About 33 percent of cropland is used to feed grazing animals including dairy cattle

為了從我們的消化過程中保護它

Even though the carbon footprint of dairy products has declined since 1990,

而農業和抗生素

Dairy production is still responsible for 3 percent of all greenhouse gas emissions,

在世界大部分國家也會進行檢驗

even more than all airplanes combined.

只允許無害的數量

Milk is a huge industry and sadly, most of its production in factory farms causes incredible suffering.

超過閾值的牛奶

Cows are impregnated over and over, separated from their young shortly after birth,

並不允許被上架

and slaughtered once their tortured bodies are not productive anymore.

因此並沒有特別的地方需要擔心

We can't ignore that much of the milk we consume stems from an industry

除了過敏體質和乳糖不耐症

that is basically torture and contributes to climate change.

最為人所知的牛奶壞處

What about plant-based milk?

大概是青春痘和不舒適

In terms of protein levels and nutritional value, only soy milk can compare to cow milk.

在喝完牛奶或食用乳製品之後

The others need to be artificially enriched to reach similar levels of vitamins and calcium.

而這在，影響則十分明顯

So they can be an alternative to milk.

舉例來說，脫脂牛奶在數據上會提高發生青春痘的機率

And another option might be available soon.

在大約百分之24

Several startups have created non-animal milk

兒童的牛奶過敏反應也十分廣泛

that is nutritionally identical to dairy milk,

在德國每十八個兒童就有一位對此過敏

for example, through fermentation by gene modified bacteria.

大致上來說，這些過敏會逐漸轉好或消失

This lab-grown milk can even be turned into cheese,

在他們長大之後

something that plant based alternatives struggle with because they lack casein and whey protein,

好，那奶類真的健康嗎？

the key ingredients that give dairy its taste and structure.

奶類，無論從母親、乳牛、羊或駱駝

The environmental impact is a different story though.

是高營養價值的食品

Many milk alternatives use significantly less energy, land and less water to produce

它包含所有人體必要維生素，

so they have a much lower environmental impact than animal milk.

和其他維生素

If you want to have the lowest possible negative impact on the planet, the best choice is whatever milk alternative is regional.

特別是在缺乏卡路里攝取的地方

As with almost any topic milk is complicated.

奶類對健康身體是有幫助的

It's not harmful for the majority of the population and it's crucial for many people around the world.

和較低的孩童死亡率

It's good, nutritious food, but also harmful to the planet and causes a lot of suffering.

對於已開發國家，牛奶並不有害

We need to decide as a society how we want to deal with these facts.

如果你並沒有過敏或乳糖不耐的症狀

If you feel like watching more documentary style videos now, check out CuriosityStream.

特別是對孩童，是一種攝取鈣質的方式

A subscription streaming service with thousands of documentaries and non-fiction titles and sponsor of this video.

而對於素食者

With a CuriosityStream subscription,

這個好的維他命B12來源

you also get Nebula for free a streaming service owned and operated by

以及其他維他命B

education content creators like CGP Grey, Lindsay Ellis or Knowing Better.

但這不代表並沒有其他同樣效果的選擇

A place to experiment, where creators are safe from the fun things YouTube throws at us from time to time.

你不需要喝奶類才能變得健康

And, there are also originals like TierZoo's Let's Play Outside,

奶類同時也不是水的替代品

a fun video remix of a popular curiosity stream documentary!

奶類是富有能量的食品

Nebula is included with CuriosityStream for our viewers when you sign up at:

而平日因奶類而攝取的額外卡路里

So summarizing;

可能導致體重過重

CuriosityStream gives you access to big-budget documentaries from people like David Attenborough and Stephen Hawking.

特別是調味乳、巧克力奶對比其他飲料

Nebula is all about independent creators taking control and try new stuff. You get the best of both worlds

如同檸檬汁對比較健康的零食

for $2.99 per month or only $19.99 for a full year, by visiting:

也有其他方面需要注意

curiositystream.com/kurzgesagt

乳製品對於全球氣候有明顯影響

[Outro music]

大約33%的可種植土地被用於畜牧業