碳水化合物为什么让你吃完更想吃？

How Carbs Can Trigger Food Cravings
By ANAHAD O'CONNOR August 02, 2013
营养
碳水化合物为什么让你吃完更想吃？
ANAHAD O'CONNOR 2013年08月02日
Are all calories created equal? A new study suggests that in at least one important way, they may not be.
各种食物产生的热量卡路里对人体的效应是否相同？一项新研究表明，它们至少在某一重要方面存在差异。
Sugary foods and drinks, white bread and other processed carbohydrates that are known to cause abrupt spikes and falls in blood sugar appear to stimulate parts of the brain involved in hunger, craving and reward, the new research shows. The findings, [要查看本链接请先注册并登录], suggest that these so-called high-glycemic foods influence the brain in a way that might drive some people to overeat.
人们已经知道，含糖的食物和饮料、白面包和其他加工的碳水化合物可引起血糖的骤然升降。而这项新研究显示，上述食物可刺激脑中与饥饿、渴求和奖励有关的区域。该研究[要查看本链接请先注册并登录](The American Journal of Clinical Nutrition)上，其结果表明，所谓的高血糖指数食物可通过某种方式对脑部造成影响，从而促使一些人过量饮食。
For those who are particularly susceptible to these effects, avoiding refined carbohydrates might reduce urges and potentially help control weight, said Dr. David Ludwig, the lead author of the study and the director of the New Balance Foundation Obesity Prevention Center at [要查看本链接请先注册并登录].
该研究的主要作者，[要查看本链接请先注册并登录](Boston Children’s Hospital)新百伦基金会肥胖防治中心(New Balance Foundation Obesity Prevention Center)的主任戴维·路德维格(David Ludwig)博士表示，对于那些对上述效应特别易感的人来说，避免食用精制的碳水化合物可降低进食冲动，并可能有助于控制体重。

“This research suggests that based on their effects on brain metabolism, all calories are not alike,” he said. “Not everybody who eats processed carbohydrates develops uncontrollable food cravings. But for the person who has been struggling with weight in our modern food environment and unable to control their cravings, limiting refined carbohydrate may be a logical first step.”
“该研究表明，就其对脑部代谢的效应而言，各种食物中的热量卡路里不尽相同，”他说，“并非所有食用加工碳水化合物的人都会出现无法遏制的食欲。然而，对于那些在现代饮食环境中试图减肥但无法控制食欲的人们，限制精制碳水化合物可能是合乎逻辑的第一步。”
Regardless of the diet they choose, most people who lose a great deal of weight have a difficult time keeping it off for good. For many people, despite their best efforts, the weight returns within six months to a year. But a few studies of weight loss maintenance, including a large one in [要查看本链接请先注册并登录], have reported some success with [要查看本链接请先注册并登录] like bagels, white rice, juice and soda.
无论选择怎样的饮食，大多数成功大幅减肥的人都觉得效果难以长久保持。虽然已尽了最大努力，很多人的体重仍在六个月至一年之内恢复原样。但也有少数研究表明，某些人通过[要查看本链接请先注册并登录]，如面包圈、白米饭、果汁和汽水等，成功地维持了减肥效果，其中包括一项[要查看本链接请先注册并登录](The New England Journal of Medicine)上的大型研究。
In addition to raising blood sugar, foods that are sugary and highly caloric elicit pronounced responses in distinct areas of the brain involved in reward. [要查看本链接请先注册并登录], for example, that the main reward and pleasure center, the nucleus accumbens, lights up more intensely for a slice of chocolate cake than for blander foods like vegetables, and [要查看本链接请先注册并登录] in the brains of obese people than it is in those who are lean.
含糖和高热量的食物除了可升高血糖之外，还可在参与奖励的特定脑区中引起明显的反应。例如，[要查看本链接请先注册并登录]，食用一块巧克力蛋糕时，脑部主要的奖励和愉悦中心伏隔核在影像上的亮度要大大高于食用蔬菜等清淡的食物，且与体态纤细的人相比，这种激活效应[要查看本链接请先注册并登录]。
But do rich desserts have a select ability to change our longer-term eating habits?
但是，口味丰腴的甜点是否造成了一种选择力，以至改变了我们的长期饮食习惯？
To get a better idea, Dr. Ludwig and his colleagues recruited a dozen obese men and then fed them milkshakes on two different occasions separated by several weeks. In each case, the milkshakes were nearly identical: flavored with milk and vanilla, and containing the same amount of calories, carbohydrates, protein and fat.
