Monday, June 2, 2014

Can someone please explain to me what Bob Lustig is talking about?

I am with Dr. Lustig in thinking that 'too many Americans eat too much sugar'. Sure, I could believe that. But this explanation makes no sense to me:
When bananas ripen, they brown. The sugar in the bananas binds to proteins in the bananas nonenzymatically, even in dead tissue. That's called the cellular aging or Maillard reaction. That happens to everyone all the time, so we brown inside. You don't want to brown very fast, but we're all browning because that's how we age. But sugar makes us brown seven times faster; it basically kills our organs quicker.
What is he talking about? Someone, please explain.  

12 comments:

  1. It happens, especially with certain eye diseases and in some diabetic complications. Not sure I've heard this invoked as a reason to control sugar intake though.

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  2. I *think* he means that when you increase sugar consumption as much as we have, you also increase the concentration of sugar in your body, which inevitably increases the rate of (Maillard) reaction in your body. He may be trying to make a very straightforward kinetic argument here. That's my assumption of what he's saying. Browning, in his writing, equals Maillard reaction. Though, I don't think the reaction gets as far in your body as producing melanoidins as he seems to be suggesting. Its just an easy descriptor to use.

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  3. NMH the biochemistJune 2, 2014 at 12:19 PM

    From: http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3289531/figure/fig3/

    "Molecular renditions of (A) glucose and (B) fructose, in the linear, chair, and space-occupying projections. In the linear form, both glucose and fructose possess a reactive aldehyde or one ketone moiety, which can bind nonenzymatically to freely available amino groups of proteins. At normal body temperature and pH, the chair form of glucose predominates. This conformation is a glucopyranose (6-membered ring), with equatorial hydroxyl groups and is molecularly stable, which limits its protein reactivity. However, the chair form of fructose is a fructofuranose (5-membered ring) with 2 axial hydroxymethyl groups that exert allosteric and ionic forces on the unstable furanose ring, which favors the linear form. Thus, at normal body temperature and pH, the majority of fructose exists in the linear form and is more reactive with proteins than is glucose"

    AND

    "Fructose is a well-known driver of excessive ROS formation. Molecularly, glucose is found in 2 steroisomeric forms (Fig 3): the majority in the glucopyranose (6-membered ring) form and the minority in the linear aldehyde form, which is highly reactive with ε-amino groups of lysine, generating a ROS with each reaction, known as the Maillard or “browning” reaction. Fructose is also found in 2 stereoisomeric forms: the majority in the linear ketone form (also highly reactive) and the minority in the fructofuranose (5-membered ring) form. The latter has 2 axial (abutting) hydroxymethyl groups, which exert allosteric and ionic forces to the unstable furanose ring and drive it toward the linear form. This difference explains why nonenzymatic fructosylation is 7 times more rapid than protein glycation and why fructose generates 100 times more ROS than glucose."

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    Replies
    1. I don't know if I buy what Lustig is arguing, but at least we hear what he's arguing in 'scientific English', as opposed to his obvious simplification for Vox. Thanks for this, NHM.

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    2. Im reading his book. Its interesting. He has a perspective built from the pediatric patients he sees in his practice:

      www.amazon.com/Fat-Chance-Beating-Against-Processed/dp/0142180432/

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  4. Unfortunately that is flat-out not true. In water at room temperature (not too much of a temperature dependence) glucose is 0.01% linear (http://pubs.acs.org/doi/abs/10.1021/jo010541m, about half is aldehyde and half is hydrate) and fructose is 0.5% linear (http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3254704/).

    Don't get your chemistry from a pediatrics journal :)

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  5. Ahh, the old "we are all bananas on the inside" argument.

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  6. pre-diabetics and diabetics with poor glucose level control have elevated levels of non-enzymatically glycated hemoglobin, and this is used as a biomarker (that averages blood glucose history over last few months). Non-enzymatically glycated proteins and their fragments (advanced glycation end-products) have altered function and degradation (usually they tend to stick around much longer) so having high levels of them is bad for you

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  7. He may be referring partially to AGEs (advanced glycosylation endpoints). My best guess is that this is a combination of poor communication on Lustig's part and the "journalist" who wrote the piece.

    I have personal experience in trying to convey what we would consider a standard piece of scientific work to a supposed scientific journalist, only to have it sound like they took every sentence I said, put it in a blender, and tape random fragments together. I have seen this over and over again with colleagues and friends, who have consistently been misquoted or quoted out of context due to poor editorial work or poor writing. I have never since communicated with the press other than in a formal press release.

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    1. Although I can have sympathy for journalists and editors who do try to tone down the science to make more understandable for public consumption at times it appears the attempts frequently guts the substance or even totally misrepresents the message meaning even any scientist reading it can not comprehend what a story is about. But at the same time it also can be the scientists themselves who can not adequately simplify what they do because used to dealing with like minded colleagues so not practiced in need to water down. Don't know what the circumstance here may be as suggested indeed could be both those at play.

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  8. No idea. 'Lustig' is Swedish for 'funny', though.

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