減肥難 真的 真的 真的 很難
Losing weight is hard, Like really, really, really hard.
絕大多數嘗試減肥的人
The overwhelming majority of people who try to do it
都以失敗告終或是反彈回來 有時甚至更胖
don’t succeed or end up gaining back what they lose, sometimes more.
那不僅是因為披薩太好吃了
And that’s not just because pizza is amazing.
更有事實證明 你的身體會拖後腿
It turns out your body actually pushes back
當你嘗試減肥時
when you attempt to slim down.
儲存在脂肪組織裡的脂肪
The fat stored in your adipose tissue
是一種富含能量的物質
is a super energy-rich substance
使身體能在必要時 為細胞提供能量
that your body can use in a pinch to fuel your cells.
如果你出於什麼原因不能吃東西
If you can’t eat for whatever reason,
或者你只是需要一點額外的能量來生長或繁殖
or you just need a little extra energy to grow or reproduce,
你的身體就會分解脂肪
your body can turn to your fat,
那就是為什麼從生存的角度來說
which is why from a survival perspective,
有些脂肪其實是件好事
having some fat is actually a good thing!
但是 你可能會認為減肥很簡單
Still you』d think that losing weight wouldbe pretty straightforward
只需要吃得比身體需要的少
just eat less than you need,
強迫身體消耗一些脂肪
and force your body use up some of its fat,
達到理想的體型後 再回到正常的飲食量
then go back to eating a normal amount when you’re the size you want to be.
但是身體可不想失去能量儲備
But the body doesn’t want to lose its energy buffer
無論多少
no matter how large or small it is,
所以當你減少卡路裡攝入時
so when you cut calories,
身體會做出反應 反而使你更難減肥
it reacts in ways that ultimately make it harder to lose weight.
重新長胖很多時候是由激素導致的
A lot of the push back is driven by changes to hormones.
其中最重要的是瘦素
One of the most important is leptin,
一種由脂肪細胞分泌的激素
a hormone secreted by your fat cells.
脂肪細胞越大 產生的瘦素就越多
The larger your fat cells are, the more leptin they produce.
所以當你減肥的時候 瘦素水平就會下降
So when you lose weight, leptin levels drop.
大腦中的某些部分 比如下丘腦
Parts of your brain like your hypothalamus
會把瘦素減少解讀為飢餓
interpret less leptin as starvation,
然後它會介入進來 告訴你的身體
and it jumps in and starts telling your body
要節約能量 多吃點東西 來重建能量儲備
to conserve energy and to eat more to rebuild those reserves.
其他器官也會向你的大腦抱怨
Other organs also use hormones to complain to your brain
能量攝入的減少
about the decrease in fuel intake.
胃通過提高飢餓素的指標
Stomach tells your brain it’s not getting filled
告知大腦它尚未充滿
by increasing levels of the hormone ghrelin.
同時 胰腺減少分泌可調節血糖的胰島素
At the same time, your pancreas secretes less insulin,
和可提示飽腹的胰澱素
which regulates blood sugar and amylin, which signals fullness.
所以當你減少卡路裡攝入時 胃釋放的飢餓素水平上升
So when you cut calories, ghrelin levels rise
而胰島素和胰澱素水平迅速下降
and insulin and amylin levels plummet,
這會讓你的大腦增加食慾 讓你感覺到餓了
signalling your brain to increase appetite, making you feel ravenous.
除了改變你的飢餓感之外
In addition to changing how hungry you feel,
一系列的研究表明
a suite of studies have suggested
大腦對於這些激素變化做出的反應是
your brain responds to these hormonal changes
讓你更清楚地感覺到自己沒有吃到食物
by making you more aware of all the food you’re not eating,
如果你就此放棄減肥 反而會更加愉悅
and upping the pleasure you feel if you do cave in.
同時 你身體的其他部分會變得更加節能
Meanwhile the rest of your body becomes moreenergy-efficient.
例如 肌肉會改變獲得能量的方式
For example, your muscles change where theyget their fuel.
當肌肉需要能量的時候
When your muscles need energy,
它們通常會同時消耗儲存的脂肪和循環的葡萄糖
they generally use a mix of stored fat and circulating glucose.
但是當你節食時 它們更依賴葡萄糖
But when you’re on a calorie-restricted diet, they rely more heavily on glucose,
所以它們最終會從攝入食物中獲取更多能量
so they end up pulling more energy from the foods you eat,
而不是從那些你嘗試消耗的脂肪中
instead of those fat stores you’re trying to lose.
