Is fructose bad for you?


Former Executive Editor, Harvard Health

ARCHIVED CONTENT: As a service to our readers, Harvard Health Publishing provides access to our library of archived content. Please note the date each article was posted or last reviewed. No content on this site, regardless of date, should ever be used as a substitute for direct medical advice from your doctor or other qualified clinician.

One of many controversies mixing up the field of nutrition is whether the use of high-fructose corn syrup in soft drinks and other foods is causing the paired epidemics of obesity and diabetes that are sweeping the United States and the world. I’ve ignored this debate because it never made sense to me—high-fructose corn syrup is virtually identical to the refined sugar it replaces. A presentation I heard yesterday warns that the real villain may be fructose—a form of sugar found in fruits, vegetables, and honey. It may not matter whether it’s in high-fructose corn syrup, refined sugar, or any other sweetener.

Sounding the alarm is Dr. Robert H. Lustig, a professor of pediatrics and an obesity specialist at the University of California, San Francisco. He is a key figure in a recent New York Times article called “Is Sugar Toxic?” Here’s some background and the gist of the presentation Lustig gave as part of a weekly seminar sponsored by Harvard School of Public Health’s Department of Nutrition. (You can watch Lustig’s entire talk or a view a similar version on YouTube.)

When fructose is joined to glucose, it makes sucrose. Sucrose is abundant in sugar cane, sugar beets, corn, and other plants. When extracted and refined, sucrose makes table sugar. In the 1800s and early 1900s, the average American took in about 15 grams of fructose (about half an ounce), mostly from eating fruits and vegetables. Today we average 55 grams per day (73 grams for adolescents). The increase in fructose intake is worrisome, says Lustig, because it suspiciously parallels increases in obesity, diabetes, and a new condition called nonalcoholic fatty liver disease that now affects up to one-third of Americans. (You can read more about nonalcoholic fatty liver disease in a Harvard Health Letter article.)

Virtually every cell in the body can use glucose for energy. In contrast, only liver cells break down fructose. What happens to fructose inside liver cells is complicated. One of the end products is triglyceride, a form of fat. Uric acid and free radicals are also formed.

None of this is good. Triglycerides can build up in liver cells and damage liver function. Triglycerides released into the bloodstream can contribute to the growth of fat-filled plaque inside artery walls. Free radicals (also called reactive oxygen species) can damage cell structures, enzymes, and even genes. Uric acid can turn off production of nitric oxide, a substance that helps protect artery walls from damage. Another effect of high fructose intake is insulin resistance, a precursor to diabetes.

In the 1970s and 1980s, the “fat is bad” mantra prompted a big shift in the American diet. People and food companies replaced fat, often healthy fat, with sugar, almost always refined sugar. But this sort of low-fat diet—one rich in refined sugar and thus in fructose—is really a high-fat diet when you look at what the liver does to fructose, said Dr. Lustig.

Experts still have a long way to go to connect the dots between fructose and nonalcoholic fatty liver disease, obesity, diabetes, heart disease, and cancer. Higher intakes of fructose are associated with these conditions, but clinical trials have yet to show that it causes them. There are plenty of reasons to avoid sugary drinks and foods with added sugar, like empty calories, weight gain, and blood sugar swings. Lustig offers another.

Every year I attend scores of talks on health and nutrition. Few prompt me to change what I do or what I eat. Lustig’s talk has me looking at the amount of sugar I take in, and thinking hard about sugar in my children’s diets.


  1. Mike Doleman

    The Dr. Lustig youtube lecture indicated that fructose from fruits was not as bad because one also gets the fiber from the fruit which effects the biochemical outcome.

    I infer that the message is not only too much fructose but also not enough fiber. Maybe “artificial” fiber is part
    of the dietary solution if you really like your sugar?

    Also, can anyone tell me where to get a readable copy
    of those biochemical pathway charts from the video?

    • Avatar
      P.J. Skerrett

      Mike —

      The message is actually “too much fructose.” As I say in the post, the huge increase in fructose in the American diet comes from eating sugar, or foods sweetened with sugar. It doesn’t matter whether it’s cane sugar, beet sugar, or high-fructose corn syrup. All are about 50% fructose. Fructose delivered via fruit may not be as bad because we tend to get it in smaller amounts.

