How Bad is Fructose? David Despain Interviews Dr. John Sievenpiper

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In my article "Is Sugar Fattening?", I discussed a recent review paper on fructose, by Dr. John Sievenpiper and colleagues (1).  It was the most recent of several review papers to conclude that fructose is probably not inherently fattening in humans, but that it can be fattening if it's consumed to excess, due to the added calories.  Dr. Sievenpiper and colleagues have also written other papers addressing the metabolic effects of fructose, which appear to be fairly minor unless it's consumed to excess (2, 3, 4, 5).  The senior author on these studies is Dr. David Jenkins at McMaster University.  David Despain, a science and health writer who publishes a nice blog called Evolving Health, recently interviewed Dr. Sievenpiper about his work.

It's an interesting interview and very timely, due to the recent attention paid to fructose in the popular media. This has mostly been driven by a couple of high-profile individuals-- an issue they discuss in the interview.  The interview, recent papers, and sessions at scientific conferences are part of an effort by researchers to push back against some of the less well founded claims that have received widespread attention lately.

Let me be clear that I feel strongly that concentrated added sugar is not healthy-- and this isn't exactly a controversial position.  Sugar is one of the foods that consistently shows up right before metabolic/cardiovascular/dental health declines dramatically in industrializing cultures.  But no one eats plain granulated sugar, because it doesn't taste very good on its own.  We add it to other foods, reducing nutritional value and increasing energy density, seductiveness, and palatability.  However, none of those problems apply to whole fresh fruit, which is also rich in fructose and has been eaten in quantity by our ancestors for tens of millions of years.  So is fructose really the main problem, or is it the overconsumption of low-nutrition refined foods in general*?

Here's Dr. Sievenpiper:

We didn't set out an a priori hypothesis that fructose doesn't do these things. In fact, our hypothesis would've been "Well, everyone's talking about it. The animal data is suggestive of an adverse effect of fructose." If anything, our hypothesis was that there’s going to be an adverse effect...

We decided to use the gold standard or highest level of evidence in nutrition or, really, in most fields -- which is controlled trials; and, in nutrition, is controlled dietary feeding trials. We wanted to apply the best tools we have, which was systematic review and meta-analyses tools to synthesize that knowledge and information to try to answer the question about really.

Is it true? What we found was that it wasn't. We looked at bodyweight -- which is the Annals [of Internal Medicine] data that you’re aware of -- in each case there was no effect of fructose when it was isocalorically exchanged. There was no adverse effect on bodyweight, blood pressure, or uric acid. We do see a very consistent and strong effect on bodyweight when fructose is providing excess energy.

There are a number of interesting points in the interview.  One of the most informative for me was when he discussed de novo lipogenesis, or the synthesis of fat from carbohydrate.  This process is one of the arguments some people use to suggest carbohydrate is fattening-- fructose is the most efficient substrate for DNL.  Putting aside the most obvious problem with this argument for the time being**, it also turns out that even in the case of fructose, only a small percentage of it becomes fat.

Head on over to David's blog for the full interview.


* I'm asking this question somewhat rhetorically, but just to be clear my current position is that refined fructose and sugar can be problematic in excess, due to their metabolic effect to increase visceral fat, reduce insulin sensitivity, cause lipid abnormalities, and increase blood pressure.  This shows up mostly in studies in which calorie intake increases, but it's important to recognize that subjects in these studies weren't always deliberately overfeeding.  They were sometimes inadvertently overfeeding because they weren't naturally compensating for the calories added to the diet via a large amount of fructose or glucose sweetened beverage.  Although calorie compensation is poor regardless of whether a beverage is sweetened with fructose or glucose, the fructose beverage has more serious adverse metabolic effects.  The practical implication is that if a person adds three sodas to her daily diet, she will end up consuming more total calories and be effectively overfeeding, even if she makes no deliberate effort to eat more calories, and therefore she may in fact suffer some of the adverse effects of excess fructose that only emerge in a hypercaloric context (fat gain, insulin resistance, hypertension, etc.).  Eating whole, fresh fruit should not have the same effect because it doesn't lead to overconsumption in the context of a normal mixed diet.

** If fructose is fattening due to its ability to become fat, then dietary fat should be even more fattening because it doesn't have to undergo an inefficient conversion process-- it's already fat.