[音乐]
[INTRO ♪]
众所周知 垃圾食品 虽然它不健康 但是 很好吃
Junk food: you know it’s not healthy, butit’s so good.
有时候 很难拒绝它
And sometimes, it’s just too hard to resist.
科学家曾经试图弄清楚为什么垃圾食品
And scientists have been trying to figureout why junk foods
能够如此风靡一时
have so much power over us for a while.
根据《细胞代谢》杂志昨天刊登的一篇研究
According to a study published yesterdayin the journal Cell Metabolism,
这可能与
it probably has a lot to do with the fact that
垃圾食品大都包含脂肪和碳水化合物 有关
they’re usually packed with both fat and carbs. Pff,
我的最爱
my favorite!
研究者发现当脂肪和碳水化合物这两种营养素混合在一起时
The researchers found that the reward centersof our brains
大脑的奖励中心的活跃度
are more active when those nutrients are combinedin a snack—
大大超出你的期待
above and beyond what you would expect
如果你只添加脂肪和碳水化合物
if you just added the fat and the carbs together.
这就是为什么奶昔 薯条
Which is why milkshakes, and french fries,
薯条蘸奶昔会如此诱人
and dipping your french fries into milkshakes.
这就意味着
And that means that it ’ s not
垃圾食品基本上干扰了大脑 现在
just you—junk food basically hacks our brains. Now,
有一些现象可以显示
there have been hints to this phenomenon forsome time. Mice,
比如
for example,
如果只给老鼠吃碳水化合物或脂肪 老鼠就会显瘦
can stay trim if they ’ re given either carbs or fat to eat,
但是如果老鼠吃了碳水化合物和脂肪的混合物的话
but they pack on the pounds
老鼠整体重量就会增加
if they ’ re given a mix of the two.
但很难弄清楚对大脑的影响
But it was less clear how that plays out
或者说 对人的影响
in the brain, or how it applies to people.
所以德国和美国的神经病学家和生理学家
So neurologists and physiologists in Germanyand the US
建立了一种
set up a kind
参与者对零食竞标的食物拍卖
of food auction where participants bid for snacks
同时 功能磁共振成像检测参与者脑中的活动
while the activity in their brains was measuredwith fMRI.
各种零食中的卡路里大多来自碳水化合物
The calories in the various snacks were eithermostly from carbs,
脂肪 碳水化合物和脂肪的混合物
mostly from fat, or from a mix of both.
食品按大小分类 每一个种类都包含
And the items were sized so that each categorycontained
同样数量的卡路里 从能量方面来讲 所有东西都平等对待
the same number of calories, to make them equal from an energetic perspective.
实验小组也尽力确保
The team also made sure
所有的食物都是在上一次实验中我们所熟知的和喜爱的
that all the foods were similarly well known and liked in a previous experiment.
这样 就会不偏不倚
That way, the group couldn ’ t prize any set of foods over the others.
但是 参与者们都在套餐提高标价
But the participants consistently put higherbids on the combo foods—
比如 巧克力曲奇饼干 方块糖
things like chocolate chip cookies and candy bars—
而不是 像 坚果 奶酪 咸饼干这样的食物
rather than things like nuts, cheese, or crackers.
目的是为了提供更多
This willingness to shell out more
与包含脂肪和碳水化合物的食物相关的
for the foods that had both fat and carbs
大脑区域的反射
was associated with more of a response inbrain regions
或奖励 终脑皮层的顶部
associated with reward, like the top partof the striatum.
研究者怀疑这也许是因为
The researchers suspect this may be becausewe have
脂肪和碳水化合物的不同奖励方式
separate reward pathways for fats and carbs,
结合物食物同时表现有不同奖励方式
both of which are simultaneously turned onby the combo foods.
研究者认为这 就像是 同时奖励电路
And they think this, like, simultaneous reward circuit
大脑如火中烧 只是不知道该如何处理而已
firing is something our brainsjust don’t know how to handle.
如果以我们的祖先为例 这也确实行得通
That actually makes sense if you look at ourancestors.
远古时期 人们每次大都吃一种食物组
For eons, people mostly ate one food group
当条件允许的时候
at a time, like when it became available—
一天吃肥肉食物 下一天 吃甜蜂蜜 或浆果食物
fatty meat one day, sugary honey or berries the next.
他们确实没有太多的其他的选择
They didn’t really have the option to do anything else
因为几乎没有食物是包含大量碳水化合物和水
because very few foods are naturally richin carbs and fat.
农业使得营养组合混合在食物中变得更加容易
Agriculture made it easier to mix nutrientgroups in meals,
但是
but it still wasn ’ t
直到150年前 我们开始真正制作
until the last 150 years or so that we started actually making
包含具有更多卡路里的所有营养物质的单一食品名目
single food items that contain a dozen or more calories of each nutrient type.
所以 对于 绝大部分进化历史
So for the vast majority of our evolutionary history,
我们的大脑 不需要努力地评估包含碳水和脂肪食物的营养价值
our brains simply haven ’ t had to try to estimate the nutritional value of fatty, carb-filled foods.
研究者也发现 人们并不擅长做这种判断
The researchers also discovered that we ’ re pretty terrible at making such judgements.
当他们要求参与者去判断参与者所竞标的在零食中的种类
When they asked the participants to guess the calories in the snacks they were bidding on,
当涉及到碳水类食物和组合食物 参与者并不能给出答案
they kinda failed when it came to the carb-y and combo foods.
