Why is Fructose Bad For You? The Bitter Truth

Dr. Robert H. Lustig is a pediatric endocrinologist, an expert on obesity in children and a very talented speaker. He’s also the guy who brought the dangers of fructose into mainstream attention.

His presentation above, Sugar: The Bitter Truth, is a 90 minute lecture that delves deep into the science and biochemistry behind fructose consumption, with 3 million views.

This video is a must watch… I’ve seen it 3 times already and it is about as entertaining as a movie in my opinion. He published a book on sugar in December. I haven’t read it yet but I’m planning to.

Why is Fructose Bad For You? Some Important Points

Sugar cubes

Sugar (sucrose) and High Fructose Corn Syrup both supply a significant portion of the total calories in a standard western diet.

They both consist of two simple sugars… glucose and fructose.

Glucose also comes from starches like potatoes, our bodies produce it and every cell on the face of the earth has glucose in it. Glucose is a molecule absolutely vital to life.

Fructose however, is not. Humans don’t produce fructose and throughout evolutionary history have never consumed it except seasonally when fruit were ripe.

Glucose and fructose are metabolized very differently by the body.

The key thing to realize, is that while every cell in the body can use glucose, the liver is the only organ that can metabolize fructose in significant amounts.

When people eat a diet that is high in calories and high in fructose, the liver gets overloaded and starts turning the fructose into fat.

Lustig and other scientists believe that excess fructose consumption may be a key driver of many of the most serious diseases of today, including: obesity, type II diabetes, heart disease and even cancer.

The Harmful Effects of Excess Fructose

Eating a lot of fructose in the form of added sugars may:

  • Make your liver synthesize fats, which are exported as VLDL cholesterol, which leads to dyslipidemia (blood tryglicerides and cholesterol), fat around the organs and ultimately, heart disease (1, 2).
  • Increase blood levels of uric acid, leading to gout and elevated blood pressure (3, 4).
  • Cause deposition of fat in the liver, potentially leading to non-alcoholic fatty liver disease (5, 6).
  • Cause insulin resistance, which ultimately leads to obesity and type II diabetes (7, 8).
  • Insulin resistance leads to elevated insulin and insulin like growth factor (IGF-1) in the entire body, which may ultimately cause cancer (9, 10).
  • Fructose doesn’t affect satiety in the same way as glucose, making you eat more total calories automatically if your fructose intake is high (11).
  • Excess fructose consumption may cause leptin resistance, throwing body fat regulation out of whack and contributing to obesity (12, 13).
  • Sugar may be downright addictive (14).

Leptin resistance, elevated insulin and vicious addictive cycles of cravings and binge eating are a recipe for fat gain disaster.

If potentially leading to obesity, cancer, heart disease and diabetes isn’t reason enough to stop eating added sugars, I don’t know what is.

Be aware that not all of this has been proven beyond a shadow of a doubt in controlled trials, but the evidence is still very strong and more studies will paint a clearer picture in the coming years and decades.

Fructose From Added Sugars is Bad For You, Fruit is NOT


It’s important to realize that all of this does NOT apply to fruit.

Fruits aren’t just watery bags of fructose, they are real foods with a low energy density and lots of fiber.

They’re hard to overeat on and you’d have to eat ridiculous amounts to reach harmful levels of fructose. In general, fruit is a minor source of fructose in the diet compared to added sugars.

The harmful effects of fructose apply to a western diet supplying excess calories and added sugars. It does NOT apply to the natural sugars found in fruits and vegetables. Period.


  1. Kris,

    I couldn’t agree more that all excess sugar does is lead to obesity and disease. Best to cut all that stuff out.


  2. Wonderful lecture, I really enjoyed it. Thanks Kris.

  3. What about coconut sugar? There has been a lot of claims recently on choosing coconut sugar over other types of sweeteners for diabetic or pre-diabetic patients. According to studies, coconut sugar has about 35% fructose in it. Is coconut sugar good or bad?

  4. How does one break the sugar addiction? I know it’s bad but I am addicted

    • That’s a tough one, the only thing that has worked for me is complete abstinence. Haven’t touched added sugar or gluten in over 4 months.

      I’m writing an e-book about food addiction, plan on releasing it in February.

      • Looking forward to it.

      • When you say you haven’t touched sugar in 4 months… do you mean ADDED sugar? (not fruit itself) Just want to clarify!

      • Dianne Thomas says:

        Chromium piccolonate stops initial sugar cravings. I’ve used it in the past and then once your body gets used to not having sugar it stops craving it. I have been off sugar 6 months now and enjoy the incredible sweetness of fruits, which I didn’t when I was addicted to sugar.

        • I actually broke away from added sugars by switching to fruit. The fibre makes me feel a lot more full so I don’t quite eat as much sugar as I used to (counting sugar in fruits), plus I’ve generally felt healthier than before. I do eat a tiny square of 99% coca dark chocolate every day because I love it, and also because it’s apparently good for you.

