

[Epistemic Status | Okay, listen up. People seem to think that because I am a doctor, I must know something about this field. This is totally false. I got maybe three hours worth of lectures on nutrition in medical school, which were around the sophistication level of "Eat less and exercise more, okay?" So I am as new to all of this as anyone else. I am giving my opinions on some of the things I read, but they are NOT MEDICAL ADVICE and you should NOT TRUST ME and if you do you will GET A HEART ATTACK AND DIE.]



I said I would write a review of Good Calories, Bad Calories, but I don't have the book in front of me so I'm going to have to work from memory. So here goes.



Eating less cholesterol won't actually decrease blood cholesterol or heart attack risk in most people. Lowering blood cholesterol actually leads to higher death rates in the elderly populations at greatest risk of heart attack. The amount of fat you eat has no effect on your risk of heart disease. Dietary fat has no particular ability to make you obese beyond any other form of food.



These are not the revolutionary contrarian claims of Good Calories, Bad Calories. These are the things that most people in the medical establishment paying attention already agree upon. That I had never heard any of them after four years of medical school suggests that a lot of the medical establishment isn't paying attention, and if they're not paying attention what hope for the average person trying to start a diet?



The contrarian claims are more interesting still. Let me start three that, are in retrospect, blindingly obvious.



1) "Primitive" cultures have extremely varied diets, yet practically none of them ever suffer obesity. This includes the Eskimo, who eat obscene amounts of meat and blubber (basically solid fat) and almost nothing else while staying perfectly lean and free from cardiovascular disease. When the start to adopt the ways of "the white man", immediately obesity and cardiovascular disease go through the roof. This suggests that it's not fat or meat or whatever the latest bogeyman is that's causing the problems, but something about processed "civilized" foods. Taubes sticks the blame on refined carbohydrates - white flour and sugar. These are things primitive people would have little access to, but which are staples of food in modern societies.



2) The obesity epidemic started, most people agree, around 1980. The average American now eats less fat than the average American in 1980 - probably because of all the low-fat foods around and "eat less fat" diet advice. That alone pretty much ends any believability of the idea that the obesity epidemic is due to dietary fat.



There are three "macronutrients" - things that food calories can be made of - protein, carbohydrate, and fat. If you eat the same amount of calories, then cutting down fat means you have to raise one of the other two macronutrients. We have mostly made up for our low-fat diets by increasing carbohydrates - hence the infamous decision of the Food Pyramid to place bread at the bottom as the healthiest and most important food. If Taubes is right that refined carbohydrates are the problem, we would expect this decrease in fat and increase in carbohydrates to correspond with the obesity epidemic getting worse, rather than better - as indeed happened.



3) The idea that weight change is based on how much you eat minus how much you exercise, compounded over time, assumes an astounding level of lifestyle stability. I've been at about seventy kilos, give or take, for the past five years. This stability suggests I'm consistently taking in the same amount of calories as I'm burning.



But imagine that tomorrow, before going to bed, I eat a single French fry, and I repeat this each night for the next decade. Now I'm taking in one French fry's worth of calories more than I'm burning. Each day this adds a little more fat to me, until by the end of the decade I weigh a thousand pounds. This jars pretty wildly with our experience. First, it seems unlikely that without any particular effort I've kept my calorie level perfectly stable, to within a margin of error of one French fry, for the past five years. Second, it seems unlikely that a healthy person who eats okay and exercises but also eats one extra French fry a day would end out at a thousand pounds.



[EDIT: Wrong. See http://squid314.livejournal.com/350821.h tml?thread=3854949#t3854949]



Obesity Set Points



The failure of small dietary changes to produce major changes in weight suggests something more complicated is going on.



Nutritionists tend to scoff at the idea that weight is anything beyond a simple calories in - calories out balance, and for understandable reason. The First Law of Thermodynamics, that mass/energy can neither be created nor destroyed, means that food mass/energy has to go somewhere. If you put it in your body, either you burn it for exercise or it stays in your body and becomes fat. This is why smug people sometimes say that they're following "the physics diet" of eating less and exercising more as opposed to thinking diet pills or fad diets can do much good. Fancy biochemistry stuff has nothing to do with it, mere sophistry on the part of people who claim to have "bad metabolisms" in the same way people used to say they were "big boned".



