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The Trouble with Fructose

“Fructose is a strange sugar.” That’s what I wrote here in July 2006, and I still think that it’s strange.

But I didn’t know the half of it when I wrote my earlier article about fructose. I didn’t know why it was so strange. And in this case the “why” is crucial.

Fructose is strange because it is the sweetest sugar and yet has the lowest glycemic index, so it has little immediate effect on our blood glucose levels.

When we assign a baseline value of 100 to sucrose (table sugar), then fructose has a sweetness factor of 173, according to Dr. Robert Lustig, professor of pediatric endocrinology at the University of California, San Francisco. Glucose, which we digest even faster, rates at just 74. Maltose, the highest glycemic sugar, is just 32, and high-fructose corn syrup, a mixture of fructose and glucose, has a sweetness score of 120.

Yet the glycemic index of fructose is only 19. That’s the average of six studies.

I often wondered how fructose could be so sweet and yet so low glycemic. I also wondered why so many people think that high-fructose corn syrup is bad for us.

Joe Anderson has studied the tight relationship between fructose and advanced glycation end products (AGEs). His disturbing report, “AGEs and Aging – Sweet Suicide,” helped form my thinking about AGEs, which I wrote about here in May 2006, September 2006, and this May. While accepting his concern about AGEs, I nevertheless questioned his concern about fructose, because I didn’t understand it.

Now, after reading two other experts this week, I get the point. The first was science writer Gary Taubes. His new book, Good Calories, Bad Calories, is really shaking up my thinking, even though I haven’t finished reading it yet, much less having taken the time to digest his extensive and profound critique of the received wisdom that we must minimize the amount of fat that we eat.

Taubes’s book is controversial and bound to stimulate debate for years to come. Gretchen Becker, my good friend and fellow writer here, reviewed the book on October 28 and October 30.

Gina Kolata reviewed it in October 7’s New York Times, to which Taubes responded on October 28.

All of these articles are well worth reading. In addition, Taubes has agreed to answer our questions at HealthCentral.com about his new book.

Fructose is just one small part of Taubes’s book. Yet it was an important eye-opener for me.

“Because fructose barely registers in the glycemic index, it appeared to be the ideal sweetener for diabetics,” Taubes writes near the beginning of his discussion of fructose on page 197. “By defining carbohydrate foods as good or bad on the basis of their glycemic index, diabetologists and public-health authorities effectively misdiagnosed the impact of fructose on human health” (page 199).

The trouble with fructose is its impact on the liver, which almost exclusively metabolizes it. That’s the key point.

It’s different from glucose. That sugar goes directly into our bloodstream so that our tissues and organs can use it as energy, with only 30 to 40 percent passing through the liver.

“The more fructose in the diet, the higher the subsequent triglyceride levels in the blood,” Taubes writes on page 200. While our health authorities have focused largely on the health risks of high LDL cholesterol levels, Taubes demonstrates that our triglyceride – fat – levels are even more important in terms of our risks for heart attacks.

And especially troublesome for people with diabetes is that high-fructose diets lead us to secrete more insulin, which in turn leads to more insulin resistance. That’s because fructose seems to block both the metabolism of glucose in the liver as well as the synthesis of glucose into glycogen, the way that the liver stores glucose.

It’s even worse, Taubes writes. Fructose is perhaps 10 times worse than glucose in the way our bodies form AGEs.

It happened that just as I was reading Taubes, my favorite Certified Diabetes Educator brought to my attention a thought-provoking interview with Dr. Lustig. This interview, broadcast originally on Australia’s ABC Ratio National, confirms the outlines of Taubes’s brief against fructose.

“The only organ in your body that can take up fructose is your liver,” Dr. Lustig told interviewer Norman Swan. The first thing that eating fructose does is causing an increase in uric acid, Dr. Lustig said. Fructose inhibits nitric oxide, which would otherwise reduce our blood pressure. “So fructose is famous for causing hypertension (high blood pressure).”

“The second is that fructose initiates what’s known as de novo lipogenesis, excess fat production….And then the last thing that fructose does in the liver is it initiates an enzyme….What happens is that your insulin receptors in your liver stop working….That means your insulin levels all over your body have to rise.”

When I wrote Dr. Lustig today to ask him the name of the enzyme that fructose initiates in the liver, he told me that they call it “c-jun N-terminal kinase-1” or just JNK-1 or Junk-1. “It serine phosphorylates a protein in the liver called IRS-1 (insulin receptor substrate-1), thereby rendering it inactive. This induces hepatic insulin resistance.”
Dr. Lustig also sent me a PDF of a slides for a talk he recently gave that he called “The trouble with fructose.” I swear that this just happens to be the same title I had already decided to use for this article. I have uploaded his article to my site.

