Fructose found to be more harmful than glucose

Table sugar, the form of sugar individuals generally spoon into their tea or coffee or use when making, say, cakes and puddings, is comprised of sucrose. Sucrose is technically termed a ‘disaccharide’, a term used to describe sugars which are comprised of two individual sugar molecules joined together. Those two sugars, in the case of sucrose, are glucose and fructose, and when sucrose it is digested down to its constituent sugars prior to absorption into the bloodstream.

The glucose in sucrose undoubtedly contributes to the glycaemic load of the diet, and the more sugar someone eats, the greater the rise in blood sugar levels. More glucose in the bloodstream means more insulin, of course, which as we know can contribute to health issues such as insulin resistance, Type 2 diabetes, heart disease and, of course, weight gain.

In contrast to glucose, fructose has traditionally enjoyed a healthy reputation, mainly on the basis that it does not raise blood sugar levels. Fructose is also the predominant sugar in many fruits – something which tends to bestow it with an image of healthiness.

In recent years, though, a steadily growing mound of research demonstrates that fructose, while it does not raise blood sugar levels directly, can nevertheless have some profoundly toxic effects on the body. Interest here has been sparked, at least in part, by the fact that increasing amounts of the sweetening agent ‘high fructose corn syrup’ (HFCS) are making their way into the diet. HFCS is made cheaply by the chemical treatment of the starch in corn, and contains fructose and glucose in roughly equal measure.

HFCS began being used in food production in meaningful quantities in the 1970s, but these days contributes substantially to our diets as an ingredient in foods such as breakfast cereals, cereal bars, baked goods such as biscuits and cakes, pre-prepared desserts, sweetened yoghurts and soft drinks, as well as some more savoury foods including cooking sauces, condiments (e.g. ketchup) and crackers.

The potential for fructose to harm health was further demonstrated by a study published recently on-line in the American Journal of Clinical Nutrition [1]. In this study, healthy, normal-weight men aged 20-50 consumed in beverage form either:

  1. 40 g of fructose a day (medium fructose)
  2. 80 g of fructose a day (high fructose)
  3. 40 g of glucose a day (medium glucose)
  4. 80 g of glucose a day (high glucose)
  5. 80 g of sucrose a day (high sucrose)

Some of the men consumed none of these drinks and were counselled on how to reduce the amount of fructose in their diets. The study lasted three weeks. A wide range of body measurements and biochemical parameters were checked as part of the study.

Here are some of this study’s most notable findings:

  • C-reactive protein, a marker of inflammation, increased in all 5 groups
  • LDL cholesterol size decreased in the high fructose and high sucrose groups (smaller LDL particles are associated with heightened risk of cardiovascular disease)
  • General changes in LDL particle size consistent with raised cardiovascular disease risk occurred in the medium fructose, high fructose and high sucrose groups
  • Waist-to-hip ratio increased the medium fructose, high fructose and high sucrose groups (higher waist-to-hip ratios are associated with an increased risk of conditions such as heart disease and Type 2 diabetes)
  • Fasting glucose levels increased in all five groups
  • Leptin levels increased in the medium glucose and high glucose groups (leptin is a generally desirable hormone to have around, in that it speeds the metabolism and helps curb appetite)

Put this all together and one would have to conclude that fructose, as supplied in sweetened beverage from, is worse for us than the same amount of glucose. The best thing, of course, is to have neither.

References:

1. Aeberli I, et al. Low to moderate sugar-sweetened beverage consumption impairs glucose and lipid metabolism and promotes inflammation in healthy young men: a randomized controlled trial Am J Clin Nutr 2011 First published online June 15, 2011

37 Responses to Fructose found to be more harmful than glucose

  1. A.B. Dada 22 June 2011 at 11:11 pm #

    I have correlative evidence in my own diet lifestyle about this. I rarely eat fructose or glucose, but a serving of potatoes doesn’t put me to sleep or cause me long term (3 days?) hunger like having a few apples or oranges. Forget about HFCS, I won’t touch it ever again.

    Thanks, Doc!

  2. TerryJ 23 June 2011 at 3:33 pm #

    4. 80 g of glucose a day (high fructose) ?

    Typo ? Should be (high glucose)

  3. John Briffa 23 June 2011 at 3:40 pm #

    Thanks Terry

    Corrected now.

  4. timothy price 23 June 2011 at 6:48 pm #

    “Waist-to-hip ratio increased the medium fructose, high fructose and high sucrose groups”

    I think that the brain-to-mouth ratio becomes huge in articles like this. As a vegetarian, quite thin, and eating mostly fruit, I find these articles misleading at best. Use your scales as a tool to manage your weight and eat fresh, raw foods for the most part. Easy.