But even my limited amount of medical knowledge is enough to know this isn't true. There are a bunch of diseases - Prader-Willi Syndrome, hypothyroidism, hypothalamic lesions - that cause obesity. There are even drugs you can take that cause obesity - some of the antipsychotics are famous for this. And by playing around with mice genes, you can get anything from disgusting spherical mice to mice that look like they just got out of a concentration camp, even if they're all feeding out of the same bowl of Mouse Chow.



The book's solution - which I think is pretty standard now - is to say that yes, fat has to follow the laws of thermodynamics, but thermodynamics doesn't specify what is controlling the equation. It could be that your diet and exercise are controlling the weight gain. Or it could be that some innate tendency to weight gain is controlling the amount you diet and exercise.



And it seems to be some combination of the two. Realistically, I know not everything is determined by some mysterious inner process - sometimes I just see a cupcake, and want it, and eat it, and I know my having eaten it is determined completely by the fact that I happened to come across it at that moment and no one was watching (obviously a mysterious inner process could have prevented me from eating it by making me feel really full, but that's different). On the other hand, I accept that a lot of the time I eat things it's because my body is telling me I'm hungry, and a lot of the time I don't eat things it's because my body is telling me I'm full, and a lot of the time I exercise it's because my body is telling me I'm antsy, and so on.



So the idea is of an obesity set point. If you get fatter than your body's hidden set point, it makes you a little less hungry and more willing to exercise until you get back down. If you get leaner than your body's hidden set point, it makes you a little hungrier and more tired until you get back up. It is subtle, complicated, and more than enough to sabotage the diet plans of nearly everyone.



Taubes' work supporting the concept of an obesity set point is really spectacular. He talked about both terrible-sounding studies where scientists forced people to subsist on starvation diets, and fun-sounding studies where scientists forced people to eat as many sundaes as they could stuff into their faces. In both cases, people went to desperate lengths to return to their previous weight, and felt absolutely miserable when denied the opportunity (these studies disproportionately came from the military - in every other setting, people just gave the scientists the finger and broke the study rules after a few days). And this happened whether or not the subjects were fat or thin - it wasn't like being fat provided a "buffer" where you were okay with a semi-starvation diet while your fat burned, you were just as desperate to return to your (high) set point as your thin friend was to return to her (lower) one.



This was accompanied by fascinating animal experiments where they would try to trick rats. Suppose a rat usually ate a 10 calorie diet. They would try to trick the rat by giving it a food that looked and tasted exactly like its old food, but was ten times as calorically dense; the rat would eat a tenth as much food and maintain its weight. If they gave it a food that was only a tenth as calorically dense, the rat would eat ten times as much - and maintain its weight. If they surgically stuck food into the rat's stomach, the rat would eat exactly as much additional food as was necessary to maintain its accustomed caloric input and its weight.



So people (and rats) are really good at maintaining their obesity set point. How come some people have higher set points than others, and why does this change over time?



Low Carb Dieting



Taubes' theory is that it has to do with insulin. Best known as the hormone that goes wrong in diabetes, insulin controls a wide range of bodily processes relating to energy balance. He says that refined carbohydrates (especially sugar) produce so much insulin that the body eventually becomes accustomed to it ("insulin resistant"). Then it is unable to respond to insulin's role in keeping the obesity set point, the set point inches up, and you end up with a vicious cycle of getting fatter and fatter. If you stop eating carbohydrates, your insulin gradually returns to normal and you get thinner.



This is a big part of the principle behind the Atkins Diet, and I think Taubes does a good job in demonstrating that the Atkins Diet, and similar low-carbohydrate high-fat diets, do better than traditional diets in weight loss as well as being pretty safe. Mainstream studies are starting to agree with him, even though for years they were hurling invective against it and declaring it was unsafe for reasons which I still have never heard adequately defended.



How Doomed Are We?



I mentioned on Thursday that I do not trust myself to be able to evaluate every controversial issue, and that I believe a brilliant and compelling crackpot will usually be able to convince me of false ideas in domains where I lack expertise. One obvious solution is to default to trusting the establishment. If the establishment is trustworthy, this is okay. If establishments are consistently untrustworthy, this means I am doomed, and for all I know any random crackpot could be correct and I have no way to be sure and I basically fall into total Cartesian doubt about everything.



Taubes brought me pretty close to the edge of that abyss. If all nutrition guideline makers were so wrong for so long, how can I trust the next group of scientists who say they know something? Climatologists who say global warming exists? Biologists who say Darwinian evolution acting alone can create complex organisms? The arguments on both these topics would take more than a lifetime to wade through entirely and there are extremely clever people making extremely sophisticated statistical arguments on both sides.