      Here’s a link to a diagram showing what happens to fructose in the liver, from an article in the Journal of Clinical Investigation:


  2. Luis

    People and the things were surrounded with brainwash us to what healthy or not. obesity is the biggest problem in united states of America. Belly fat is the dramatic aftermath

  3. kayus

    The talk about fat is bad is a way to create an awareness about the high rate of fatty foods most people love to eat.Many diseases are linked to the unhealthy eating habits of many of us.

    So thanks doc, for letting us in on what kind of fat we should eat.

  4. Chris

    What about the 50% glucose in sucrose? Everybody seems to have forgotten that. It contains just as much energy weight for weight as fructose, is easily absorbed and, being the reference for glyceamic index determination, has a GI of 100%. I suppose we may be exceeding the liver’s capacity for fructose metabolism by bombarding it with masses of freely available fructose derived from freely available sucrose. A few centuries ago even a king had no way of obtaining the amount of sugar so readily available to all of us.

    • Avatar
      P.J. Skerrett

      Chris — That’s a key point of the post. Americans get most of their fructose from sucrose (which is 50% fructose) and from from high-fructose corn syrup (which is also about 50% fructose.)

  5. sean

    I have lived with gout for over 5 years now and my dr. has told me to stop eating foods with lots of fructose and to drink more water and even cherry juice.


    I agree that both are bad, but you don’t mention the real difference between eating HFCS in lieu of sugar and why over consumption can lead to diabetes… Fructose is absorbed slower than glucose. It doesn’t cause a rapid rise in blood glucose levels, because, as you said, it is processed in the liver. The pancreas doesn’t react to as if it is a sugar. And by not reacting to the High Fructose Corn Syrup, the pancreas doesn’t produce amylin or leptin – hormones responsible for controlling our ability to feel full. As another commenter said, we overeat when we eat foods made with HFCS. This is where the correlation between obesity and High Fructose Corn Syrup is found. The only way to limit obesity is to limit high fructose corn syrup in our processed food products and to educate consumers.

    • Mark Sutter

      As Dr Lustic explains, sugar (cane or beet) is ALSO high in fructose 50% when broken down in the body. Thus sugar and HFCS have the same issues when consumed in large quantities. 20oz of Coke from Mexico made with sugar is just as bad as the same amount of U.S. Coke made with HFCS. Dr. Lustig’s point is how much MORE fructose we are eating today because it is now so ubiquitous – in everything from bread to salad dressing to sausages – because of the HFCS usage explosion. As to what is a “balanced” diet itself is controversial. Is 33% fat, 33% carbs, 33% protein by weight balanced? 33% each by calories? Sound absurd? Why? Dietician A’s “balanced” diet may not be dietician B’s or mine. Finally, if we do settle on percentages, can anyone truly achieve a “balanced diet” if due their workload and family pressures they must rely on mostly processed/prepared foods? BTW, I lost 60 lbs in less than a year (from 245-250 to 185-190)not by cutting intake, but through a very unbalanced diet of tons of fresh and frozen vegetables coupled with moderate amounts of lean meat and whole grain cereals w/ reduced fat milk. I was not aware of the sugar issue at the time, but my diet was low in simple sugars. All the while I did no exercise. (I do now because of my age (68) and what I have learned about bone/muscle maintenance as we get older). I have kept the weight off for over a year.

    • Keith

      I live in Australia. HFCS is not used in Australia yet we have a similar obesity problem to the US. We do consume a similar diet to you but with regular sugra rather than HFCS.

      So obesity is probably not specific to HFCS.

  7. Lee Hardy

    Great post and Good source of information. I was recently diagnosed with type 2 and I am on a mission to research as much as possible on the subject of this nasty suprise. I have been scouring the internet for good sources of alternative recipes for diabetics and hope to build a large database of free to browse yummy recipes.

    L Hardy

  8. edwardjacobhernandez

    alright, now I am alarmed.. Is sugar bad?

    • Keith

      Pretty much any doctor or dietician will tell you that yes, sugar is bad for you. The only exception being when sugar is consumed as part of its natural package – fresh fruit and vegetables.

      Even those that demonize low-carb diets as dangerous fads will agree that sugar is bad for you. Which is odd, because low-carb really means low-sugar.