Damning stuff, this. In fact, “we’re being poisoned to death,” Dr. Ludwig concludes.

The trigger for the recent trouble with fructose began in 1978, when high-fructose corn syrup entered the market. The most common form, HFCS-55, is 55 percent fructose and 45 percent glucose.

HFCS is now the most common sweetener in the U.S. It has replaced sucrose (table sugar) especially in soft drinks, but it is in many other foods too.

But HFCS is only the tip of the sugar crystal. Sucrose is half fructose and half glucose.

Sucrose goes by a lot of names on the nutrition labels of the products that we buy in supermarkets and natural food stores. Probably no ingredient is more ubiquitous or goes by so many names as sugar. Sucrose includes white sugar, brown sugar, granulated sugar, turbinado sugar, and most of the sugar in regular and blackstrap molasses and almost all of the sugar in maple syrup. One of the trickiest names is “organic dehydrated cane juice.” I’m sure that it fools a lot of people into thinking they aren’t getting sugar. Sucanat is another name for dried sugarcane juice. So-called raw sugar includes demerara, muscovado, and turbinado. More than 100 different sucrose substances exist.

Even the natural sweeteners that I have been using occasionally have lots of fructose. From 90 to 97 percent of the sugar in agave nectar is fructose. Up to half of the sugar in some varieties of honey is fructose.

Even fruit, vegetables, and meat contain some fructose, both directly and as half of the sucrose in these foods. Among meats, corned beef and pastrami seem to have the most fructose, through their added sucrose content. But fruit, vegetables, and meat aren’t much of a fructose problem, because the total amount of fructose we get this way is minimal.

Between 1970 and 2003 our average consumption of fructose increased from less than half a pound per year to 56 pounds per year, according to the interview with Dr. Lustig. “We were never designed to take in so much fructose.”

Now we know why we need to avoid this added fructose in our diet. But let’s not go to extremes. Our bodies were designed to eat the fructose in fruit and vegetables. That naturally-occurring fructose is not the problem. The trouble with fructose is all the fructose and sucrose that we have been adding to our food.

This article is based on an earlier version of my article published by HealthCentral.

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  • Lois at

    Hi David
    I’m using Pura raw organic agave syrup. The label says its low glycemic index is 17. Any comment?

    • David Mendosa at

      Dear Lois,

      I am so glad that you asked. Agave syrup is probably the WORST sweetener that you can use! It does have a low glycemic index, but that is because it is almost essentially pure fructose. And we know now that fructose is damaging to our livers. Please read my articles about this terrible form of sugar.




    Kent is correct in stating that Inulin is a sugar containing fructose.

    According to Wiki:
    About 30–40% of people in Central Europe suffer from fructose malabsorption.[16] Since inulin is a fructan, excess dietary intake may lead to minor side effects, such as increased flatulence and loose stools in those with fructose malabsorption.[17] It is recommended that fructan intake for people with fructose malabsorption be kept to less than 0.5 grams/serving.[17]

    I would avoid using any brands of stevia containing inulin.

    I would also avoid any brands of stevia containing “natural flavors” which doesn’t even tell you what that flavoring ingredient is. “Natural flavors” is just a code word for “we don’t really want to tell you what’s in this”

    The brand NOW makes onene of the most natural stevias.

    Their ingredients are:
    Ingredients: Certified Organic Stevia Extract Powder (Stevia rebaudiana) (Leaf).

  • Larry at

    Meat is not a concern! If it has added sucrose it’s the sucrose that’s the problem!!!!

    Fruits aren’t much of a fructose problem?????

    How so?

    • David Mendosa at

      The fructose is fruit is less of a problem for two reasons. First, we don’t consume that much fructose that way, and second, the fiber in fruit helps us digest it better.

  • CONNIE at

    I’m happy to hear that, thank you so much

  • CONNIE at


  • Kent at

    Great site David. I refer to it a lot. Had Type 2 for about 5 years. Controlled through diet and exercise. I’ve researched a bit and found that inulin is a sugar, not sure why they call it a fiber. It acts as fiber because it cannot be metabolized until it reaches the colon but it is a sugar from the fructose family which is not a good sign obviously due to fructose’s impact on the liver, etc. Inulin is the main ingredient in one of the stevia brands. Main ingredient meaning first listed and potentially 90% of the product with only 10% being raw stevia. Of course other fillers or bulking agents are no more desireable either.

    It is also stated in Wikipedia that the fructose in Agave IS actually INULIN. Something to consider. Continue the great work and writing!

