哈佛专家说你错了 胖并非吃太多

David Ludwig often uses an analogy when he talks about weight loss: Human beings are not toaster ovens. If we were, then the types of calories we consumed would not matter, and calorie counting would be the most effective way to lose weight. Dr. Ludwig, an obesity expert and professor of nutrition at the Harvard T.H. Chan School of Public Health, argues that weight gain begins when people eat the wrong types of food, which throws their hormones out of whack and sets off a cycle of cravings, hunger and bingeing. In his new book, “Always Hungry?,” he argues that the primary driver of obesity today is not an excess of calories per se, but an excess of high glycemic foods like sugar, refined grains and other processed carbohydrates. Recently, we caught up with Dr. Ludwig to talk about which foods act as “fertilizer for fat cells,” why he thinks the conventional wisdom on weight loss is all wrong, and long-term strategies for weight loss. Here are edited excerpts from our conversation. Q. What is the basic message of your book? A. The basic premise is that overeating doesn’t make you fat. The process of getting fat makes you overeat. It may sound radical, but there’s literally a century of science to support this point. Simply cutting back on calories as we’ve been told actually makes the situation worse. When we cut back on calories, our body responds by increasing hunger and slowing metabolism. It responds in an effort to save calories. And that makes weight loss progressively more and more difficult on a standard low calorie diet. It creates a battle between mind and metabolism that we’re doomed to lose. Q. But we’ve all been told that obesity is caused by eating too much. Is that not the case? A. We think of obesity as a state of excess, but it’s really more akin to a state of starvation. If the fat cells are storing too many calories, the brain doesn’t have access to enough to make sure that metabolism runs properly. So the brain makes us hungry in an attempt to solve that problem, and we overeat and feel better temporarily. But if the fat cells continue to take in too many calories, then we get stuck in this never-ending cycle of overeating and weight gain. The problem isn’t that there are too many calories in the fat cells, it’s that there’s too few in the bloodstream, and cutting back on calories can’t work. Q. That’s very different from the conventional wisdom that weight loss boils down to calories in, calories out. A. Yes. An analogy would be like trying to treat a fever with an ice bath. Imagine going to the hospital with a very high fever, and the doctor says, “Fever is just a problem of heat balance – too much heat in the body, not enough heat leaving the body.” That’s true from a physics standpoint. So the doctor decides to put you in an ice bath. That will work temporarily. An ice bath will break your fever. But imagine what’s going to happen. Your body is going to fight back furiously with severe shivering and blood vessel constriction and you’ll feel miserable. You’ll want out of that ice bath as soon as possible. For that reason, ice baths are not a popular treatment for fever. Q. So