          I treat myself with a sweet every once per week or fortnight. Helps me not to cave in and binge on sweets, and it acts as a tasty reward for work I do.

          I’m a bit skeptical of using Cr-III Picolinate if only because I don’t want to start a new addiction, especially since I know myself to go wild certain times.

    • Emma Lowrey says:

      Just wanted to chime in to say that something that can help with breaking a sugar addiction is to find awesome recipes for “desserts” that are free of added sugars. That way your mind doesn’t feel deprived at least.

    • Egeorge, the way I did it was to go on a juice fast for two weeks. Once you break the sugar craving that way (it was not easy) and make a little effort to not use added sugar or eat sugary processed food it becomes easier with time. Good Luck.

  5. Brilliant video, thanks for posting. The science really made me think a great deal about how careful I have to be when buying any sauces/dips where the sugar lurks. Ive been low carb/no gluten/no sugar and eating fats for a month now and I feel great. Just have to get some recipes for my own sauces to go with my food.

    • Thanks for the comment, you can easily find lots if you google “low carb sauces” and “paleo sauces” – many blogs and even entire cookbooks are dedicated to this way of eating.

  6. Sarah Willard Gray says:

    Kris, thanks for the newsletters. They keep me on track, latest from my new eating habits is a weight loss of 17lbs in 4 weeks and blood pressure down from 148/90 to 120/61 last week. My doctor was amazed and so was I.
    Many thanks,

  7. Matt Timmers says:

    What about organic honey? Should that be cut out as well?

    • Honey is 38% fructose so I think the same would apply to honey as it is a more concentrated form of fructose that you would usually find. I would limit my honey intake for that reason.

  8. I was wondering about comments made about CVD. My understanding is that plaques start from a macrophage responding to inflammation, then adsorbing LDL to make a foam cell. This to some extent is why CRP can be used as an indicator for heart disease. The foam cell then sends out all kinds of crazy signals, generating more inflammation, and then eventually more macrophages engage at the site and adsorb LDL. I hadn’t considered that fructose interacts with JUNC-1. So, is it necessarily that fructose leads to LDL and thus CVD, or could it be that fructose leads to inflammation, which leads to more active macrophages and more LDL to convert them to foam cells?

    • I’m definitely no expert on the pathophysiology of heart disease, but my understanding is that it is a little bit of both.

    • I didnt watch all the video, but from my understanding, high blood glucose damages blood vessels, which initiates atherosclerosis. This damage to the blood vessels then triggers the cascade response of LDL and increase in plaque. So, without excess sugars in the blood, there wouldnt be a cascade in the first place. But once the damage begins, the LDL in blood and immune response make it worse. Hope this helps a bit.

  9. You harp on fructose so much, but how often does anyone consume solely fructose? Fructose is almost always found in a ratio close to 50/50 with glucose. The same ratio exists in fruit, honey, table sugar, and (heaven forbid) high fructose corn syrup. As long as fructose is ingested with equal amounts of glucose there is no real problem.

    All the studies that like to point out how evil fructose is are performed using ONLY fructose. (Which, yeah, when consumed by itself does exhibit different effects than a nice 50/50 blend of glucose/fructose such as decreased satiety.) Its the amount of sugar people consume that leads to all your scare tactic points in your above thoughts. Not the form so much. So quit bagging on poor fructose so bad. The country has had enough skewed information.

  10. On Glucose, it is needed throughout the body, but I think that in the bitter truth, they say it is as bad as fructose, once the body has received it’s fill, and the waste path for it is as bad as for fructose. That part wasn’t completely clear to me in one watching. But it is an important point one way or another, because in the US diet overconsumption of sugar is a problem. The people who get the memo on fructose, one thing they do is search out stuff like pop made with cane sugar, etc… but when the channels are maxed out, that may not be a solution. Not to mention the calorie load.

  11. So, what is the sugar found in fruits? I was always under the impression that it is called Fructose. How can fructose be bad for you, but it is in fruit and you say that fruit sugar is good for you? I am probably over thinking, just want to be sure. Nice article.

    • Fruits have fructose, but also fiber and lots of water. It is very hard to eat too much fructose if you only get it from fruits.

      I wouldn’t worry about fruit, but avoid added sugars.

      • What about fruit *juice* without added sugars? I currently have someone trying to tell me that fructose is only ok if the fruit is eaten whole – once it’s in juice form it’s just as bad as drinking a soft drink, even without added sugars. I find this difficult to believe.

        Why would the orange juice be any different consumed from the orange than if I squeezed it into a glass? Why would the apple juice be any different consumed from the apple than if I put it through a juicer?

  12. Sten Wispuu says:

    I don’t get why would he not mention the consumption of fruit in his speech… fructose is bad, it kills you and so on. Wouldn’t kill him to mention the effect of the fructose in fruits. Would all the fruitarians be still alive if “fructose” was poison?

    • He does mention it in the video, somewhere close to the end if I remember correctly. But perhaps he should have made a bigger deal of it, a lot of people now believe that fruit causes the same problems as foods high in refined sugar, which isn’t true.