  • Dennis at

    I have started using small amounts of NOW’s Stevia Balance twice a day. It contains inulin and chromium with the stevia, I had purchased the box of individual packets more than a year ago and had used them only occasionally. Recently I had used some in preparing Rhubarb and had an episode of hypoglycemia in the early morning. Since then I have begun using small amounts morning and evening with a lowering of my glucometer readings. I have begun steping down my lantus IU’s in a controlled fashion. I do not know if this the the result of the stevia or some part(s) of the combination, I am scheduled see my diabetologist in a could of weeks. In the past he was not in favor of using some of the ayurvedic preparations that seemed to lower blood glucose because they had not been studied and could not be sure of the mechanisms involved. Comments?

    • David Mendosa at

      Dear Dennis,

      I certainly agree with your doctor that alternative medicines haven’t been carefully studied.

      In particular, I don’t know about chromium. Years ago I wrote a dismissive article about it, and still have my questions. But it comes in many different forms. Again, it hasn’t been carefully studied.

      Still, I would be surprised if it could cause a hypo. Personally, I use Sweetleaf stevia (made by Wisdom Brands). It too has inulin as its bulking agent, and of all possible bulking agents, I don’t know of any that is better.

      Best regards,


  • David Mendosa at

    Dear Diana,

    Thank you. Like you, I have been using stevia for about a year. But the best brand that I found until now was SweetLeaf. It has a bulking agent, a good fiber called inulin. I didn’t know about the NOW stevia, although I use a lot of their other products.

    Best regards,


  • Diana at

    Hello David
    Great website! I have been working my way backwards through all your posts over the last couple of weeks.

    I have been using Stevia for a little over a year now. The brand I use is by NOW Foods. It is pure stevia, organic, no bulking agents, and unless you use too much, it is not bitter at all. It comes with a tiny little spoon. Over 600 servings for $6-$7. (By the way, I do not own any stock or anything in this company, just sharing what I have found to be the best Stevia.)
    Keep up the great information!

  • David Mendosa at

    Dear AJ,

    Erythritol is fine, although some people are concerned that it is made from corn, which is probably genetically modified. But it has a zero GI, as you say and as I wrote at http://www.mendosa.com/netcarbs.htm

    Erythritol also doesn’t cause stomach distress, like the other sugar alcohols do. I wrote about that someplace, but I know that Wikipedia covered this question.

    The problem with erythritol to me is that it is only about 40 percent as sweet as sugar so you have to use more of it. When I used pure erythritol, I also noticed that the label said that it takes a while to “bloom” when you add it to something, and that’s true.

    Truvia, a type of purified stevia, uses erythritol as a bulking agent. Now that I’ve tried many brands of stevia, I think that the Truvia strategy is a good one. That’s because many brands of stevia use maltodextrin as a bulking agent. I don’t like that because it has a rather high GI. Still, they don’t use much of it, certainly not enough to count as any calories in a serving.

    The bottom line for me is that stevia is the very best choice for a sweetener that we have. Just consider what other ingredients the product that you buy has.

    Best regards,


  • AJ at

    Is erythritol bad? Doesn’t it have a GI of zero? Do all stevia products use it? It seems like my sweetener choices had gotten down to agave and stevia. Now agave is out. Is stevia out, too? I’m not even concerned because if diabetes, but my kids’ insulin response to sugar and carbs and its affect on brain function and ADHD. Do you know any info sources about that?

  • David Mendosa at

    Dear Jo,

    The bulking agent in Truvia, which is erythritol, is made from corn nowadays. So you I think that you are right. Thanks for your valuable comment.

    Best regards,


  • Jo Schrubbe at

    Truvia is made from genetically modified corn. Not a good choice! For more information on GM foods go to http://www.responsibletechnology.org

  • David Mendosa at


    Agave is unfortunately almost pure fructose. Some forms of stevia are not bitter. Have you tried Truvia?

    Please see http://www.mendosa.com/blog/?p=283


  • Jason at

    Thanks so much for this article, I just purchased agave thinking it was best for me (insulin resistance, pre-diabetic) – I can’t stand stevia’s bitterness. As for fructose in fruits – what is your recommendations regarding bananas? All the info I’ve read says they are to high GI, but the raw foodies live on them and cure their diabetes.

  • David Mendosa at

    Dear Lisa,

    I think that using stevia as a sweetenered is a great idea. But not agave, which is essentially pure fructose, the worst sugar.


  • Lisa at

    I work in an assisted living home. Several of the residents have diabetes. I was thinking of trying to incorporate Stevia and Agave as sweeteners. Not too much–just in some gelatins and teas–. Do you think that’s a good idea?