  5. Doctorm 24 June 2011 at 12:10 am #

    This is just saying that refined foods, in this case sugars, are harmful – not a very profound observation. This is not in any sense a condemnation of fresh fruits which are very healthy and can and should be eaten in large quantities. Incidentally most common fruits are not high in fructose – apples and pears being the main exception

  6. aidanpp 24 June 2011 at 12:59 am #

    ‘Leptin levels increased in the medium glucose and high glucose groups’. Would you be able to account for this increase? Surprising that sugar consumption could have a desirable affect on the body like this…

  7. John Briffa 24 June 2011 at 6:44 am #

    aidanpp

    Don’t know. But I suspect it’s part of the body’s self-regulatory processes. Leptin tends to be secreted in greater quantities, say, when we put on weight, and helps to lower weight again by stimulating the metabolism and suppressing appetite. Might have something to do with this.

    Doctorm

    This is not in any sense a condemnation of fresh fruits which are very healthy and can and should be eaten in large quantities.

    I agree that a sugar-sweetened soft drink and a piece of fruit are not the same thing, but don’t think that fruit should be given a free pass. It is, other than water, main sugar, after all (though some are better than others in this respect). Would you recommend that someone with, say, insulin resistance or diabetes eat fruit in large quantities? (I wouldn’t).

  8. Eric 24 June 2011 at 10:44 am #

    I repect the research. But I feel that pointing out the negatives in HFCS is like shooting fish in a barrel. Once you’ve eliminated HFCS products and refined sweeteners, what’s next? I would like to see more discussion on fruit, and natural sweeteners like agave nectar, and why they should be avoided. Eating fruit lessens my cravings for bread, which I thought was a good thing.

  9. Phil W 24 June 2011 at 11:47 am #

    Surely every individual has different dietary needs and metabolises food differently and therefore demonising any natural food is wrong. If a person has no problem metabolising carbohydrates then there can be no issue with including them in the diet. That includes fruit, grains etc. Look at what happened when flawed research over fat was taken as indisputable.

  10. J Beach 24 June 2011 at 1:50 pm #

    When I was first diagnosed with diabetes in the 1950s, all fruit had to weighed and was included in the permitted 120 grammes per day of carbohydrate. (though a whole apple was more satisfying than half a slice of bread)

  11. tal 24 June 2011 at 3:01 pm #

    Agave nectar can be as high as 92% fructose. Unless/until some does a specific study on agave, my own assumption is that it’s worse than HFC. Moreover, the manufacturing process is similar for both HFC & agave ‘nectar’,,,neither of these is gently squeezed from their respective plants…

  12. John Briffa 24 June 2011 at 4:02 pm #

    Eric

    What might be better would be to have no cravings for bread. If this is due to blood sugar imbalance, then eating a lot of fruit may not be helping much.

    Phil W

    I agree that different people have different propensities to handle carbohydrate. I did qualify my comments re fruit in comment 8. A grain rich diet is, in my experience, bad news for almost everyone. And there’s a lots of evidence to support this observation. By the way, there never was any good evidence to incriminate naturally-occurring fat (and the still isn’t). Don’t think this is true for grains though.

  13. tal 24 June 2011 at 4:50 pm #

    “High doses of free fructose have been proven to literally punch holes in the intestinal lining allowing nasty byproducts of toxic gut bacteria and partially digested food proteins to enter your blood stream and trigger the inflammation that we know is at the root of obesity, diabetes, cancer, heart disease, dementia and accelerated aging. Naturally occurring fructose in fruit is part of a complex of nutrients and fiber that doesn’t exhibit the same biological effects as the free high fructose doses found in “corn sugar”.”

    http://drhyman.com/5-reasons-high-fructose-corn-syrup-will-kill-you-5050/?utm_source=Publicaster&utm_medium=email&utm_campaign=drhyman%20newsletter%20issue%20#20&utm_term=Get%20the%20story

  14. Chris 24 June 2011 at 5:02 pm #

    If its’ content is reliable this (Link) lends some discussion to sugars and triglycerides, and tabulates fructose content of various fruits.

    I think an issue arises from the similar etymological origins of ‘fructose’ and ‘fruit’. Justified concern cast in the direction of ‘fructose’ can transpose as an unjustified level of suspicion in the way of ‘fruit’. Is there a measure of automacity to think fruit is consistently high in fructose?

