评论
打印
What Nearly Brainless Rodents Know About Weight Loss and Hunger
几乎无脑的啮齿动物对减肥和饥饿知道些什么
Do we really have free will when it comes to eating?
对于吃东西，我们真的有自由意志吗？
It’s a vexing question that is at the heart of why so many people find it so difficult to stick to a diet.
这是一个令人困扰的问题，也正是许多人难以坚持节食的核心原因。
To get answers, one neuroscientist, Harvey J. Grill of the University of Pennsylvania, turned to rats and asked what would happen if he removed all of their brains except their brainstems.
为了找到答案，宾夕法尼亚大学的神经科学家哈维·J. 格里尔把目光转向老鼠，并提问，如果移除它们除脑干之外的所有大脑，会发生什么？
The brainstem controls basic functions like heart rate and breathing.
脑干控制着基本功能，如心率和呼吸。
But the animals could not smell, could not see, could not remember.
但（移除大脑后的）老鼠失去了嗅觉、视觉、记忆力。
Would they know when they had consumed enough calories?
它们是否还能知道自己摄入了足够的卡路里？
Those studies, initiated decades ago, were a starting point for a body of research that has continually surprised scientists and driven home that how full animals feel has nothing to do with consciousness.
这些从几十年前开始的研究是一系列研究的起点，这些研究不断让科学家感到惊讶，并清楚表明动物的饱腹感与意识无关。
While most of the studies were in rodents, it defies belief to think that humans are somehow different, said Dr. Jeffrey Friedman, an obesity researcher at Rockefeller University in New York.
纽约洛克菲勒大学的肥胖症研究员杰弗里·弗里德曼博士表示，尽管大多数研究对象是啮齿动物，但若认为人类存在某种不同之处，这是令人难以置信的。
Humans, he said, are subject to billions of years of evolution leading to elaborate neural pathways that control when to eat and when to stop eating.
他说，人类经过数十亿年的进化，形成了复杂的神经通路，这些通路控制着何时进食以及何时停止进食。
As they have probed how eating is controlled, researchers learned that the brain is steadily getting signals that hint at how calorically dense a food is.
研究人员在探索大脑如何控制进食时发现，大脑会持续接收关于食物热量密度的信号。
There’s a certain amount of calories that the body needs, and these signals make sure the body gets them.
身体需要一定量的卡路里，这些信号确保身体获取了这些卡路里。
The process begins before a lab animal takes a single bite.
这个过程在实验动物吃第一口之前就已经开始了。
Just the sight of food spurs neurons to anticipate whether a lot of calories will be packed into that food.
只是看到食物就会刺激神经元去预测，该食物是否含有大量热量。
The neurons respond more strongly to a food like peanut butter — loaded with calories — than to a low-calorie one like mouse chow.
神经元对花生酱等高热量食物的反应比鼠粮等低热量食物更强烈。
The next control point occurs when the animal tastes the food: Neurons calculate the caloric density again from signals sent from the mouth to the brainstem.
下一个控制点出现在动物品尝食物时：神经元根据从口腔发送到脑干的信号再次计算热量密度。
Finally, when the food makes its way to the gut, a new set of signals to the brain lets the neurons again ascertain the caloric content.
最终，当食物进入肠道时，一组新的信号会传递给大脑，让神经元再次确认食物的热量含量。
And it is actually the calorie content that the gut assesses, as Zachary Knight, a neuroscientist at the University of California San Francisco, learned.
事实上，正如加州大学旧金山分校的神经科学家扎克里·奈特所发现的，肠道评估的是热量含量。
He saw this when he directly infused three types of food into the stomachs of mice.
他直接将三种食物注入老鼠胃部时看到了这一点。
One infusion was of fatty food, another of carbohydrates and the third of protein.
一种是脂肪类食物，另一种是碳水化合物，第三种是蛋白质。
Each infusion had the same number of calories.
注入的每种食物热量相同。
In each case, the message to the brain was the same: The neurons were signaling the amount of energy, in the form of calories, and not the source of the calories.
每种情况下，传递给大脑的信息都是相同的：神经元传递的是以卡路里衡量的能量数值，而非卡路里的来源。
When the brain determines enough calories were consumed, neurons send a signal to stop eating.
当大脑判定摄入的卡路里足够时，神经元就会发出停止进食的信号。
Dr. Knight said these discoveries surprised him.
奈特博士表示，这些发现令他感到惊讶。
He’d always thought that the signal to stop eating would be “a communication between the gut and the brain,” he said.
他说，他一直以为停止进食的信号会是“肠道与大脑之间的交流”。
There would be a sensation of having a full stomach and a deliberate decision to stop eating.
他以为会有一种饱腹感，然后是有意决定停止进食。
Using that reasoning, some dieters try to drink a big glass of water before a meal, or fill up on low-calorie foods, like celery.
基于这种推理，一些节食者尝试在饭前喝一大杯水，或者用低热量食物（如芹菜）填饱肚子。
But those tricks have not worked for most people because they don’t account for how the brain controls eating.
但这些办法对大多数人并不奏效，因为他们没有考虑到大脑是如何控制进食的。
In fact, Dr. Knight found that mice do not even send satiety signals to the brain when all they are getting is water.
事实上，奈特博士发现，当老鼠仅摄入水分时，它们根本不会向大脑发送饱腹信号。
