Is sugar ‘toxic’?

Professor Robert Lustig argues that sugar, or fructose in particular, is ‘toxic’ and increases the risk for obesity and the metabolic syndrome. He paints a simple picture – glucose is good, fructose is bad – based on the differing metabolism of these sugars. He claims that fructose is similar to alcohol and should be taxed accordingly. Professor Lustig certainly has our attention but do his claims stack up?

In last week’s blog I looked at the reviews on sugar and health conducted by the European Food Safety Authority and the US Institute of Medicine. They both found that sugar is fairly benign with respect to chronic disease but can lower the nutrient density of the diet when intake is high, though this depends on which sugar-rich foods and drinks are consumed.

Professor Robert Lustig from the University of California has a very different view.

Lustig’s case against sugar

The Lustig argument starts off with some well known facts. Over the last 25 years Americans have been advised by health authorities to eat less fat and the percentage of calories coming from fat has indeed declined. However, rather than replacing fats with carbohydrates as was intended, Americans just consumed more carbohydrates and total calorie intake increased. Rates of obesity and the metabolic syndrome have skyrocketed over this period. Sugar intake, especially from soft drinks, is high in the United States.

But Professor Lustig doesn’t see overconsumption of calories as the core problem, or even overconsumption of carbohydrate. He argues that the problem is increased sugar intake or, more precisely, increased intake of fructose. Fructose makes up half of table sugar and slightly more of the high fructose corn syrup used to sweeten soft drinks in the United States. According to Professor Lustig fructose is not just fattening, it’s toxic to humans (he uses the word toxic a lot). High fructose intake is driving the increased rates of obesity and the metabolic syndrome.

Image: source

The claim that fructose is toxic is based on its pathway of metabolism, which differs from that of glucose, the body’s primary carbohydrate fuel. When glucose (or starch) is consumed, blood glucose levels rise and this sugar may be used directly by the brain or taken up and stored as glycogen in the muscles and liver. If there is any glucose left over, it may be turned into fat by the liver and then passed into the bloodstream as triglycerides.

In contrast, fructose is taken up directly by the liver at the earliest opportunity and turned into fat. Put simply, fructose turns to fat. In black-and-white fashion Professor Lustig declares “There is good carbohydrate and bad carbohydrate. Glucose is good; fructose is bad” (he ignores the glycaemic index). Professor Lustig then highlights the commonalities in the metabolism of fructose and ethanol (alcohol), and their common adverse effects on blood lipids, blood pressure and insulin resistance. Then there is a leap of faith – fructose and alcohol are the same. Alcohol is a toxin, so fructose is a toxin. “Fructose is ethanol without the buzz”. Alcohol is taxed for the welfare of society so fructose should be taxed, a theme that Professor Lustig and colleagues took up in their recent article in Nature.

Is fructose fattening?

If fructose is more fattening than other carbohydrates it should be relatively easy to demonstrate this in human intervention trials. Two types of trials have been conducted. In some studies, calories were kept constant, fructose replaced glucose or starch, and weight change was measured. The second approach was to over-feed subjects with different carbohydrates and then see if those who ate the fructose put on more weight than those who ate glucose or starch.

Forty-one such trials were recently the subject of a systematic review and meta-analysis by a team of Canadian researchers. The authors’ conclusions were: Fructose does not seem to cause weight gain when it is substituted for other carbohydrates in diets providing similar calories. Free fructose at high doses that provided excess calories modestly increased body weight, an effect that may be due to the extra calories rather than the fructose.

No smoking gun there. Calories drive body weight.

Image: source

Fructose and toxicity

What about the claim that fructose is toxic to humans? In 2009, Kimber Stanhope and colleagues from the University of California, Davis assessed the effects of high intakes of fructose and found adverse effects on blood lipids, insulin sensitivity and central obesity. This suggests that eating fructose may exacerbate the metabolic syndrome. But, let’s take a close look at the study. Firstly, the subjects were obese. They were also overfed during the study – body weights increased. And fructose intakes were extremely high i.e. 25% of calories. One would have to eat half one’s daily calories as table sugar in order to consume that much fructose. So yes, there were adverse consequences but the subjects were vulnerable and the intake of fructose was unrealistically high.