    If our ancestors in evolution once survived in a predominantly arboreal habitat did fruits make up a distinguished component of the diet and were they exposed to fructose? I should think fruit did and the ancestors were. But were the fruits like those we eat today? I doubt it. Actually, I’m in no way clear what fruits were available in a forest habitat several million years ago, but a couple of things strike me as being important: First both ripe and unripe fruits were likely consumed, and ‘fruits’ don’t have to be sweet types anyway. I don’t suggest we can say with certainty that avocados were on the menu back then, but while not being sweet, avocados are undeniably a fruit. It is difficult to know precisely what foods were on the menu in a long extinct habitat let alone estimate how abundant was fructose itself. Second our perceptions of ‘fruit’ and its attributes are influenced by our very selective relationship with modern cultivars of all plants including fruits. Botanically tomato is undeniably a fruit but officialdom in the USA has ‘ruled’ tomato is a vegetable.

    We ought to have some evolutionary legacy of being adapted to diets that include fruits, and one might wonder, some degree of adaptation or tolerance to fructose. Fruits are commonly cited as being rich in newly identified phyto-nutrients and anti-oxidants with beneficial consequences for health.

    I wonder, is fructose bad per se, or does fructose become an issue when inclusion of fructose in the diet exceeds a certain threshold, and/or if issues arise from more fructose being included but with correspondingly less inclusion of something else? If fruit does not deserve a ‘free pass’, as you posit, John, does fruit deserve a ‘restricted’ or ‘limited’ pass, and how could we more clearly define the limits of the pass?

    I agree in general with the thread and one theme in general; the willingness to permit ‘process’ to be an increasing feature of the diet is not healthy. Oranges or other fruits may be worthy of a ‘restricted pass’ into the ‘five-a-day club’, but do juiced fruits deserve equal status, promotion and privileges trading off supposed merits of whole-fruits? Juices are profitable for some and convenient for others; each considerations that can prevail above others.

  15. david manovitch 24 June 2011 at 6:09 pm #

    Human beings or any animal should never eat pure sugars of any description in anything other than very small in frequent amounts.

    Fructose is surely only deleterious if consumed pure or almost so in the corn syrups mentioned above. Fruit based diets do not seem associated with the diseases of western ‘civilisation’, but are relatively high in fructose. I am uncomfortable with this high/low dichotomy that characterises many of Dr. B’s reports and the responses from correspondents. This kind of extreme polarisation tends to produce harm in my view. No food constituent should be be treated as requiring consumption to a high degree, such as ‘high carb’ or ‘high fat/protein’. There needs to be balance, the precise nature of which is difficult to determine unfortunately. What seems to be becoming clearer is that foods from the plant kingdom offer the best health, though I would personally consider that seafood should be added to that. The so-called Paleo diet does seem sensible to me.
    Clearly there are individual food substances best avoided in high quantities as excess can be toxic. The example of Antarctic explorers eating dog livers caused severe vitamin toxicity for example. Excessive consumption of carrot juice has caused severe illness and death I believe.

    One thing abundantly clear is that the mainstream western diet is very unhealthy for many of us.

  16. DoctorM 24 June 2011 at 7:13 pm #

    Type 2 – replace all sugary desserts, cakes, biscuits etc by fresh fruit 3 good pieces a day
    Type 1 – according to affect on blood sugar
    I totally agree about not demonising any natural food. Eat as wide a vsriety as possible of fresh vegetables, fresh fruits, raw nuts and seeds, natural meats, fish and eggs, many herbs and spices, legumes and varied wholegrains. The problem with modern diets is obsession with a narrow range of foods – huge amounts of wheat (in various forms)as sole grain, grossly disproportionate amounts of dairy foods and huge amounts of refined and processed foos (sugar, oils, processed meats etc)

  17. J Lawrence 24 June 2011 at 7:22 pm #

    Doctorm and Dr. Briffa:

    Has any research compared the effects of HFCS and similar amounts of fructose in fruits, and in freshly squeezed juice? I’ve read that the processed juices have been shown to be detrimental, and that cloudy juices fare better, but I haven’t read anything about how cloudy (including freshly pressed, non-filtered) juices and fresh fruits compare to foods using HFCS – or to having nothing.

    It would also be useful to know how these compare to other snacks and drinks – particularly those you can give children. So, for example, will your children be healthier and more fit if they never get freshly pressed apple juice, and only have water instead? Should I be grubbing up my apple trees?

    Or is the problem with HFCS actually not the fructose itself, but the form in which it’s being delivered to the body?

  18. John Briffa 24 June 2011 at 7:30 pm #

    DoctorM

    Type 2 – replace all sugary desserts, cakes, biscuits etc by fresh fruit 3 good pieces a day
    Type 1 – according to affect on blood sugar
    I totally agree about not demonising any natural food.