为了更好地认识这个问题，路德维格博士和他的同事们招募了十余名肥胖的男性，并在相隔数周的两个不同场合让他们食用奶昔。这两种奶昔几乎一模一样：均为牛奶与香草口味，并含有等量的热量、碳水化合物、蛋白质和脂肪。
But on one occasion, the shakes were made with high-glycemic corn syrup; on the other, a source of low-glycemic carbohydrates was used. “These test meals were identical in appearance and tastiness, and we verified that our subjects had no preference for one or the other,” Dr. Ludwig said.
不过，其中一种奶昔由具有高血糖指数的玉米糖浆制成，而另一种则使用了具有低血糖指数的碳水化合物。“这些试验餐的外观和滋味完全相同，且我们已确证，受试者对这两种奶昔中的某一种并无特殊偏好，”路德维格博士说。
As expected, blood sugar levels rose more quickly in response to the high-glycemic milkshake. But the researchers were especially interested in what happened several hours later, about the time most people are ready for their next meal.
正如研究人员预期的那样，在高血糖指数奶昔的作用下，受试者血糖水平上升更加迅速。但是，研究人员对几个小时后，大多数人准备下一次进餐时的情况更感兴趣。
What they found was that four hours after drinking the high-glycemic shake, blood sugar levels had plummeted into the hypoglycemic range, the subjects reported more hunger, and brain scans showed greater activation in parts of the brain that regulate cravings, reward and addictive behaviors. Although the subject pool was small, every subject showed the same response, and the differences in blood flow to these regions of the brain between the two conditions “was quite substantial,” Dr. Ludwig said.
他们发现，在饮用高血糖指数奶昔四小时后，受试者的血糖水平已经直线降至低血糖范围，他们自称感觉更为饥饿，脑部扫描也显示，在调控渴求、奖励和成瘾行为的脑区中出现了更大程度的激活。虽然该受试者群体较小，但每名受试者都显示了同样的反应，且在这两种情况下，流入上述脑区的血液量差异也“相当可观”，路德维格博士指出。
“Based on the strength and consistency of the response,” he added, “the likelihood that this was due to chance was less than one in a thousand.”
“基于这些反应的强度和一致性，”他补充道，“其由偶然所导致的可能性不到千分之一。”
Previous research suggests that when blood sugar levels plummet, people have a tendency to seek out foods that can restore it quickly, and this may set up a cycle of overeating driven by high-glycemic foods, Dr. Ludwig said. “It makes sense that the brain would direct us to foods that would rescue blood sugar,” he said. “That’s a normal protective mechanism.”
路德维格博士表示，既往研究表明，当血糖水平直线下降时，人们倾向于寻求能够迅速恢复血糖水平的食物，这就可能建立一种由高血糖指数食物驱动的饮食过量周期。“大脑会指示我们食用可将血糖拉回正常水平的食物这一点合情合理，”他说，“这是一种正常的保护机制。”
Christopher Gardner, a nutrition scientist at Stanford University who was not involved in the new study, said that after decades of research but little success in fighting obesity, “it has been disappointing that the message being communicated to the American public has been boiled down to ‘eat less and exercise more.’”
斯坦福大学(Stanford University)的营养科学家克里斯托弗·加德纳(Christopher Gardner)并未参与这项新研究，但他指出，我们已在抗击肥胖这个课题上进行了数十年的研究，却收效甚微，“科学界传达给美国公众的信息简而言之就只有五个字：‘少吃多锻炼’，这真令人失望。”
“An underlying assumption of the ‘eat less’ portion of that message has been ‘a calorie is a calorie,’” he said. But the new research “sheds light on the strong plausibility that it isn’t just the amount of food we are eating, but also the type.”
“其中‘少吃’这部分基于一个基本的假设，即‘不同食物中包含的热量卡路里对人体造成的效应均相同，’”他说。但这项新研究“揭示出问题的症结很可能不仅在于我们的食量，还在于食物的类型”。
Dr. Gardner said it was clear that the conventional approach of the past few decades was not working. A more helpful message than “eat less,” he said, may be “eat less refined carbohydrates and more whole foods.”
加德纳博士认为，很显然，过去几十年的传统方法行不通，并补充道，“少吃精制碳水化合物，多吃天然食品”比单纯强调“少吃”更为有益。