  9. Tony Phylactou

    I had my first gout attack about 10 years ago.
    At the beginning I was having attacks every 6 months. Then gradually I was getting them
    every 3 months, then every month and eventually every week.
    It started at my big toe and then it was moving sometimes in my knees,and generally all
    around my joints, in my feet.And the pain was agonising.
    I have tried all the cures you can imagine.I tried ACV, lemons, drinking a lot of water, but
    to no avail.I tried water fasting, juice fasting,baking soda, again without success.
    I almost gave up meat, limiting it to only once a week ,gave up alcohol completely,again
    no success.
    I was living on vegetables, lots and lots of fresh fruit, milk ,cheese beans and so on .My
    eating habits could not be healthier ,or so I thought.But my gout was worsening.
    Then I decided to increase the amount of fruit I was consuming, thinking that if some fruit
    is healthy, more fruit will be more healthy.Some days I was eating fruit only ,others over 10
    portions a day.
    And alas my gout instead of improving it became chronic ,it was there all the time.
    I was desperate I did not know what to do.
    And then one day accidentally I read an article about fructose,which is contained in fruit in
    large quantities.It said that it increases uric acid, in a matter of minutes.
    Fructose is also present in table sugar, and in HFCS, which is used in soft drinks.
    I put two and two together and realised what I was doing wrong.
    I stopped eating fruit and all other sugars, for a period of 3 weeks,and by magic I saw a
    dramatic improvement.Pain was gone, swelling was gone, I was fine.
    I re introduced fruit again in my diet but reducing them to 1 or 2 a day, and my gout completely
    I do eat more meat now, and occasionally have an alcoholic drink, and thank God everything
    seems to be fine.
    Fructose was my enemy.

  10. Rita

    See how they are tricking us to overeat.
    Watch sugar the bitter truth children’s version

  11. Anonymous

    Fructose has a direct co relation to Triglycerides Levels in our body. However this is quite an explanation to clear some myths.

  12. Iain

    Interesting truths are coming out. One thing I would strongly encourage for consideration is that there is no sugar in sodas. Artificial (from corn) chemical sweeteners are used such as glucose and fructose. When I was a kid, I could drink enough soda. I would start to feel full or even sick if I drank too much. My body would say stop. However, fructose is processed by the liver and therefore does not provide the same “signals” that I have had enough or too much. The manufacturers know this. I have learned about sucralose today, or “splenda”. I have realized today that this has been making me sick for years. I have learned the truth, I encourage you to do the same thing. Splenda, surcalose, is making a lot of people sick.

  13. The Pool Pump Guy

    Great article,I just wish the general public would be introduced to this type of information on a regular basis instead of bombarded with commercials urging them to buy the latest sugar rush.


  14. Cynthia Papierniak

    My google alert for HFCS picked up your article. The thrust is correct, but you have mistated some facts. There is no sucrose in corn. If there were, the CRA would have had an easy time making a lovely sweetener. Corn starch is pure glucose. It took a synthetic enzyme, glucose isomerase, and some nifty technology before the CRA could produce HFCS.

    Also, HFCS is not the same as sugar for this reason.
    There is only one sucrose. You can throw a sugar bowl against the wall and it will still be 50%fructose:50% glucose. This is not the same with HFCS. HFCS exists in different grades, denoted by the percentage fructose. The
    CRA claims that the grades used are HFCS-42 (42% fructose), and HFCS-55 which is used by Big Soda. However, last year USC researchers assayed locally obtained bottled soda and found that three national brands had 65% fructose. Seems like the CRA is monkeying with the formula.
    It gets worse. Cornsweet90 a product of ADM is HFCS-90. This intensely sweet HFCS is used for low-cal, low-fat
    products. Why? The same sweeteness can be imparted with fewer calories. Sounds like a caloric bargain until you realize that your’e getting a bolus of extra fructose your
    liver doesn’t need. Finally, crystalline fructose, now used in beverages like “Vitamin Water” is not
    fructose gently extracted from fruits or vegetables; it is crystallized high grade HFCS. After extensive column chromatography the upper limits of HFCS used to be 90% fructose. But I just read a product blurb on a Chinese corn refiner’s website and they boast 95% fructose. Wonderful.. Now consider Dr. Lustig’s preaching about the excess fructose we have been ingesting the last three decades. Sure, sucrose, aka table sugar, is not good for you, but at least you know what you are getting. HFCS is a black box. The fructose:glucose ratio has been maniupulated by the CRA. So when you read the ingredient “HFCS” on the box or bottle, you have no idea what you are getting in terms of fructose. Sadly, your liver does.

  15. Mr152

    Our entire food supply is tainted. We are getting fatter and sicker as a result. Dog poop tastes good with added sugar and what we’re eating is in that category. Sugar is also addictive. It’s a pretty grim situation. Willpower over diet doesn’t work. Regulation of the 5 corporations in control of our food seems to be the only way.