它們還會做出其他節能調整
They also make other small changes to become more efficient,
其他身體組織也是如此
and so do other tissues in your body.
真正令人惱火的事情是
Here’s the really annoying thing:
當你停止節食時 激素釋放的飢餓信號不會停止
this hormonal starvation signal doesn’t stop when you stop dieting.
那使得瘦素水平很有意義
That makes sense for leptin,
因為它基於你所具有的脂肪量而產生
since it’s based on the amount of fat you have.
但其他激素受攝入食物影響
But other hormones which generally respond to food intake
會保持在一個較低的分泌狀態
can stay on that slower production cycle.
即使當你已經恢復正常的飲食
Even when you return to normal eating,
這些激素仍會多年保持在一個較低的分泌狀態
and these hormones can stay altered for years.
因此 即使你不再限制卡路裡攝入
So even when you』ve stopped restricting calories,
你的身體會表現得如同它依然飢餓一樣
your body continues to act as being starved.
這是減肥的人經常反彈的一個重要原因
which is a big part of why people who lose weight often gain it back.
更糟糕的是
To make matters worse,
即使重新胖回來 也不會讓你的身體擺脫節能模式
even regaining the weight doesn’t shift your body out of energy-efficient mode.
一般來說 你的體重越小
In general, the smaller you are,
你需要提供的能量越少
the less energy you need to fuel everything.
但這並不是簡單線性關係
But it’s not a simple, linear relationship.
每消耗一公斤體重所需的能量
How much energy you use per kilo at any given body weight
會根據你曾經更瘦還是更胖而變化
varies depending on whether you』ve ever been heavier or skinnier.
這個結果在2016年的一項研究中清晰可見
And this effect could be clearly seen in a 2016 study
這項研究持續六年跟蹤記錄一項電視減肥比賽的選手
which followed contestants from a televised weight loss competition for six years.
研究人員尤其關注選手的靜息代謝率
particularly the researchers looked at the participants』 resting metabolic rates,
也就是他們在休息時身體會消耗多少卡路裡
the calories their bodies burned at rest.
這基本上是人體維持細胞正常運轉的最低能量代謝量
It’s basically a measure of the minimum amount of energy needed to keep a person’s cells running.
經過三十周的比拼後
After the 30 week contest,
這14位選手平均減掉了約58千克
the 14 participants lost an average of about 58 kilograms,
他們的靜息代謝率每天下降610卡路裡
and their resting metabolic rates dropped by about610 calories per day.
然而 在跟蹤記錄的之後一年裡
In the years that followed, though,
他們體重平均回增41公斤
they gained back an average of 41 kilos,
不過靜息代謝率卻未能相應回調
and their metabolic rates didn’t go back up accordingly.
最終 他們每天消耗的熱量比最終體重時應該消耗的熱量少消耗500卡路裡
They ended up burning 500 calories a day less than they should have at their final weights.
這意味著如果未來他們想減肥
Which means to lose weight in the future,
他們必須要比第一次減肥時 更嚴格約束自己
they』d have to restrict themselves even more than they did the first time around.
很多其他的研究也得出了類似的結論
Lots of other studies have come to similar conclusions.
人們減肥之後 即使又胖了回來
After people lose weight, even if they gain it back,
他們每公斤體重消耗的卡路裡
their bodies simply use fewer calories per kilogram
比體重沒有變化的相似身材的人少
than similarly sized people whoseweight hasn’t changed.
這意味著相比從沒胖過的人他們必須吃更少
And that means they have to eat less
來保持現在的體重
to stay at that weight than people who were never heavier,
如果吃多了 他們會更容易增加體重
and they gain weight faster if theydo overeat.
現在還不清楚 這些抵抗減重的能量減耗 會持續多久
It’s not yet clear just how long all these anti-weight loss changes last
或者這個變化是否會完全消失
or if they ever completely go away.
但不同的人 身體會遇到不同程度的阻力
But not everyone experiences the same degree of resistance from their bodies.
科學家仍在嘗試弄清人體基因
Scientists are still trying to figure out how our person’s genetics,
攝入食物及其他因素 如何影響人們對節食的反應
the foods they eat, and other factors affect how a person responds to dieting.
但是考慮到身體如此強烈地阻止減肥
But given how fiercely the body can fight slimming down,
也難怪這麼多人要和減肥苦苦做鬥爭
it’s no wonder so many people struggle with it.