Possible Objection to Lustig’s Research

Although Lustig’s hypothesis that the fructose in sugar being the root cause of a host of metabolic problems and America’s obesity epidemic seems quite sound, it is in part due to the strength of his voice in the academic field. Most people do not hear of other objections to his research, including me. However, I recently came across David Despain’s blog Evolving Health that included an interview with Dr. John Sievenpiper of St. Michael’s Hospital, University of Toronto. Sievenpiper is also a qualified expert in the field: he is the lead author of three recent systematic reviews and meta-analyses evaluating fructose’s effects on body weight, blood pressure, and glycemic control in humans from randomized controlled feeding trials.

Access the full interview on this link: http://evolvinghealthscience.blogspot.com/2012/05/fate-of-fructose-interview-with-dr-john.html

One of his main arguments is that the studies Lustig uses to support his claims were made on animals, which cannot be directly translated to the effects of fructose on humans.

I think you hit the nail on the head. There is really the disconnect between animal carbohydrate metabolism and human carbohydrate (or fructose) metabolisms. One of my criticisms of using animal data is that they feed at superphysiological levels at 60 percent energy. No one is consuming that.

The heart of Lustig’s argument has been that fructose consumption causes the generation of dangerous fat in the liver. However,

On top of that, we know that if you look at comparative physiological studies, animals metabolize carbohydrates differently than do humans. In animals on a high-carbohydrate diet not providing excess energy, you find that de novo lipogenesis [conversion by the liver to fatty acids] is anywhere from 50 percent or higher. They basically make fatty acids for at least 50 percent of the carbohydrate [consumed]. De novo lipogenesis accounts for at least 50 percent carbohydrate. In humans, it is very, very hard under isocaloric (neutral energy) conditions, let alone in overfeeding conditions, to push that beyond 10 percent or even 20 percent.

Also, in many of the studies he cites, the animals are given a super-physiological amount of fructose, thus skewing data.

It is easy to get caught up in the one sided view of “fructose as poison”, so the purpose of this post was to temper my own perspective a bit. Sure, fructose is still bad, but I think society could use a little more balanced view. And again, nothing in science is absolute. We certainly do not want this to happen:

That’s the danger — that people will say that fruit is a source of fructose and I won’t consume fruit because it may induce obesity, metabolic syndrome, and so on. It’s not just the lay public that may take this message to heart but professionals. We had an endocrinologist here at our hospital at University of Toronto who was telling patients not to consume fruit because of the fructose content precisely because of all the commentaries, editorials, and reviews that Rob Lustig had been publishing. The danger is that people will take the message to extreme. They’ll start saying “I should cut these things out (apples, pears) to cut my fructose exposure.” That is a really wrong-headed approach. When I talk to Dr. Lustig on the side, I do get a sense that he does think that there’s a dose threshold, but it doesn’t come out in the writing, or the YouTube piece.

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