    • Cmac120

      Now hold on, Mr152. Don’t you think you are over-generalizing by saying “Willpower over diet doesn’t work”? Maybe that’s true for you but I’ve lost 25 lbs. in the past 10 weeks just by cutting down portion sizes per sitting. Keep in mind, if we don’t take responsibility for our own diet then no one will. No one is forcing us to get a double quarter pounder, large fries and large Coke every day…that is a decision we make ourselves. It’s all about habits and making the effort. There is ALWAYS a choice. I discourage everyone I know from being a typical American and letting corporations tell us what to do and in this case, what to eat. Be your own person and take control of what you eat. You’re not helpless, make the choice to eat healthy.

      Just FYI, I didn’t mean to make this sound like a personal attack on you, sir. I am just trying to encourage you (and everyone else) to filter out the constant advertising for bad food that you see everywhere and eat what we know is good for us as human beings.

  16. Robyn Flipse, MS, RD

    I have been dealing with good food/bad food questions, such as this, my entire career as a registered dietitian and consultant to food and beverage companies. The questions begin when media draws attention to an association made between the incidence of some health problem and the consumption of a single food or ingredient, just as you describe here. Because people might not fully understand scientific methodology, they are easily frightened by unproven hypotheses, or a highly inflammatory video like Lustig’s. Regardless of the targeted food, my answer is always the same: A healthy diet is composed of a wide variety of foods eaten in the appropriate amounts and frequency to meet one’s nutritional and energy requirements. All foods and beverages, including those sweetened with sugar and high fructose corn syrup, can be part of the diet when eaten in moderation as part of a well-balanced plan complemented by regular physical activity. This is also the best message for your children

    • Bill Kelly


      Have you watched Dr. Lustig’s video? Sugar has invaded EVERYTHING we eat. Ketchup, Mayonnaise, Tomato sauce, virtually every processed food. How about the entenmann’slow fat diet where we replaced a little saturated fats with LOTS of sugar. In this way, Dr. Lustig is saying eat fructose, just eat it in the form our grandparents ate it: fresh fruit. Please watch the video.

    • J. D.

      I’m not an MD and it doesn’t take much to understand that our food supply is rife with HFCS and fructose. These sugars impair our satiety signals which in turn causes us to eat more, raises insulin, stores fat. Why do i think my MD uneducated self knows this? Well because and educated MD told me and when i cut my sugar intake I dropped 20LBs without a thought. I did not starve myself, I ate when I was hungry, difference is I cut out sugar and grain, I feel fuller longer as a result and my 6 pack is looking good. I just don’t understand why folks are not getting it. Sugar is addictive and my guess is your fretting over losing your favorite meal which is probably a grain or a sugar…think about!

    • Diane Stegmaier

      In other words, like all RDs, you have the rote answer but never add, “don’t confuse me with facts.”

    • Samera BSc, MSc, PhD

      I do agree very much with Robyn Flipse. I am not a dietician, however, my PhD research was based on the metabolism of fatty acids, ethanol and sugars. I think some can misunderstand this article in a way suggesting fruit is bad for you (do forgive me as I have not watched the video yet, I will be commenting after I have). I think what needs to be made clear is that, this is not the case. The point is that anything in high amounts can be detrimental to your health. I would be worried about the intake of alcohol and a high intake of fats and sugars than to worry about my 5 a day. I think the main point is pop drinks or anything high sugars is detrimental for your health, but then too much of anything is harmful, is it not?

      I mean look around at the constant torture smokers put their lungs through, alcoholics or even regular alcohol drinkers put their liver through. How about the battering we give our heart with the high consumption of fatty foods. They all effect the organs. The liver is able to metabolise fructose, provided at a slower pace as the breakdown of fructose is complex, but then so is the breakdown of alcohol. The point to all those who have now started to develop a fear of fruits is, 5 a date will not harm you. Remove the fizzy drinks, pop, fatty fast food, eat more fruit and veg and exercise regularly, increase the consumption of fish and reduce the red meats. Understand and grasp the concept of a balanced diet with exercise and I’m sure you will live longer.

  17. Andrew

    Yep. The video “sugar: the bitter truth” on youtube tells it all, and in a way scientific people can understand.

    Fructose is the same as alcohol except it does not affect the brain in ways we can detect, but just like alcohol only the liver can take it. And too much will hose your liver and the rest of your body.

    Finally people are listening!!

Commenting has been closed for this post.