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Ask Chris: Is Fructose Really That Bad?

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Paul from Facebook asks:

What are your thoughts on fructose? Is it really as bad as Paleo is making it out to be?

Dr. Robert Lustig has worked hard in recent years to demonize fructose, and his efforts have paid off. His YouTube video “Sugar: The Bitter Truth” has over 2.5 million views as of this writing. Lustig et al. claim that fructose is a uniquely fattening poison (when compared to glucose) that is as toxic to the liver as alcohol.

But is this true? Does the current evidence support this position? I’ve changed my views on this over time as I’ve become better acquainted with the literature, so I’d like to share my current understanding with you.

When it comes to fructose, calories matter

There’s no doubt that refined sugar – including fructose – can be problematic. But studies suggest that this is only true when calories are in excess.

This may be the most dangerous aspect of refined sugar: it leads to unintentional overeating. In a recent post on fructose, obesity researcher Stephan Guyenet points out that most people in these studies aren’t deliberately overfeeding. They are inadvertently overfeeding because they aren’t spontaneously compensating for the calories added to the diet via a large fructose- or glucose-sweetened beverage.

This doesn’t happen with fruit or other whole foods that contain glucose or fructose.

When people add fruit to their diet, they reduce their calorie intake elsewhere to compensate. Not so with liquid-sweetened beverages like soft drinks.

When people add a soda or two a day to their diet, they tend not to reduce consumption of other foods, and thus their calorie intake increases.

This is where fructose does appear to be more harmful than glucose. Although people don’t compensate for calories added via glucose or fructose, the fructose-sweetened beverages have more serious metabolic effects.

Is fructose uniquely fattening?

Dr. Lustig argues that, when compared to glucose, fructose is uniquely fattening. He claims that fructose is the most efficient substrate for de novo lipogenesis (DNL), which is the process by which the liver converts carbohydrates to fat.

However, Dr. Lustig relies on animal evidence that doesn’t apply to humans. There’s a big difference between mouse carbohydrate metabolism and human carbohydrate metabolism. When mice are on a high-carbohydrate diet that doesn’t provide excess calories, it’s common to see DNL rates of 50 percent and up. In other words, they are efficient at converting carbohydrates into fat, even when they’re not overeating. (1)

But in humans on an isocaloric diet (without excess calories), de novo lipogenesis falls into the range of 10 to 20 percent. The conversion of carbohydrate is less efficient in humans than it is in mice.

The research in this area is robust and uncontroversial. Nearly 50 controlled feeding studies have been performed on various aspects of cardiometabolic control. Most investigators working in this field believe that DNL in humans is negligible in response to fructose, and doesn’t comprise a significant source of dietary calories.

There’s another problem with extrapolating the animal evidence to humans in this case. The mice in the studies Lustig cites are eating huge amounts of fructose: up to 60 percent of total calories. You’d have to drink more than four 44 ounce Super Big Gulps a day to get that much fructose. Ain’t gonna happen.

According to researcher Dr. Sievenpiper in an interview with science writer David Despain at Evolving Health, the 50th percentile intake for people in the U.S. is 49 grams per day, which works out to 10 percent of total calories. Even the 95th percentile intake of 87 grams per day doesn’t exceed 20 percent of calories. That’s a lot of fructose, but it’s nowhere near the 60 percent of calories fed to mice.

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Is fructose an evil toxin?

Dr. Lustig refers to fructose is a “poison” that is nearly as toxic to the liver as alcohol. But again, human evidence doesn’t support this claim.

In a recent paper, Dr. Luc Tappy and colleagues labeled acetate, fructose and different metabolites with stable isotope tracers so they could see how fructose is metabolized in the human body. (2) They found that 50 percent ends up as glucose, 25 percent goes to lactate and greater than 15 percent goes to glycogen. The remainder is oxidized directly (to CO2 through the TCA cycle) and a small portion – as low as 2-3% – is converted to fat via de novo lipogenesis.

Glucose and glycogen are easily processed by the body, and 2-3% conversion to fat is not significant. And while some have claimed that lactate may be problematic, a paper published more than a decade ago contradicts this. (Hat tip to Evelyn from CarbSane.) According to the authors:

The bulk of the evidence suggests that lactate is an important intermediary in numerous metabolic processes, a particularly mobile fuel for aerobic metabolism, and perhaps a mediator of redox state among various compartments both within and between cells… Lactate can no longer be considered the usual suspect for metabolic ‘crimes’, but is instead a central player in cellular, regional and whole body metabolism.

Translation: lactate from fructose isn’t a problem.

What does this mean for you and fructose?

Fructose-sweetened beverages like soft drinks and juice cause metabolic problems when calories are in excess, and studies have shown that people are not likely to compensate for the additional calories they get from such beverages.

This is why soft drinks and other beverages sweetened with fructose aren’t a good idea. That said, an occasional glass of fruit juice within the context of an isocaloric diet is unlikely to cause problems – unless you have a pre-existing blood sugar issue.