In a more recent review, Dr Stanhope states that the strongest evidence of an adverse effect of fructose relates to its effect on blood lipids and on this basis argues that the suggested upper limit for sugar intake in the United States of 25% of energy may need to be re-evaluated. Dr Stanhope’s arguments are measured, guided by evidence and tempered by uncertainties, a contrast to the more alarmist approach of Professor Lustig.

Luc Tappy and colleagues provide another balanced review of the possible role of fructose in ill-health and come to the following conclusions about its role in the metabolic syndrome: There is however only limited evidence that fructose per se, when consumed in moderate amounts, has deleterious effects. Several effects of a high-fructose diet in humans can be observed with high-fat or high-glucose diets as well, suggesting that an excess caloric intake may be the main factor involved in the development of the metabolic syndrome.

So, gross over-consumption, of anything, should be avoided. Again, the underlying problem is excessive calorie intake rather than the composition of the diet.

What motivates Robert Lustig?

Robert Lustig is an enigma. He is a credible scientist, a Professor of Clinical Pediatrics, an expert in neuroendocrinology and has published over 90 scientific papers. He rightly criticises the health authorities who advocated the low fat diet on the promise that it would cure society’s dietary ills, but has embarked on a similar single-nutrient crusade, this time targeting fructose. He uses sensationalist language and suggests that there are simple solutions to complex health problems. Surely the lesson of the low fat diet debacle was not to focus on one nutrient or dietary component, especially in relation to the prevention of weight gain where the emphasis needs to be on limiting calorie intake.

Maybe Professor Lustig is a clever public health activist who decided that conventional dietary messages don’t work and that shock tactics were required to motivate his soft drink-loving countrymen to do something about obesity. Hopefully, he is not an opportunist who having created a huge public profile is about to reap a handsome profit.

What do you think?

31 thoughts on “Is sugar ‘toxic’?

  1. What do I think? I just wonder what these guys are giving their kids for snacks! A colleague reminded me of a program in NSW where a fruit and veg program was introduced in the AMS’s, and the rates of otitis media and skin infections dropped dramatically. Yes, it was a small number of kids and yes, (from what I can tell) it wasn’t completely controlled, but I don’t think Lustig could go to these people and honestly say ‘you need to stop providing fruit – it’s toxic’. I’m all for challenging the status quo, but this is not right. What about Indigenous fruit that Aboriginal people have been eating for centuries? Are they toxic? Are we going to tell them to stop eating bush tucker? These people live in a middle-class bubble and it needs to be popped.

    • You’ve missed the point. Dr Lustig deals with this specifically. He even says “Fruit is good, fruit juice is bad”. The issue is around the quantity of fructose and the rate at which the liver has to deal with it.

      Go check out his lecture on YouTube – search for “sugar the bitter truth”.

      • He calls fructose “toxic”. That’s just hysterical nonsense. Fructose is a perfectly normal nutrient. If one over-consumes any normal nutrient, it can have serious health effects. Just about anything can be described as “toxic” if given in large enough quantities.
        In the end, Lustig is totally unconvincing, because the science doesn’t actually back his claims.

        • Lustig is saying that it is fine to eat a reasonable amount of sugar each day, but the does makes the poison. So you agree with him, or you never really understood what he was saying.

          • Hello Aaron. Dr Lustig also said that fructose was bad and glucose was good. When I look at the data it seems to me that glycaemic load is the issue of concern and therefore refined starches should be a focus of our attention. Moderation of intake of nutrient-poor, refined carbohydrates is to be recommended but this was lost when sugar was declared ‘toxic’. Simple nutrition messages may work well in the media but they always fall short in practice. Regards, Bill

  2. Jenna, your comments highlight one of my concerns about using sugar as a measure of carbohydrate quality. Any useful measure needs to be applicable universally. So if fructose is bad for you, then it is bad in a soft drink and bad in fruit. But I don’t think there are many nutritionists who discourage people from eating fruit. Nutritionists need to be a voice of reason as we pass through this ‘sugar kills’ phase.
    That said, some nutritionists seem quite happy to stick with out-dated sugar-based messages – witness the draft Australian Dietary Guidelines. There have to be better ways of assessing the nutritional quality of carbohydrate-rich foods than focusing on sugar and that’s what I’ll be considering over the next couple of weeks. Regards, Bill

    • Specious logic.