    No-one’s ‘demonising’ natural foods here. But just so I’m clear, why are you recommending that diabetics (who by definition, don’t handle sugar well) eat a food that is, generally, rammed full of sugar? What are they getting here that they can’t get with less sugar elsewhere? What are they missing out on if they don’t have it?

  19. ed 24 June 2011 at 8:20 pm #

    Well everyone knows this I think but I don’t see why you mention fruit (Fructose is also the predominant sugar in many fruits – something which tends to bestow it with an image of healthiness.)You don’t want to compare fruit with stuff that has HFCS in it …….

  20. J Beach 25 June 2011 at 12:06 am #

    I’d like to think that not all craving for bread is about blood sugar imbalance. Maybe the smell of really good fresh bread is what does it. A loaf of newly baked granary has me beating it off with a stick.

  21. Xenia 25 June 2011 at 9:08 am #

    The answer here is: ask yourselves what is truly natural.

    Agave syrup is not natural since you do not see it growing (or flowing) in the Nature. It is a very highly concentrated sugar and the fact that it was made from a plant does not make it “natural”. (The only exception may be stevia because it even increases insulin sensitivity but even stevia should not be consumed in big quantities.)

    But even if a substance IS natural, like honey, it does not mean that we should constantly eat a lot of it. Our primal ancestors have maybe found honey once in two years, they did not eat it every day. And remember, unlike us they lived in times when food with high glucose content was scarce and therefore welcome.

    Fruit? DoctorM, what on Earth makes you think that fruit is so precious – there is nothing you can get in fruit that is not available in vegetables. And no, fruit is not natural, far from it. Nature did not intend for fruit to be so big and so full of concentrated sugar – this is all men’s doing. In the past centuries we have cross-bred fruit beyond recognition – and for what happens when men try to breed something without understanding how it really works, taking into account just one or two traits that they seek to enhance (like size, color, etc.) please take a look at what we did to dogs. All the so called ‘pure breeds’ are the most degenerated ones. Because humans were only trying to achieve a certain height, form of skull, tail length, color mix etc. So each pure breed has a lot of typical ailments and diseases, from allergies to metabolic or respiratory ones … All because we did not know what the hell we were doing. Today’s gene modification is the same – the tools are a bit more advanced but we still do not know what we are doing and while we may be able to change one targeted gene, by using gene guns we change several others with unknown consequences.

    So fruit should be eaten more like a condiment, if at all. Stick to berries, apples (the old, small kinds) and occasional grapes. And there are certainly no fruit juices in Nature. When I was trying to cure my diabetes years ago, my first instinct was to go vegetarian and to go raw. I eliminated all the bread, pasta and grains in general but still my blood sugar shot up. Then I started drinking freshly squeezed juices only – and my blood sugar DOUBLED. That is when I understood what my body was telling me: that this is not the way to go. After I have given up ALL the fruit and also all starchy vegetables, my diabetologist reluctantly told me (reluctantly because he knew I refused to take any drugs) my diabetes was cured. So diabetics and people with metabolic syndrome should avoid fruit until cured and should – above all – only choose organically grown ones.

  22. DoctorM 25 June 2011 at 11:27 pm #

    Fresh fruit contains essential minerals, vitamins, fibre, various sugars in various ratios and perhaps above all loads of beneficial phytochemicals (Flavonoids, ayhohocyanins etc) – also some protein ! The important phytochemicals are not avaiable from any other sources. I suggest 3 good portions a day of many different fruits and 5 good portions a day of many different vegetables other than potatoes. (some potatoes ok but not as part of the 5) Many many studies have shown that high consumption of vegetables and fruits is cancer protective and some even argue that fruits are more protective than vegetables. I recommend you search for and read books by Joel Fuhrman, Paul Clayton, Richard Beliveau, David Servan-Schreiber , Patrick Quillin amongst others. Whole fresh fruit (not juice or dried) is fine and (highly) beneficial as long as one does not have Type 1 diabetes. I agree that many modern fruits have been bred for sweetness so one should not obsess with the higher sugar content ones which is why one needs to eat a wide variety of fruits focussing more at the berries end than at the banana/mango end. However I did find an article suggesting that carbohydrate content even of ancient fruits was quite high though I cannot locate the reference at the moment.

  23. John Briffa 26 June 2011 at 12:51 pm #

    DoctorM

    Fresh fruit contains essential minerals, vitamins, fibre, various sugars in various ratios and perhaps above all loads of beneficial phytochemicals (Flavonoids, ayhohocyanins etc) – also some protein !