in this analogy, how do you treat the underlying cause? A. A much more effective approach is to lower the body’s temperature set point, which is done with medicine like aspirin. Put biology on your side by eating the right way, and weight loss occurs naturally as a fever would break if you treat the underlying cause of the fever. Q. If it’s not overeating, then what is the underlying cause of obesity? A. It’s the low fat, very high carbohydrate diet that we’ve been eating for the last 40 years, which raises levels of the hormone insulin and programs fat cells to go into calorie storage overdrive. I like to think of insulin as the ultimate fat cell fertilizer. When someone with Type 1 diabetes first comes to attention, their blood sugar is high because they can’t make enough insulin. They invariably have lost weight. They may be eating 5,000 calories a day, and they’re still losing weight. You can’t gain weight without insulin. The opposite is also true. If you give someone with diabetes too much insulin, they will inevitably gain weight. Insulin programs the body to store calories, and most of those calories get stored in the fat cells. If you’ve got too much insulin, you’re going to store too many calories. This has been very well established scientifically. Q. How do you get your obese patients to lower their insulin? A. The quickest way to lower insulin is to cut back on processed carbohydrates and to get the right balance of protein and fat in your diet. A high fat diet is really the fastest way to shift metabolism. It lowers insulin, calms fat cells down and gets people out of the cycle of hunger, craving and overeating. Q. It sounds like the program you’re advocating is the Atkins diet. A. No, this is different. The Atkins diet is a very low carbohydrate diet, which in its classic form means you can’t eat much fruit let alone any other carbohydrate. Many people don’t require – and are probably unwilling to sustain – the rigors of a very low carbohydrate diet. I think that except for people with already very severe metabolic problems like Type 2 diabetes, such restrictive regimens are not usually necessary. Q. How does this program work? A. Our program has three phases. First we tell people to give up processed carbohydrates, added sugars and all grain products for two weeks. The carbohydrates you eat should be a range of nonstarchy vegetables, fruits and beans. After two weeks, we reintroduce whole kernel grains, potatoes – except for white potatoes – and a little bit of added sugars. You do this until your weight comes down to a new, lower set point. It could be a few weeks, or it could be many months for someone who has a more significant weight problem. Q. Where do you stand on saturated fat? A. I think throughout the public health establishment we’re recognizing that saturated fat isn’t Public Health Enemy No. 1. But it’s also not necessarily a health food. There are many different kinds of saturated fats, and each of these has different effects on the body. But when you reduce processed carbohydrates and your insulin levels decrease, the saturated fat you consume burns faster and it doesn’t stick