      Vitamin A is essential. Too much vitamin A will poison or kill you.

      Lustig doesn’t say fructose is toxic – he says too much fructose, hitting your liver too quickly, without other nutrients (eg fibre) to offset it, is toxic.

      Check out his video on YouTube. Bit long, first half a bit of a boring rant, but the biochemistry from there on in is fascinating.

  3. Your comments on Dr. Lustig’s motivations remind me of another recent crusader for a questionable cause: Dr. Huber, prof emeritus at Purdue. One has to wonder why scientists with respectable careers suddenly start promoting ideas that are at best unproven and at worst simply false. I wrote about Dr. Huber here.

    • Hi Anastasia. In relation to Dr Lustig, I guess the question is: what comes next? Will it be cutting edge research about fructose? Or a book deal? I hope it’s the former. Regards, Bill

      • Hi Bill,

        Sounds like you don’t know- Lustig has a book coming out in December. Even more frustrating is that he uses it as an excuse not to do interviews:

        “As Lustig told Science-ish, when asked for an interview, “I have been issued a ‘gag’ order from my publisher to not do any more interviews until my book is released at the end of December.” The title: Fat Chance: beating the odds against sugar, processed food, obesity, and disease.”

        • Thanks Colby. I didn’t know but all the tell-tale signs were there. Next comes the relentless public relations campaign. The sugar-related paranoia has only just begun. Regards, Bill

  4. In a 2007 ABC interview with Norman Swan (transcript at, I didn’t get the impression that Lustig was exclusively pushing a single nutrient as the cause of the obesity epidemic.
    He covered a number of topics from neurohormonal issues to exercise, as well as glycaemic index and glycaemic load (probably one of the most accessible explanations I’ve read), before going on to fructose which he presumably sees as a major issue.
    I’d be surprised if anyone who works in the area of obesity believes that the problem can be solved by excluding a single nutrient.

      • Re GI & GL.. Umm, he does.

        Key point on fructose was not that it’s evil per se. Rather, it’s the quantity & the rate at which it’s hitting the liver which makes it so bad (in other words, the GI & GL).

        In context of the American processed food diet, people are getting huge amounts of fructose, without other nutrients & fibre to offset it, and this is what’s causing the problem.

        Another example he gives elsewhere is the experiment where one kid juices & drinks 5 oranges (getting all the fructose) and then wants breakfast; whilst the other has to eat the five, can’t make his way through all of them, and no longer wants to eat.

  5. Lustig is most certainly an alarmist. He seems to have kicked off a fashion for saying that we need to ‘demonise’ sugar, which is just bizarre and unhelpful. I’m actually broadly sympathetic to the view that an excess of carbohydrate may be responsible for our obesity problems (though even those are usually overstated). But sugar is a crucial part of many wonderful foods. Even if those foods did prove to incline us towards weight gain, I’d still rather have the pleasure of consuming them.

    There is no food or food group that should be dismissed, even if there may well be a decent amount of evidence we’ve been over-doing the carbohydrate. Lustig’s lecture reveals the same ‘they’-are-out-to-get-us paranoia of many prohibition-inclined activists – hence the very conscious parallels with anti-smoking and anti-alcohol campaigners and the same kinds of policy responses. In Lustig’s case, he believes that Big Food is out to kill its customers. That’s a strange business model.

    Lustig also seems to get some things plain wrong. He says in the lecture that Coke is so sweet to disguise the huge amounts of salt in it. He calls it pizza in a can or something like that. In fact, unless the UK Coke recipe is different to the US one, the salt content is pretty low.

    Wouldn’t mind your thoughts on Gary Taubes, though. He seems less hysterical and better informed. But I know he also sparks controversy, so curious to know what others think.