    You can get a wide range of nutrients eating non-starchy veg, without the big carbohydrate load.

    Many many studies have shown that high consumption of vegetables and fruits is cancer protective and some even argue that fruits are more protective than vegetables.

    Can you provide these ‘many many studies’ please, or are we supposed to take your word for it?

    Whole fresh fruit (not juice or dried) is fine and (highly) beneficial as long as one does not have Type 1 diabetes.

    Why is fruit no good for type 1 diabetics, but fine for type 2? Can you explain?

  24. DoctorM 26 June 2011 at 2:58 pm #

    References and logic are in the books by the mentioned authors – I urge you to follow up – I am summarising my own interpretation of the opinions of these authors. Fruits contain unique phytochemicals which cannot be found anywhere else. Fresh fruits are not ‘loaded’ with sugar. For example an apple or pear, a bowl of stawberries (or other berries) and a couple of tangerines or a small bunch of grapes would be fine for a day – if non diabetic a lot more could and should be eaten for their unique protective effects. The complete diet counts – I listed what it should contain – a wide range of natural foods – no refined or processed foods. Type 2 diabetes can be reversed by diet. Dr Joel Fuhrman and Dr Neal Barnard claim to have done so and I see no reason to disbelieve them particularly in the light of the Newcastle work reported in the Guardian on Friday.

  25. John Briffa 26 June 2011 at 3:41 pm #

    DoctorM

    You’ve made assertions, I’ve asked for the science, and you suggest that it’s me who has to go looking for it. If many studies are there that support your stance, just quote them (if you can…)

    Less rhetoric and a bit more actual research would be nice.

    Here’s one way of reversing type 2 diabetes – cut the carbs! (including fruit, to be frank). The diets that Drs Barnard and Fuhrman are probably better than what most people eat. Are they optimal for human health? Not in my opinion.

  26. DoctorM 26 June 2011 at 7:51 pm #

    The books I recommended you to read have very extensive references. A quick search found the following review article :

    http://www.drfuhrman.com/library/high_nutrient_diet_n_weight_loss.pdf

    Not perfect because it limits animal products too much, includes dairy (which you will know that some people are allergic to) and does not mention herbs and spices, fungi and seaweed which all have beneficial micronutrients. Unfortunately one of the authors other books is, I think, flawed (Colin Campbell’s ‘China Study’) for reasons I gave in an Amazon review. But I think the “high nutrient, avoid refined and processed” principle propounded in this review article is sound.

  27. CJ Fearnley 22 July 2011 at 1:48 am #

    I have been researching fructose and sugar for the past few months. I have not found anyone who thinks glucose is toxic. Glucose is the energy currency of the body. Fructose is definitely more dangerous: it has some negative physiological effects (it increases blood fat for one). The question is whether fructose (and things like sugar which are 50% fructose) are toxic. I wrote out a summary of my research: http://blog.cjfearnley.com/2011/07/21/sugar-is-a-chronic-toxin/

  28. Sharon 23 December 2011 at 12:29 am #

    What about people (like me) who have difficulty digesting fructose ? Check out Sue Shepherd’s research in Australia or Mercola in California. I blame how I suffer with IBS on fructose!

  29. Larry 7 February 2012 at 1:30 am #

    Doctorm said: “This is just saying that refined foods, in this case sugars, are harmful – not a very profound observation. This is not in any sense a condemnation of fresh fruits which are very healthy and can and should be eaten in large quantities. Incidentally most common fruits are not high in fructose – apples and pears being the main exception”

    What the study shows is that not all refined or unrefined carbohydrates are the same. Fructose is metabolized through the liver. It creates of traffic jam of glucose in the liver when it tries to store it as glucogen. This causes the pancreas to secrete more insulin leading eventually to insulin resistance of the muscles. Glucose alone does not do this.

    The reason why you think fruit derived sugar is “good for you” is based on research of the first half of the twentieth centry that only studied the effects of simple and complex carbs and their effect on glucose in the blood. It’s the overproduction of the insulin that is the problem and Fructose is the main reason.

  30. Lee W 16 December 2013 at 12:14 am #

    Hi, love your articles and regular emails. Thanks!
    Quick question…
    I have a friend who is a type 1 diabetic and he carries and eats lollies, by the handful when his sugar levels drop.
    My question is, if he is doing this chronically over the course of years, wouldn’t it mean that the fructose in the lollies is going to render him susceptible to insulin sensitivity in the longer term and therefore require more insulin to do the same job?
    Do you have any research on the long term effects of fructose (half his lollies) in the type 1 diabetic?

    Thanks heaps in advance!

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