I don’t think there’s any basis for avoiding whole fruit simply because it contains fructose. As I’ve shown in this article, there’s nothing uniquely fattening or toxic about fructose when it isn’t consumed in excess. And since whole fruit contains fiber and other nutrients, it’s difficult to eat a lot of fruit without simultaneously reducing intake of other foods.

Fruit has been part of the human diet for longer than we’ve been, er, human. We’re well-adapted to eating it, and capable of processing the fructose it contains. (Unless you are FODMAP intolerant – but that’s a different issue entirely.)

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315 Comments

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  1. Ideally, we would combine fruit with greens for balance and to avoid blood sugar spikes. Today I blended orange and pineapple pieces with water and had a cup of that with about
    1 1/2 tsp. barley grass powder. Of course, we can also blend fresh greens with fruit.

  2. You can’t have “an isocaloric diet”. Isocaloric means “having the same number of calories”. The word only makes sense if you are comparing two or more diets. The concept is relevant to the debate about whether a low carbohydrate diet causes weight loss only because it makes you eat less calories, or even when compared to an isocaloric higher carbohydrate diet.

  3. This all seems very reasonable, and I always applaud Chris’s scientific look at the research, but I am a little surprised to see no mention of this in an ancestral health context.

    I used to eat a lot of fruit (and grains and sugar). I’ve dialed way back on the fruit, mainly now some berries in a typical week and whatever little scraps of various fruits there are left over after one of their meals (which means on the order of barely a bite of a peach or pear or apple). I’m open to the idea that I could be eating more, but do wonder what the essential value of it is to me, especially in the context of evolutionary biology.

    The way I see it, there were very, very few cultures that got to eat fruit on a daily basis the way it is recommended by mainstream nutritionists in the modern era. My ancestry in particular is northern European. Seasonal fruit was more the norm, and with that there’s also a reasonable argument to be made that its main utility there was to put on a little extra insulation for the bleak months of winter.

    So great maybe fructose isn’t so bad for me as some quarters suggest (or maybe it is; I had fatty liver and metabolic syndrome before going Paleo). Maybe it shouldn’t be on the “avoid as much as possible” list. How much then? “Everything in moderation,” is of course not a terribly useful measure.

  4. Fruit makes me hungry full stop (period). I used to think it was my imagination. If I have it now it has to be in combination with fat and protein. My food addiction was actually a fructose addiction. I think it does affect peoples’ brains differently.

  5. Hi Chris, I’d be interested to hear your thoughts on this http://www.abc.net.au/radionational/programs/healthreport/the-obesity-epidemic/3240406 from Dr Robert Lustig
    (Professor of Pediatric Endocrinology University of California) – essentially some compelling research that unintentionally uncovered some interesting effects fructose has on signals telling the brain when enough food has been eaten and also another interesting side effect of incorrect signals for low energy levels that result in abnormal lethargy and significant discomfort when exercising.

  6. Agree Chris, fruit has many nutrients vs the so called bad fructose. Rather have a fruit than an alcoholic beverage ,that’s for sure.

  7. There are two main ways (I’ve found) to eliminate/reduce the gout/sciatic nerve pain. There are 5 cell types that have no natural ability to shut off intake of excessive amounts of glucose… and most other sugars. One of these cell-types are neurons.
    TRICK ONE ::: vitamin C shares the same transport mechanism as glucose to cross the blood-brain barrier To restrict excess glucose from entering nerve tissue AND REDUCE PAIN, eat some vitamin C (to limit spiking)
    TRICK TWO ::: The brain operates quite well on the fuel ketones. SO GLUCOSE AND KETONES ARE BOTH ‘NATURAL’ ENERGY SOURCES. The strategy to eliminate cancer (& used by diabetics) is to stress the natural saturated fats to create a state of ketogenesis. In this state ketones (instead of glucose) is employed as the sole energy source for cells. Cancer cells, cannot survive without glucose as their fuel.
    To severely restrict carbohydrate (sugar) intake in the a.m. until 3p.m. >>> exercise strenuously >>> pig-out with loads of carbs to purposely cause a spike of cortisol/insulin to cleanse arterial plaque, (etc). The effects of this ‘spike’ is soon over. And will not disturb sleep, if eaten 2 hrs before bed. The technique is called Carb Backloading was introduced by John Keiffer for bodybuilders. This technique should also be very useful to mitigate nerve pain from a sugar overload.

  8. It’s been a while since I watched “Sugar: The Bitter Truth” but I don’t remember thinking “I shouldn’t eat fruit” after watching it. I remember thinking this is a really good message for soft drink consumers to hear.

  9. My daughter and I have both noticed a difference in soft drinks (which I don’t drink anymore, thank you). I sip a sugar sweetened drink, put it down, and I’m done. With high fructose corn syrup, I gulp it down and reach for another. I don’t know if there are other differences, but these is a difference.