    • Hello Rob. The ‘they-are-out-to-get-us paranoia’ is the sort of approach that always stirs up the crowd at a conference. The usual conclusion is that the environment is toxic (that word again) and needs to be changed, which usually involves targeting an emblem of ‘Big Food’ for attack.
      I think the obesogenic environment is misunderstood. Rather than it being the presence of a fast food restaurant on the corner, the environmental ‘problem’ is much more fundamental – food is abundant, tasty and cheap. That’s it. Walk into any supermarket or food hall and look around you. And it’s not going to change any time soon, unless there is a global depression or a world war.
      Somehow people need to manage their weight in this superabundant environment but paranoia and simple single-nutrient scare campaigns aren’t going to get us very far.
      Gary Taubes and Robert Lustig provide an interesting contrast. Both try to be controversial and there is nothing wrong with that. I thought Taubes’ article ‘What if it’s all been a big fat lie?’ was a very useful contribution as he highlighted the gap that had opened up between perceptions about the health implications of dietary fat and research findings. Healthy scepticism is useful (hence the existence of this blog) but I’m not sure we are getting that from Robert Lustig. Regards, Bill

      • Bill, I’d like to see you do a piece on the “obesogenic environment”. From my reading, the science on this theory is not very tight. As I understand it started an explanation for the modern ills affecting the Pima Indians, and has evolved from there; the evidence for it is epidemiological and the measurements are gross (ie large-scale estimates of energy-in v energy out) but it lacks measurements on the individuals affected (or unaffected) by obesity. The latter seems to me to be a serious flaw in an otherwise intuitively attractive theory.
        The theory and your statements above seem to suggest we would have to be on the edge of starvation (depression or war), and our innate lipostatic mechanisms would have to be inoperative to reverse current trends – I would have thought it’s more complex.
        This review article describes known multifactorial contributors to the risk of obesity, and some emerging ones:

        • Thanks Rick. I’ll put it on my list. I need to get carbohydrate quality our of my system first. Regards, Bill.

      • While food is abundant, tasty and cheap people still have to be able to eat to excess in order to become obese. A normal appetite system does it’s best to prevent that from happening, but if something blocked that system, say fructose blocking leptin, then there’s nothing to stop people from over indulging when they shouldn’t.

        I’m not saying sugar should be taxed or regulated, that didn’t work for cigarettes or alcohol so it’s not likely to work here, however if people knew exactly how fructose affects their body then maybe they would be more careful with their consumption of fructose.

        Lustig does take an extreme line but sometimes if you want to get a message across you have to be able to stand out from the typical noise in the 24 hours a day news cycle. If taking an extreme line means people are better educated about their diet then maybe that’s not such a bad thing.

        • Hello Dale. I understand your the-end-justifies-the-means approach but rather than overstating the health effects of fructose we could present a more scientifically accurate position i.e. we need to cut some carbohydrate calories out of the diet; focus on cutting down on high GI carbohydrates (including rice and potato) and nutrient-poor carbohydrate foods (such as soft drinks, confectionery, biscuits, cakes, pastries and rice again). Sugar intake would be less but so would the intake of refined starches. Calorie intake would be lower but nutrient intake would be little affected, and metabolic improvements would be expected (blood lipids, insulin and glucose).
          Diet is complicated and so is the body’s response to it. We need to consider all the issues simultaneously, not one at a time. Simple dietary messages appear to be the easiest to comprehend but they are also the most readily misinterpreted. Regards, Bill.

  6. When I read a review like this one: Fructose, insulin resistance, and metabolic dyslipidemia ( I do get concerned about the amount of fructose that I see people eating. Considering the potential side effects of a non-nutritive sweetener that potentially makes food hyperpalatable which can lead to overconsumption in some people. The science is far from certain so why Lustig is so alarmist is a mystery. Maybe it is becoming increasingly difficult to get the attention of a population that is literally eating itself to death. However, my feeling is that it would be better to be a bit more cautious when advising people how much refined fructose they should be eating. For a product that is not essential for health, the risks that is detrimental to health seem significant and some caution appears to be warranted.

