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.
And sometimes, it’s just too hard to resist.
And scientists have been trying to figureout why junk foods
have so much power over us for a while.
According to a study published yesterdayin the journal Cell Metabolism,
it probably has a lot to do with the fact that
they’re usually packed with both fat and carbs. Pff,
The researchers found that the reward centersof our brains
are more active when those nutrients are combinedin a snack—
above and beyond what you would expect
if you just added the fat and the carbs together.
Which is why milkshakes, and french fries,
and dipping your french fries into milkshakes.
And that means that it ’ s not
just you—junk food basically hacks our brains. Now,
there have been hints to this phenomenon forsome time. Mice,
can stay trim if they ’ re given either carbs or fat to eat,
but they pack on the pounds
if they ’ re given a mix of the two.
But it was less clear how that plays out
in the brain, or how it applies to people.
So neurologists and physiologists in Germanyand the US
set up a kind
of food auction where participants bid for snacks
while the activity in their brains was measuredwith fMRI.
The calories in the various snacks were eithermostly from carbs,
mostly from fat, or from a mix of both.
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.
The team also made sure
that all the foods were similarly well known and liked in a previous experiment.
That way, the group couldn ’ t prize any set of foods over the others.
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.
This willingness to shell out more
for the foods that had both fat and carbs
was associated with more of a response inbrain regions
associated with reward, like the top partof the striatum.
The researchers suspect this may be becausewe have
separate reward pathways for fats and carbs,
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
firing is something our brainsjust don’t know how to handle.
That actually makes sense if you look at ourancestors.
For eons, people mostly ate one food group
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.
They didn’t really have the option to do anything else
because very few foods are naturally richin carbs and fat.
Agriculture made it easier to mix nutrientgroups in meals,
but it still wasn ’ t
until the last 150 years or so that we started actually making
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,
our brains simply haven ’ t had to try to estimate the nutritional value of fatty, carb-filled foods.
The researchers also discovered that we ’ re pretty terrible at making such judgements.
When they asked the participants to guess the calories in the snacks they were bidding on,
they kinda failed when it came to the carb-y and combo foods.
The researchers even identified a part
of the brain called the fusiform gyrus—
a long strip that’s at the base of our brains—that ’ s important
for making these kinds of estimations. So,
if we can’t
estimate calories very well when carbs are involved,
and we’re getting a bigger reward from thosefat/carb combinations,
that goes a long way to explaining why
it’s so hard
for me to not eat more donuts when somebody brings donuts in to work.
I ’ m not saying I resent you for bringing the donuts in,
but it’s just hard, okay?
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,
scientists may be able to usethis information
to better understand overeating and obesity.
And hopefully, that means they
can come up with ways for people
to make better food choices,
even when they’re surrounded by lots of junk,
as we so often are.
Our next topic, weirdly enough,
is about one of those rare natural foods
that’s rich in the carb and the fat department.
African baobab trees produce fruits that have a starchy pulp and a fatty seed.
So in a way, that makes them, like,
kind of a proto-junk food,
except that they’re also packed with fiber and protein,
so they ’ re pretty healthy.
The problem is,
a new report out this week in the journal Nature Plants
found that many of the biggest and oldestbaobabs—
some of which have been feeding people forthousands of years—
are inexplicably dying out.
The international research team surveyed 60trees across the globe,
checking on their health, measuring their size,
and taking wood samples to estimate their ages.
While you might think you could just, like,
count the rings like other trees,
baobabs can grow more than one trunk throughouttheir lives.
These sometimes fuse together, creating whatlooks like one big trunk,
but inside there are open spaces.
And this complexity makes it really hard todate them—
the baobab ’ s structure is so wacky
that rings don ’ t tell you very much. So,
the scientists relied on special typeof radiocarbon dating instead.
In this method, you use a very small sample
from multiple parts of the tree,
and count the number of all the different types of carbon atoms,
which can then give you a date estimate.
The team found that many trees were more
than 1,000 years old,
including one that was nearly 2,500 years old,
making it the oldest flowering tree on theplanet. But,
in a horrible and unexpected twist, theyalso discovered that
9 of the 13 oldest trees and 5
of the 6 biggest trees were dead
or had at least one trunk that was dead.
And those deaths all happened within the last12 years.
Scientists aren’t sure why this is happening,
although they suspect climate change mightbe to blame.
With warmer temperatures and more drought,
the trees might be struggling to get enough water to support their large frames.
But further research is needed to confirmthat suspicion.
所以 现在 关键在于
So now, the race is
on to figure out exactly what ’ s going on
before we lose these iconic trees for good.
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