      • Patricia says:

        I always gain weight in the summer. I really believe it is because I eat lots of fruits. I don’t eat junk foods, cookies, cake, etc… but I have been eating melons, berries, etc… This happens every summer.

        I realize that I really cannot eat sugar, but it is so difficult.

        Thanks for this article.

  13. Ryan Rodwell says:

    “Humans don’t produce fructose and throughout evolutionary history have never consumed it except seasonally when fruit were ripe.”

    That’s just absolutely not true. We evolved in the non-seasonal tropical forests where fruit was abundant all year round.

  14. Holly Park says:

    Go one step further and think outside the box on fruits and vegetables… how do we know all were for human consumption? Just because the FDA put them on the list does not mean they are good for OUR health. The FDA also said to eat lots of grain, bread, flour etc, and allowed fructose into our food supply, thanks to that we have a record amount of obese people and diseases.


    • Humans evolved eating both animals and plants and studies show that fruits and vegetables correlate strongly with improved health.

      Of course, there are some plants that can have harmful effects, but plenty of others that are perfectly safe to eat.

  15. How come that fructose is bad, when the first step in Krebs cycle is izomerisation of glucose into fructose?

  16. I felt relieved when I got to the end of the article and it clearly said that eating fruit won’t provide a significant amount of fructose. I hardly use sugar and eat sensible amounts of fruit every day. Thank God!

  17. I’m relieved now because I love fruits so much and I’ve been avoiding sugar for eight years now, even though I don’t have diabetes. But I also learnt to be careful of honey, is it true? Then I read that honey aids in weight loss, I’m confused again.

  18. I agree with one of the replies above. The article and the video is presenting completely skewed information. Most people who read “fructose is bad” will throw away fruits and vegetables that are remotely sweet. What is a ridiculous amount of fruit? I know people who live on a fruit based diet, which is a ridiculous amount to me and are still as thin as a pencil.

    So if it is true that it is impossible to consume large amounts of 100% fructose then this video and article does not add any value except scare people into more bad food decisions.

    • The article clearly states “The harmful affects of fructose does NOT apply to the NATURAL sugar in fruits and vegetables. Just to Added sugar in the diet. Period.”

      • The article states that BECAUSE it claims it is impossible to eat so much fruit that you will get unhealthy amounts of fructose, due to the amount of fibre and water also present in fruit.

        Prashant asks a valid question – what is considered a ridiculous amount of fruit? Most health organisations recommend two serves of fruit a day, some people would eat a lot more than that.

  19. I somewhat doubt the author, yes fruits contain nutrition, antioxidants, and can have certain beneficial products, but it is still fructose, it may be politically correct to say fruits are good for you, in reality human beings only ate fruit as a seasonal venture in many parts. Fructose is bad but you have to remember it served a useful function in places where people did agriculture and work, fructose did cause insulin resistance and fat storage for energy, thus making energy work slower and conserving it.

    This may not be relevant for a society that has jobs that often are in cubicles or light labor, but may be relevant to folks who suffered famines back in the day, did back breaking agriculture labor, or those in the jungle and wilderness who hunt and forage for food.

    This fructose could be useful in certain athletes or those who want energy stored and not available right away. Just because fruits are natural doesn’t mean they should be eaten a lot, there are benefits and it’s better to get vitamins and minerals from natural sources such as fruits and vegetables, but potatoes are natural, sugar and honey are natural too and humans have been eating it for thousands of year.

    • In many parts of the world, fruit is seasonal all year round. The type of fruit varies, but you can always get some kind of fruit at any time of year.

  20. If fructose is bad for you (compared to sucrose), there’s no reason honey wouldn’t be also. The only reason fruits do not apply seems to be because fructose is diluted with fibers. Which would be true of anything else you eat when absorbing either HFCS or honey.

  21. I have just read “sweet poison” by David Gillespie. It is very easy to read and he explains in simple language how the various forms of sugar are metabolised and utilised. He researched it because he was overweight and had tried just about every diet invented. White sugar is a very processed sugar.

  22. I’m no expert either, but it seems to me, when you boil all of this information down, the point would be eat “whole foods”. Since that is when fructose is not dangerous… even in juicing I would think that it would be best to juice the whole fruit, even sometimes a bit of the peel.

    Just think about what is being said… fruit is not bad for you, you could never OD on fructose from fruit. That says plain and simple, when fruit is processed, therefore concentrated or changed, it is as dangerous as anything else processed.

    I don’t believe fruit or fructose is bad for you when consumed the way Mother Nature created it. Eat clean, simple and whole foods and there are no problems. Also Glucose would seem to me to be the same. I cannot eat any grain that has been processed without blowing up (inflammation), but I can eat a whole boiled or baked potato in moderation and have no problem.

    I do however get a serious craving for potatoes once I start, it is processed after all when you cook it and does become more concentrated in sugar the longer it sits around.

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