around the body as long. We have to stop thinking about saturated fat as either just good or bad. Our meal plan is based on whole natural foods, which include saturated fat. But we make sure to balance that with lots of mono- and polyunsaturated fats like olive oil, nuts, avocado and flaxseed oil. Q. Ultimately, what do you want people to take away from this book? A. Until we address the underlying drivers of weight gain – which are fat cells stuck in calorie storage overdrive – we are going to be in a battle between mind and metabolism that we just can’t win. Cutting back on calories won’t do it. That doesn’t change biology. To change biology, you have to change the kinds of foods you’re eating. 谈到减肥，戴维·路德维希(David Ludwig)经常会打这么一个比方：人体可不是个烤箱哟。如果是烤箱的话，那我们不管吃何种食物都无关紧要，而且计算热量卡路里数会是最有效的减肥方法。 路德维希博士是哈佛大学公共卫生学院(Harvard T.H. Chan School of Public Health)的肥胖症专家和营养学教授，他认为，人要是吃错了东西，就会引发激素紊乱，陷入“想吃—饥饿—暴饮暴食”的恶性循环，结果就是体重开始增加。在其新书《总觉得饿吗？》(Always Hungry?)中，他提出，如今，肥胖症的主要原因并非是摄入了过多的热量本身，而是食用了过量的高升糖指数食物，如糖、精制谷物和其他经加工的碳水化合物等。 近日，我们采访了路德维希博士，请他谈谈哪些食物是“脂肪细胞的肥料”，为什么他认为关于减肥的传统观念全是错的，以及减肥的长期策略等。以下是我们的对话节录。 问：请问你这本新书的主旨是什么？ 答：这本书的基本前提是，并非是暴饮暴食让你发胖，而是发胖的过程会令你过量进食。这听起来可能有些过激，但我们可以毫不夸张地说，最近一个世纪以来的科学足以支持这一观点。那些要我们减少热量摄入的告诫其实起了反作用。一旦热量摄入减少，我们的身体就会做出反应，一方面增加饥饿感，另一方面则减缓新陈代谢的速度。也就是说，它在尽可能地节约热量。正因为此，人们往往会发现在坚持标准的低热量饮食时，减肥变得越来越困难了。在这场意志与新陈代谢之间的斗争中，我们注定会是失败者。 问：但是，人们不是一直都在说，肥胖是因为吃得太多造成的么？难道事实并非如此？ 答：我们总觉得肥胖是一种过剩，但它实际上更近似饥饿的状态。如果脂肪细胞总是过度地储存热量，大脑就得不到足够的热量来确保新陈代谢正常运行。为了解决这个问题，大脑让我们产生了饥饿感，于是我们吃下了超量的食物，暂时感觉好过了一些。但如果脂肪细胞继续囤积过多的热量，我们就会被困在无休无止的“暴饮暴食—体重增加”的循环当中。所以问题并不在于脂肪细胞中的热量过多，而是血液中的热量太少。这就是靠减少热量摄入无法成功减肥的原因。 问：这与将减肥归结为热量收支的传统观念有很大差异呢。 答：是啊。我们可以拿“试图用冰浴退烧”来做个类比。想像一下，你因为发高烧而去医院就诊，医生跟你说：“发烧只是热平衡的问题——体内热量过多，散热不足。”从物理学的角度来看，这倒是也没错——于是医生决定让你接受冰浴。暂时看来，这当然会有效，冰浴确实能让你的体温降低。但是，请想像一下接下来会发生什么。你的身体很快会对低温环境做出反击，你剧烈颤抖，血管收缩，你觉得苦不堪言，渴望尽快从那冰浴中逃离。所以，医生根本不会把冰浴作为退烧的常用治疗手法。 问：那么，仍然借用这个类比来说，你认为应如何针对病因加以治疗呢？ 答：利用阿司匹林等药物降低体温调定点是较为有效的方法。正如你想要退烧，就要治疗发烧的根本原因一样，当你食用正确的食物时，生物学规律就会自然而然地帮你减肥。 问：如果肥胖的根本原因不是暴饮暴食，那又是什么呢？ 答：是近40年来我们的低脂肪但碳水化合物非常高的饮食，它会提高胰岛素的水平，促使脂肪细胞过度储存热量。我喜欢把胰岛素称为脂肪细胞的首要增肥剂。 当I型糖尿病刚刚出现时，病患的身体因为无法制造出足够的胰岛素，血糖总是很高。他们几乎无一例外都非常消瘦。虽然他们每天可摄入多达5000卡路里的热量，体重仍在不断地减轻。没有足够的胰岛素，你就长不胖。反之亦然。要是你给某个糖尿病患者注射了过量的胰岛素，他就会不可避免地增加体重。胰岛素促使身体存储热量，这些热量大多会以脂肪的形式储存在脂肪细胞里。如果你体内的胰岛素过多，你就会储存过多的热量。这些都已经得到了科学的充分证实。 问：那要如何才能降低肥胖症患者的胰岛素水平呢？ 答：降低胰岛素的最快办法是少吃经加工的碳水化合物，并均衡摄入蛋白质和脂肪。其实，高脂肪饮食是改变新陈代谢的最迅速的方法。它可以降低胰岛素水平，让脂肪细胞不再忙于囤积脂肪，人就摆脱了“饥饿—食欲—暴饮暴食”的怪圈。 问：这么说，你崇尚阿特金斯饮食(Atkins diet)？ 答：不，我推荐的减肥方案与之不同。阿特金斯饮食是碳水化合物含量非常低的饮食。在典型的阿特金斯饮食中，你不能吃太多的水果，更遑论其他的碳水化合物。很多人并不需要——而且很可能也不愿意维持这样严格的低碳水化合物饮食。我认为，只要你没有II型糖尿病之类非常严重的代谢问题，一般无需执行这种限制太多的治疗方案。 问：那你的治疗方案是怎样的？ 答：我们的治疗方案分为三个阶段。首先，我们要求人们在两周内完全不食用经加工的碳水化合物、添加糖和所有的谷物制品。你可以吃碳水化合物，但应该选择各种非淀粉类蔬菜、水果和豆类。两周后，你可以在膳食中添加全粒谷物、薯类（土豆除外）和一点点的添加糖。请坚持这样的饮食，直到你的体重下降到一个新的、较低的调定点上。这可能需要几个星期，对于体重问题较为严重的人甚至需要数个月的时间。 问：你对饱和脂肪怎么看？ 答：我认为，整个公共卫生界正逐渐认识到饱和脂肪并非公共健康的头号公敌——但它也未必是健康食品。饱和脂肪有很多不同的种类，每种对人体各有不同的影响。不过，当你减少经加工的碳水化合物的摄入量，胰岛素水平下降后，你燃烧摄入的饱和脂肪的速度就会加快，它就不会一直赖在你的身体里。 我们不应再单纯地考虑饱和脂肪是好是坏。我们的膳食计划的基础是全天然食品，其中包括了饱和脂肪。但必须确保我们在摄入饱和脂肪的同时，摄入大量的单不饱和脂肪和多不饱和脂肪，如橄榄油、坚果、鳄梨和亚麻籽油，让这两者之间达到均衡。 问：最后，你希望读者从这本书中学到什么？ 答：脂肪细胞过度囤积热量是我们体重增加的根本原因，如果不能解决这个问题，我们就注定要在意志与新陈代谢之间的战斗中一败涂地。减少热量摄入达不到这个目标，它不会改变你的生理状态；而要改变生理状态，你必须改变你的食物种类。昆明韦博国际英语