  10. I recently discovered Dr Ray Peat, and, like many of his writings and interviews, this article in particular has thrown my world view into disarray: http://raypeat.com/articles/articles/sugar-issues.shtml
    I would most appreciate anyone’s insights into the research Peat has cited in this article (preferably, down to the minutiae). Chris’s article on fructose has made me more receptive to Dr Peat’s ideas, but I still feel like I’m floating in limbo between ‘Fructose is poison’ and ‘Fructose is the ambrosia of the Gods’

    • Aaron,
      I thought that we offered a balance appraisal of fructose http://www.nutritionandmetabolism.com/content/pdf/1743-7075-10-45.pdf
      But an important point is that we don’t know that much about metabolism, any metabolism. We know a lot compared to 100 years ago but there are major missing pieces. I usually describe metabolism as like American football where many things are going on and you can follow the quarterback but that may not be the key to the play. I have not read all of the 8,000 Ray Peat wrote but he and others have presented key plays, highlights if you like, but in many case, we still don’t know who won the game.

      On your question, though, fructose is not a poison and I have had chocolate mousse that has transcendent quality but why expect such extremes?

      Support your local biochemist.

  11. Thanks NSku for your comments. I find it easy to see the 2 categories: fructose with naturally occurring fiber vs. fructose without fiber (as a food additive).

    I would also caution anyone taking supplements including children’s multivitamins who is also concerned about fructose to read the inactive ingredient labels. I was surprised to find fructose in my child’s Child Life multivitamin which is what prompted my search that led me here. This is a helpful discussion. Thank you all and blessings

    • Well people shouldn’t be taking vitamin supplements at all unless they have a deficiency and then the best option is to address that via food if possible.

  12. Jamal, fructose is more reactive than glucose but there is almost never an equivalent mount of fructose in the blood. Fructose is cleared rapidly while glucose is maintained at constant levels. Most glycated hemoglobin comes from glucose. This whole discussion follows from the opinion of Rob Lustig who is not a biochemist and whose obsession does not follow from any great new experiment. He just got a bug in his ear some time and with his superficial understanding of biochemistry became a zealot.

    We all see that kids have too much availability to sugar and we see just the way Lustig sees it. We all know it is hard to regulate kids intake of sugar but it is also hard to regulate their intake of starch and it is hard to do get your kid to go to bed on time. But fructose is not a poison. It is not addictive in the way that cocaine or alcohol are. We know that bananas don’t hurt us unless we put them on peanut butter and banana sandwiches and eat too many. For many things, starch may be worse than sugar — diabetes for example. The science says that reducing carbohydrate is therapeutic if you are overweight or have diabetes. If you think that it is because of the fructose, cut that out first but if you take out fructose and put in glucose, you are just gambling and you don’t even know if the odds are in your favor.

    Support you local biochemist.

  13. I read somewhere that fructose is ten times more reactive in producing glycation products with haemoglobin than an equivalent blood concentration of glucose. Is this true?

  14. Fructose is not metabolized in any way like alcohol. It is a gross exaggeration to say ” it is more likely to promote weight gain and contribute to metabolic syndrome.” If you maintain a high total carbohydrate intake, fructose may be worse than glucose but effects are small. We covered human trials in our review which provides a balanced perspective: http://www.nutritionandmetabolism.com/content/pdf/1743-7075-10-45.pdf

    Support your local biochemist.

  15. The problem with fructose isn’t that it gets converted to fat…the problem is that it is metabolized by the liver (like alcohol) and this process creates toxic metabolites and can harm the liver, potentially contributing to fatty liver disease.
    Every human trial I have read comparing glucose to fructose in isocaloric settings has concluded that fructose is more harmful – it is more likely to promote weight gain and contribute to metabolic syndrome. I did not see any of these human trials covered in this article, there’s really nothing convincing written here. The only thing I agree with is that studies show that fruit consumption does not have the same harmful effects as added fructose.

  16. I’m a bit late to the conversation, but I’ve gathered from reading the article and browsing the comments that I don’t need to be worried about the fructose in my 4 year old daughter’s multivitamin. We don’t have soft drinks in the house, rarely have sweets and when we do, there is a limit on how much.

    Am I on track? Thx

  17. I agree that Fructose is evil for liver more than alcohol . I am a 25 yr old non-alcoholic ( not even a drop of alcohol till now) , but recently i was diagnosed with grade-2 fatty liver. My liver is enlarged by nearly 20% . At the same time i am over weight , no exercise and is a sweet-holic .

    I stayed off alcohol to munch on sweets thinking they are safer but i was wrong . Now i have been asked to cut down on all sweets and fried items.

    Hopefully i will be able to shed my weight and save myself

  18. Chris. I avoid fruit mainly because it interferes with my ketosis more heavily than other carbohydrates.

    I compete in boxing and find my energy level to be better when I’m keto-adapted. Am I missing out on anything by taking fruit out of my diet?

  19. I have a quick question- Are blended fruit/vegetable smoothies okay? I usually eat a fruit+veggie smoothie with whey protein powder for breakfast.

  20. Hi, I have been trying to research agave syrup and whether or not it is an ok alternative to refined sugar. And where it stands next to honey. I am confused by this post because of the previous post (2010) about the 3 causes of obesity, which said that fructose was one of the causes and should be avoided. Can someone please clarify?