  7. If Professor Lustig is right, many others will have been completely wrong. I suspect he is right – and so removing added sugar from our food supply is the obvious low-hanging fruit in any serious anti obesity and anti-diabetes campaign – but time will tell. In the current Australian debate on sugar and obesity, I am disturbed by some of the research being published by academics at the University of Sydney. One of the highest-profile papers on this topic – which concludes that sugar consumption and obesity are largely unrelated – clearly is dominated by major errors. My concerns are documented at

  8. Table sugar is not a food nor is it a nutrient. Until 200 years ago virtually no one ate it. People can and do simply stop eating it.They do themselves no harm and possibly a lot of good. No one seems to be able to point at long term, large population independent studies showing table sugar to be safe in “moderate” amounts. I think not eating any table sugar is a prudent move and I believe foods containing more than 3 or 4% fructose should be taxed. They certainly should be removed from schools entirely and not sold to minors.

    • Thanks Gregory, Julian, Rory and everyone who has contributed to this debate. I would like to summarise the arguments I have presented in recent weeks.
      In an earlier blog I argued that recommended carbohydrate intakes may be too high, as the risk for coronary disease associated with carbohydrate appears to be similar to that of saturated fat. Consequently, eating less carbohydrate would be better and nutritionists really need to focus on which carbohydrate foods are better and worse for health. There is no point in removing ‘good’ carbohydrates from the diet; we should focus on removing the ‘bad’ carbohydrates. But there is currently no agreement among nutritionists about what is good and bad when it comes to carbohydrate-rich foods.
      For me, just focussing on sugar is not enough. The expert reviews on sugar, discussed in another blog, suggest it is fairly benign with respect to the risk for chronic disease (the exception here may be sugar-sweetened soft drinks). Robert Lustig has a different view but it is fairly radical, even among fructose experts. I suggest everyone read the work of these other experts. It is a mistake to think that there is a simple solution to obesity. The ‘just eat less fat’ approach was a disaster.
      The problem with an approach that is solely sugar-focused is that it leads to unintended consequences. In the United States Jamie Oliver waged a campaign against chocolate milk on the basis of its sugar content and this led to the banning of chocolate milk in some schools. Bad outcome. Chocolate milk is a nutrient-rich beverage – a total contrast to soft drink. Nutrient density of foods is another aspect of carbohydrate quality that needs to be considered.
      Another problem with a solely sugar-focused approach is that it assumes that starch is a ‘good’ carbohydrate, which is not necessarily so. Take white rice for example – it’s nutrient-poor and has a high glycaemic index. Currently many health experts are trying to find ways to encourage Asian populations to eat less white rice to (1) increase the nutritional quality of their diets and (2) to limit the adverse metabolic outcomes of high intakes of white rice. White rice is worse than many foods with added sugar yet the general public does not hear this because the world has become preoccupied with sugar.
      We need more sophisticated models of carbohydrate quality. Regards, Bill.

      • Thank you for taking the time to respond. I agree that good nutrition is a lot more complex than simply not eating sugar or fructose and that a lot of other high carb sources provide very little nutrition (eg. white rice & white flour). I will be interested to read your thoughts on carbohydrate quality and will keep a watch out for your future postings on the topic.

    • I suggest that those following this blog consider Rory’s review in the light of the reviews on this topic by IOM and EFSA discussed last week. Make up your own mind. Regards, Bill.

  9. I have been contacted by Robert Lustig who assures me that his motivation is pure: “I am a pediatrician, concerned for the health of the next generation of children. That is my only motivation.”
    Regards, Bill

    • Hello Caren
      So you are sceptical about sceptics – no bad thing. I base my nutrition advice on nutrition science. Consequently I find myself taking a conservative approach on some issues and a progressive approach on others.
      In relation to sugar, a big bandwagon has rolled into town and it’s always tempting to jump on board for the ride. It’s harder to stand your ground and argue that the evidence is not convincing. If the science is sound, nutritionists should support the status quo.
      For the last 30 years the majority of nutritionists have argued that low fat diets improve health (the status quo). Following recent research findings I have been arguing that low fat diets do nothing and that higher-fat, Mediterranean-type diets are better. If the status quo is no longer supportable, we must change our advice. Regards, Bill

      • In Robert Lustig’s article ‘Fructose: The Poison Index’ in The Guardian (21st October 2013) he mentions ” The food industry is fond of referring to a 1999 study showing that liver fat generation from oral fructose occurs at a very low rate (less than 5%) “. Could anyone tell me which study he is referring to? I am analysing the article and have searched everywhere for it! Any help would be much appreciated.

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