研究者甚至可以把一部分大脑区分为
The researchers even identified a part
梭状回
of the brain called the fusiform gyrus—
一个基于大脑的重要的长条区
a long strip that’s at the base of our brains—that ’ s important
用来做出各种判断 所以
for making these kinds of estimations. So,
如果我们不能
if we can’t
在涉及到碳水时 评估分类
estimate calories very well when carbs are involved,
我们会从脂肪碳水组合物中得到更大的奖励
and we’re getting a bigger reward from thosefat/carb combinations,
需要花费更多去解释为什么
that goes a long way to explaining why
会如此困难
it’s so hard
当我们携带甜甜圈作为食物 而我们不能吃太多甜甜圈
for me to not eat more donuts when somebody brings donuts in to work.
我的意思不是你不能携带甜甜圈 把它当食物
I ’ m not saying I resent you for bringing the donuts in,
但是 就是要少吃
but it’s just hard, okay?
甜甜圈很好吃
They’re so good!
即使不好吃 我也要一直吃 最终
Even when they’re not that good I keep eating them. Eventually,
科学家可能用这些信息
scientists may be able to usethis information
更好地解释吃得过多和肥胖
to better understand overeating and obesity.
幸运地是 这意味着
And hopefully, that means they
他们能想出
can come up with ways for people
让人们做更好食物选择的方法
to make better food choices,
即使他们被垃圾食品所环绕
even when they’re surrounded by lots of junk,
正如我们经常吃垃圾食品一样
as we so often are.
我们下一个主题 更古怪
Our next topic, weirdly enough,
是关于众多稀有天然食物的一种
is about one of those rare natural foods
这种食物包含丰富的碳水化合物和脂肪
that’s rich in the carb and the fat department.
非洲猴面包树能生产一种包括含淀粉的果肉和含大量脂肪的果核的水果
African baobab trees produce fruits that have a starchy pulp and a fatty seed.
这样
So in a way, that makes them, like,
这就像是一种原始的垃圾食品
kind of a proto-junk food,
除此以外 它们还包含纤维和蛋白质
except that they’re also packed with fiber and protein,
所以这种水果也十分健康
so they ’ re pretty healthy.
问题是
The problem is,
《天然植物》杂志这周发表了一篇文章
a new report out this week in the journal Nature Plants
文章指出 很多最大的年龄最大的猴面包树
found that many of the biggest and oldestbaobabs—
已经养活人们超过一千多年了
some of which have been feeding people forthousands of years—
这些树正在莫名其妙地消亡
are inexplicably dying out.
国际研究对于调查了全球60棵树
The international research team surveyed 60trees across the globe,
检测他们的健康程度 和他们的体积
checking on their health, measuring their size,
提取木头样品来评估他们的树龄
and taking wood samples to estimate their ages.
你也可能觉得你可以
While you might think you could just, like,
像判断其他树的树龄一样 通过计算树的年伦来评估树龄
count the rings like other trees,
猴面包树一生可以生长超出树干的年伦
baobabs can grow more than one trunk throughouttheir lives.
这样 有时会创造出一种看起来是一个大的树干
These sometimes fuse together, creating whatlooks like one big trunk,
但是中部是空白的假象
but inside there are open spaces.
这种复杂确实很难去判断他们的树龄
And this complexity makes it really hard todate them—
猴面包树的结构很古怪
the baobab ’ s structure is so wacky
树龄并不能说明什么 所以
that rings don ’ t tell you very much. So,
科学家依靠特殊的放射性碳来记录日期
the scientists relied on special typeof radiocarbon dating instead.
这种方法 使用很少部分的样品
In this method, you use a very small sample
从大量的树中
from multiple parts of the tree,
计算所有种类碳原子的数量
and count the number of all the different types of carbon atoms,
你就能得到一个日期评估结果
which can then give you a date estimate.
队伍发现很多树
The team found that many trees were more
超过了一千年
than 1,000 years old,
其中有一棵树几乎有2500 的树龄
including one that was nearly 2,500 years old,
这个星球上最古老的开花的树 但是
making it the oldest flowering tree on theplanet. But,
在一个可怕未预期的扭曲中 他们也发现
in a horrible and unexpected twist, theyalso discovered that
13棵最古老树中有9棵
9 of the 13 oldest trees and 5
6棵最大的树中有5棵 已经死了
of the 6 biggest trees were dead
活着之前一个树干已经死亡
or had at least one trunk that was dead.
死亡发生在上一个12年之内
And those deaths all happened within the last12 years.
科学家不能解释这是为什么
Scientists aren’t sure why this is happening,
虽然他们觉得天气变化是主要原因
although they suspect climate change mightbe to blame.
越来越高的温度 和越来越多的干旱
With warmer temperatures and more drought,
树极力争取足够的水分来支撑他们庞大的框架
the trees might be struggling to get enough water to support their large frames.
但是 需要进一步研究来确认这一怀疑
But further research is needed to confirmthat suspicion.
所以 现在 关键在于
So now, the race is
弄清楚到底发生了什么
on to figure out exactly what ’ s going on
在我们频道永远消失之前
before we lose these iconic trees for good.
谢谢收看科学秀的本期视频
Thanks for watching this episode of SciShow!
如果你想继续了解
If you want to keep learning
我们生活的这个古怪的世界
about this wacky world we live in,
包括实时观看最新信息
including staying up to date with all the new,
令人振奋的科学研究
exciting scientific research,
请前往油管科学秀网站观看我们的视频
you might want to head on over to YouTube.com/SciShow
观看一系列相关视频 并点击浏览按键
to watch a bunch of episodes and also click on that subscribe button.
谢谢
Thanks!
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