Der Lustige Lustig

[kirisutogomen]

A couple of years ago a pediatrician named Robert Lustig suddenly became famous due to the popularity of a 90 minute video of a lecture he gave.

I find myself rather disappointed at the credulity with which many people who really ought to know better respond to this sort of thing. Maybe I'll discuss that later.

I've been meaning for at least a year now to sit down and explain the problems with some of the wacky claims he makes. I have now concluded that I'm probably never going to get around to really doing that. A colleague pointed me at a reasonably good critique, and although it is somewhat narrower than what I had intended, it seemed like an adequate substitute for actually going off on a tirade. To try to round it out I poked around and found another critique that somewhat complements the first one.

The Bitter Truth About Fructose Alarmism is a sober, thoughtful criticism of Lustig's claims. Alan Aragon mostly focuses on Lustig's misuse of the clinical evidence. The striking thing to me is the incredibly elementary nature of Lustig's errors. These are the sorts of things that I would have thought would get your tenure revoked.

Wait A Minute, Lustig. is also a fair, nuanced analysis that focuses more on Lustig's very poor knowledge of biochemistry. It is somewhat disturbing to hear that a tenured professor at a well-regarded medical school fails at organic chemistry.

So what's the larger lesson? Well, for starters, if someone is making grandiose claims, like that something everyone in the world ingests is actually a poison, that should be a signal to approach with greater skepticism. Even without that, we ought to be able to pick up on this stuff ourselves. None of the falsehoods mentioned in either of the linked blog entries are terribly sophisticated errors. This is basic stuff, people.

Comments

[psychohist.livejournal.com]

I read the Feinman response so far. While many of his criticisms of Lustig are valid, he makes some errors of his own. To start with the simple one, while the first ingredient in pop tarts is flour, his later claim that it's the main ingredient is questionable, because the second, third, fourth, and sixth ingredients are all sugar.

Lustig is correct that ethanol and fructose share much of their metabolic pathways in the liver. He does omit that these pathways can store glycogen instead of fat, but as Feinman points out, neither fat nor glycogen is inherently good or bad. Feinman seems to making an incorrect assumption here that chemical differences necessarily preclude the sharing of metabolic pathways.

The reason fructose isn't as bad for us as alcohol is because we have evolved a special mechanism, the hepatic portal, to shunt fructose directly to the liver and avoid exposing the rest of the body to it. Lustig ignores this, but Feinman ignores that it's necessary for our well being.

Overall, I think Feinman is making mistakes that reflect the fact that he's a biochemist rather than a biologist; they aren't the same thing. Lustig's errors can probably be attributed to the fact that he's a doctor, not a scientist, and those two aren't the same thing either.

[kirisutogomen.livejournal.com]

Yeah, the Pop Tart things is dumb, but it's hardly central to the issue. What I believe he was trying to suggest (and I could be wrong, since I'm not a telepath) is that while it is misleading to say that "a calorie is a calorie", it is to a first-order approximation true that "a carbohydrate is a carbohydrate" because the metabolic effects of glucose, fructose, sucrose, maltose, maltodextrins, or starch are a lot more similar than they are different.

Feinman is not anywhere claiming that fructose and ethanol do not share a metabolic pathway. He is saying that the mere existence of a pathway tells us nothing about how much that pathway is used. Just because it is possible for me to throw money in the trash with used paper towels does not mean that I treat money the same way I treat used paper towels.

The reason fructose isn't as bad for us as alcohol is because we have evolved a special mechanism, the hepatic portal, to shunt fructose directly to the liver and avoid exposing the rest of the body to it. Lustig ignores this, but Feinman ignores that it's necessary for our well being.

Every metabolic pathway is a "special mechanism" that we evolved. And I don't know what you mean when you say that "Feinman ignores that it's necessary for our well being". Are you saying that Feinman is not explicitly pointing out that without the hepatic portal we would have a lot of trouble safely metabolizing fructose? Well, sure, if we exclude any metabolic pathway, we're not going to metabolize stuff as well. That's not news, it's a tautology. I'm not going to criticize him for not explicitly reminding us that metabolism is good for metabolism.

Finally, "he's a doctor, not a scientist" is hardly sufficient excuse for saying that ethanol is a carbohydrate. If my general practitioner ever said something that dumb I'd find a new doctor pronto, and she's not holding herself out as an expert on metabolism. I'm not expecting that every pediatrician be able to recite the entire Krebs cycle from memory, but I do expect that a doctor took introductory organic chemistry and knows what a carbohydrate is.

[psychohist.livejournal.com]

As I said, I agree with the criticisms of Lustig for the most part. I just think Feinman's response is a case of the blind talking about the blind. The Pop Tarts thing is just illustrative of how Feinman is sloppy about the details throughout his article.

The hepatic portal is not a metabolic pathway. Even if it were, most metabolic pathways are not designed to protect us from what they are metabolizing. Fructose actually is considerably more dangerous to our tissues than glucose or fatty acids, by orders of magnitude, which is why the hepatic portal shunts it directly to the liver without allowing it to circulate through the body even once.

Reply to criticisms.

[richard feinman (from livejournal.com)]

"while the first ingredient in pop tarts is flour, his later claim that it's the main ingredient is questionable, because the second, third, fourth, and sixth ingredients are all sugar."

The label tells you that I was correct. The ingredients you list add up to 17 g of sugar while there are 38 total grams of carbohydrate.

"Lustig is correct that ethanol and fructose share much of their metabolic pathways in the liver."

He is not correct. They have almost nothing in common. They are both capable of being converted to acetyl-CoA and processed in the TCA cycle but that is true of everything that is subject to oxidative metabolism. The processes by which they get there are completely different. In addition, while ethanol can be processed through alcohol dehydrogenase, at high levels, it is processed through the P450 system. This might sensibly be called detoxification. In other words, ethanol at high concentrations is toxic. No such system exists for fructose.

"the hepatic portal, to shunt fructose directly to the liver and avoid exposing the rest of the body to it"

Whereas the liver is the major site for fructose metabolism, other cells, particularly kidney have fructose metabolism.

I and my colleague have recently published a "perspective on fructose," which is available without subscription at http://www.nutritionandmetabolism.com/content/pdf/1743-7075-10-45.pdf.

Finally, it is not for me to say what my level of expertise is but SUNY Downstate dissolved the biochemistry for some reason (I can't help thinking it had something to do with money) and I am now in a Department of Cell Biology, so I must be a biologist.