... or read his recent, "controversial" editorial on fructose in Nature, and a related New York Times piece on sugar by Gary Taubes, which relies heavily on Lustig's views. For a detailed review in which Lustig lays out his concerns about fructose's health and metabolic effects, see (1).
Lustig often volunteers, or is asked for, his views on fructose from fruit, as vs. that from added sweeteners, and until yesterday every time I've heard him present his view, it's been that we shouldn't worry about it. He's generally offered two reasons for this seeming inconsistency: first, that the sheer quantity of fructose (including the half of fructose) in fruit is very small and the package large, making consumption of fructose from fruit somewhat self-limiting. The other, of which I'm skeptical, is that even on a gram-for-gram basis, fructose in fruit isn't going to have the same metabolic wallop on the liver as that in a soda or candy bar, because the fiber will slow its absorption. The reason for my skepticism is that when you look at the GI of nearly all fruits -- which indicates how quickly glucose itself, and also glucose released from the liver following fructose conversion to glycogen and subsequent release as glucose -- you see that they can be predicted almost exactly by simply tallying up the (GI x (mg individual sugar)) of all carbohydrates in the fruit, and then dividing by the total mg of all sugars; the fiber just doesn't seem to impair sugar absorption worth a spit.
Yesterday, in a wide-ranging and occasionally surprising interview on a local NPR affiliate, Dr. Lustig admitted (with self-confessed hesitancy over the unintended consequences of the admission) to some nagging doubts about his carte blanche on fruit, and says he is now testing the effects of fructose from fruit as part of total fructose intake (relevant section begins at 35:34 on the mp3):
So, I'm not real excited about saying that in public; you're sort of asking directly. I think that fruit is so much better a choice than virtually anything else in the store -- particularly any processed food -- that I don't want to come down on it. But I would say, fruit is one of those things where I would say, everything in moderation.
Host: Well, and if [our caller] is saying, "Can I have an apple and a banana and a pear in a day, would you say ...?
I think that's fine. Lots of fiber. [...]
The fact is that [in human history], we as humans only had fruit once a year. And that was called harvest time. And then, what happened after harvest time was four months of winter. So in fact, the sugar that we consumed during that month after harvest time, actually increased our adiposity in a way that was adaptive and beneficial, given that we were about to face four months of famine. The problem is that now -- with sugar being available 24/7, 365, and that the total sugar consumption has just gone up everywhere, and very specifically for the food industry's purposes -- that we have basically undone our evolutionary biochemistry in a very negative way. What we have now is maladaptive.
He made that last point, in almost the same words, on NPR's Science Friday:
And then what would come after that? Four months of winter, no food at all. And so putting on those extra pounds in advance of a four-month famine was actually adaptive and actually let us make it through winter so that we could repeat the cycle all over again. It was actually metabolically and evolutionary adaptive.
The problem is that we now have a maladaptive situation because sugar is available 24/7, 365 in amounts that has never been known to man previously. How do we know this is true? Because the orangutans in Papua New Guinea have what are known as masting fruit orgies every January when harvest time comes, and the food falls to the ground, and they do exactly the same thing.
This does seem to be an exaggeration: per one source, while orangutans do indeed get nearly 100% of their Calories from fruit in January, orangutans still get 21% of their food energy from fruit in May.
It's clear, IAC, that you can get significant amounts of the stuff from fruit, even on a healthy diet with no added sweeteners. NHANES data on fructose consumption by Americans shows that, aside from a disconcertingly-high intake in teenaged and early-adult males, and a conservative habit in people ≥51 y, the average American consumes ~50 g of added fructose/d, and 8 g of naturally-occurring fructose (of which, surprisingly, average Americans get more fructose from grains than from fruit and fruit juices). But at 10.5 g per apple, eg, a person could match the total fructose consumption from added sugars of an average American with 5 apples a day. And there's 16 grams of fructose in a cup of pomegranate juice, and 18.6 g/C in grape juice -- surprisingly, much more than the 6 g/C of orange juice.
1: Lim JS, Mietus-Snyder M, Valente A, Schwarz JM, Lustig RH. The role of fructose in the pathogenesis of NAFLD and the metabolic syndrome. Nat Rev Gastroenterol Hepatol. 2010 May;7(5):251-64. Epub 2010 Apr 6. Review. PubMed PMID: 20368739.
This post has been edited by Michael R: 02 March 2012 - 02:30 PM