I am no longer quite at the edge of the abyss for a few reasons.



The first reason is that it seems Taubes is wrong. That is, a lot of his criticisms of the establishment are correct, but his own pet theory of carbohydrates and insulin seems to seriously fail to hold water. In fact, it seems so bad that it's hard to rule out deliberate dishonesty, which makes me skeptical of some of the rest of his points as well.



(or this could just be the "I am too quick to believe rebuttals and in fact to believe the last thing I read" problem I mentioned on Thursday)



Even though that doesn't make the establishment right, for me it goes a long way to redeeming them. Part of Taubes' point was "When I put it together like this it seems so obvious, and yet everyone missed it for decades." But it only seems obvious because he leaves out the important experimental results that contradict his point. The establishment did not miss those results, and so never settled upon his theory as the Solution To Everything.



So I no longer blame the establishment for missing the One True Theory. Flailing about wildly is a perfectly acceptable tactic in a field as complicated as nutrition. I do blame them for presenting the science as settled instead of honestly stating "Yes, we're flailing about wildly here."



Taubes discusses some of their motivations. The main one, and one I can respect, is that politics works different from science. In science, it is virtuous to say "You know, we think we've found a link between fat and disease, but really we're just flailing about here. Come back in fifty years and we'll tell you some more." In politics, you have to be able to tell people "Eat less fat!" or else they won't do it and maybe they'll die of disease. Since we were just coming out of the fiasco with smoking, when people waited years and years to say for sure that smoking caused lung cancer and goodness knows how many people died of preventable lung cancer in the interim, it is at least easy to see why erring in the opposite direction would be tempting.



Reassuringly, there seem to be some trustworthy smart people in the establishment. The critique I linked to above is by Dr. Stephan Guyenet, who seems like the smartest and most reasonable nutrition blogger I've found so far (Steve Rayhawk's brother, who is an amateur expert in the area, has recommended a different guy I need to listen to at some point, but he seems to broadly agree). He has published research in the field and no one seems to be burning him as a witch.



He paints a picture of the current state of the research which looks like an establishment which has accepted the same facts Taubes points out (even if they haven't quite permeated to the public yet) and is now doing research in what looks like a promising direction - leptin resistance. This new paradigm explains some of the carbohydrate results as well as some of the conventional results. When I did med school, one of the smartest surgeons I studied under was also doing work in leptin resistance and said it was eventually going to explain obesity, it was just fiendishly complicated to work out.



So it looks like the system was never as bad as Taubes thought it was, didn't miss an obvious idea the way Taubes accused it of doing, and eventually righted itself and started limping in the right direction.



It just probably killed a few million people with diets that didn't work in the process. And actively mocked and condemned the ones that did. Oops.



[EDIT: Or here's a claim that older research shows low-carb diets just really don't work that well. But see here for some more recent research showing they might.]



I find it interesting that although the contrarians' biochemical claims were mostly wrong, their solution - low-carb diet - seems to be sort of in the right direction. It would not surprise me if this were a pattern. Skilled amateurs are unlikely to beat the experts at disentangling complicated scientific problems, but they might be better at noticing the way empirical evidence is going. In fact, given that they're less bogged down in theory, that might even be a strong point for them.



Last thoughts



I would highly recommend Good Calories, Bad Calories.



Its negative claims - the ones demolishing those of the standard nutritionists - seem broadly correct, and form a really good survey of the current state of nutrition science.



Its positive claims - the carbohydrate/insulin theory of obesity - seem probably wrong, as far as I can tell. But everyone who responded to my post a few days ago with "Oh, I would never be fooled by convincing-sounding contrarian claims" - well, your challenge is to read GCBC without having read the criticism above and tell me whether you avoided being fooled by it.



It also just provides a really good snapshot of a scientific field and how exactly consensus opinions form. That's something most science books don't go into, and it's sort of scary.



As for diet? I'm trying to cut carbs. I will never be any good at it, because bread is my favorite food and my previous diet relied on it almost exclusively, but I'm trying to be at least a little better. I just discovered low-carb tortillas, which I would have thought unlikely, but they're very good and have only a few calories from carbs each. I'm paying less attention to fat and cholesterol, and more to carbs and (especially) raw number of calories.



But I have to admit I'm not convinced it will do much good. Nutrition science is slightly beyond the voodoo stage, but not by much, and it seems likely there's enough genetic variability that any universal prescription will be useless.