生物与医学2011ncbi.nlm.nih.gov
“一卡路里就是一卡路里”违反热力学第二定律
"A calorie is a calorie" violates the second law of thermodynamics
进阶 · 约 20 分钟读完前置知识：基础热力学、代谢生理学、宏量营养素
导读
这篇论文讨论为何“一卡就是一卡”的简化说法在严格意义上不成立：食物在体内转化为可用功或储存脂肪时，会因代谢途径不同而以热的形式损失能量，因此不同宏量营养素提供的净能量并不完全相同。不过评论指出，这种差异对总能量平衡的影响有限，实际减重中热量摄入与消耗仍是最主要的框架。
HN 关注点：是否真的推翻“热量收支”模型，以及减重建议应坚持简单原理还是被营养细节复杂化。
HN 评论精选
这几条评论里：质疑 2 补充 2
补充不同宏量营养素的代谢转化效率不同，蛋白质产热损失最大。
简版：脂肪、蛋白质和碳水化合物从理论热量值转化为身体有用功的效率不同。脂肪效率最高，仅损失约2-3%；碳水6-8%；蛋白质25-30%。这些损失大部分以热的形式散失。评论没有解释为什么这部分多余热量不会通过身体减少维持体温的正常过程来抵消；推测在室温下身体作为副产物产生的热量已经足够，因此没有可削减的产热过程来利用这些废热。
apinstein查看英文原文
tl;dr version: Calories derived from fat vs protein vs carbohydrates have different inefficiencies in converting them from their theoretical caloric value to their useful work in the body. Fat is the most efficient with a loss of just @ 2-3%, carbs are at 6-8%, protein 25-30%. [edit Most of] this loss is in the form of heat. It was not mentioned why this excess heat would not simply be offset by the body avoiding the normal processes it takes to maintain body temperature. Presumably the body generates enough heat as a by-product at room temperature and thus there is nothing the body can back off of to make use of the waste heat described above.
补充论文说明代谢产热造成差异，但影响很小，实践上仍支持CICO。
到目前为止大多数评论都未抓住重点。论文指出，食物可用于做功、合成脂肪或其他过程的能量，不可能等于食物本身的能量含量：它会被产热作用减少。因为不同食物的反应路径不同，例如一卡蛋白质提供的可用能量就不同于一卡脂质，更大比例的蛋白质热量变成了废热。不过从论文图2可以看出，即使大幅改变膳食构成，对食物可用能量的影响也很小。你可以大幅减少碳水摄入，同时保持2000卡摄入，但可用能量只减少约100卡。结论：在合理精度内，确实还是CICO（热量摄入对消耗）。要减重，就少吃。
leephillips查看英文原文
Most of the comments so far are missing the point. The paper points out that the energy available from food, for doing work, creating fat, or any other process, is not, and can not be, equal to the energy content of the food: it is reduced by thermogenesis. Because the reaction pathways are different for different types of food, a calorie of protein does not provide the same usable amount of energy as a calorie of lipid, for example. A greater portion of the protein calorie goes to waste heat. However, from their Figure 2, you can see that the effect of even large changes in dietary composition have a small effect on the energy available from food. You can drastically reduce your carbohydrate consumption, while maintaining your 2000 calorie intake, and that amounts to only about a 100 calorie reduction in available energy. The conclusion: to a reasonable degree of accuracy it really is CICO. To lose weight, eat fewer calories.
质疑质疑燃料类比，并把问题转向成瘾和长期行为动机。
汽车/燃料的类比很糟糕。高标号燃料只有在发动机设计能利用其特性达到更高效率（例如更高压缩比）时才有意义；否则你只是以同样效率烧更贵的燃料。不过，我真正感兴趣的是成瘾背后的机制。为什么吸烟者明知会早死还要吸烟？为什么肥胖者明知会导致严重健康问题还要暴食？底线是我倾向于同意那些认为“一卡就是一卡”、单纯减少进食对大多数肥胖者已经够用的人，尽管这在科学上可能不完全正确。但他们为什么做不到？是什么让它如此有吸引力，以至于他们忽视严重的长期劣势，有时甚至否认这些劣势的存在，尽管他们实际上一定知道那是真的。
jvdongen查看英文原文
The car/fuel analogy is a bad one. High-test fuel only makes sense if the engine in which you intend to burn it is designed to actually make use of its qualities to reach higher efficiencies (e.g. a higher compression ratio). If not, you're just burning more expensive fuel at the same efficiency. That said, what really interests me is the mechanisms behind addictions. Why do smokers smoke, knowing full well by now that it will kill them earlier than non-smokers? Why stuff obese people themselves, knowing full well that it will cause serious health issues down the line. Bottom-line I tend to agree with those who hold that 'a calorie is a calorie' and simply cutting down on food intake is a good enough principle, though perhaps not entirely scientifically correct, for the majority of obese people. But why don't they do it? What makes it so attractive that they simply ignore the serious long-term disadvantages - and even in some cases deny the existence of said disadvantages even though in reality they must know they are real.
质疑有效减重应保持简单，按TDEE控制热量，不必因营养差异把方案复杂化。
周围讨论是个有趣的假设。问题在于，人们用“并非所有卡路里都一样”这类未定科学来改变生活方式（比如“全X饮食”），然后因为把事情搞得太复杂而无法做出实质性改变。相信“一卡就是一卡”即便技术上不准确，你也可以做得很好；相信“并非所有卡路里都一样”即便在某种层面上是真的，你也可能做得很糟。有效减重很简单（注意我没说容易）：计算TDEE=((RMR+TEF+NEAT)*体力活动水平)；摄入低于TDEE减脂，高于则增脂。多数人久坐或中度活动，很多人高估自己的PAL一级。运动是为了改善整体健康，不要重复计算运动消耗，设定PAL即可。男性/女性不要低于1500/1300卡，并获取一些营养。忽略其他一切，那只是增加复杂性。减重应“简单但难”，“复杂但容易”不存在，至少中长期不存在。所以KISS，让它无聊，让它成为习惯。
Someone1234查看英文原文
The surrounding discussion is an interesting hypothetical. The problem occurs when people use unsettled science like "not all calories are created equal" to change their lifestyle (e.g. "all X diet"), then fail at making substantial change because they made it too complicated. You can do very well believing "a calorie is a calorie" even if it is technically inaccurate, and you can do very badly believing "not all calories are created equal" even if it is technically true on some level. Effective weight loss is simple (note I didn't say "easy"): - Calculate your TDEE. TDEE is ((RMR + TEF + NEAT) * Physical Activity Level). - Eat fewer calories than your TDEE in order to lose body fat or eat more to gain body fat. - Most of the population are Sedentary or Moderately active. Many also overestimate their PAL by one level (i.e. you aren't "Vigorously" because you hit the gym twice this week for 20 minutes, you're Moderately). - Exercise to improve overall health (mental, sleep, immune system, etc). Don't "double count" exercise calories, just set your PAL level and that's it. - Don't eat less than 1500 / 1300 calories for men / women respectively and try to get some nutrients. Ignore everything else, it is just adding complexity. Weight loss should be "Simple but hard." "Complex but easy" doesn't exist unfortunately, at least not in the medium to long term. Instead, you'll just burn out faster. So K.I.S.S., make it boring, make it a habit, eat whatever you want below your TDEE. PS - Starting new exercise (or periods in women) can cause short term water weight increases in the order of 1-6 lbs. This is caused by inflammation. It is completely normal and will go away on its own. Just be patient.
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- 2011Hacker News 讨论帖120 分 · 61 评
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