Feb 06 2014

Fructose vs Glucose

Health conscious individuals have been systematically informed about how important nutrition is to health. This is no doubt true, nutrition is very important. But the nutrition industry, and “natural” health gurus selling vitamins would like you to think that “nutrition is everything,” (in quotes because I have been told that phrase more than once).

Nutrition is important, but it is only one factor among many affecting health. It is not the cause of all problems, and therefore it is not the solution to all health issues.

The overhyping of nutrition, however, creates an obsession with endlessly tweaking one’s diet in the hopes that the perfect combination of “superfoods” will cure all ills and optimize health. The unstated major premise of such claims is that our bodies perform best within very narrow nutritional parameters. It is closer to reality, rather, that our bodies are resilient to a fairly broad range of nutritional parameters. It is helpful to get the broad brushstrokes correct (do not overconsume calories, have a varied diet, etc.), but obsessing over tiny details is likely to be a waste of time.

In the middle of all this is also the ever-present naturalistic fallacy.

One such detail is the distinction between fructose and glucose – two common forms of sugar. Fructose is the form of sugar most commonly found (as the name implies) in fruits. Table sugar, sucrose, is a disaccharide – a combination of one fructose and one glucose molecule.

For years there have been claims that fructose is worse for the body than glucose, and that high-fructose corn syrups (commonly used in processed foods) is partly to blame for the obesity epidemic and other health ills. This, of course, led to the marketing of products with “all natural cane sugar” containing 100% sucrose (which of course is 50% fructose). High fructose corn syrup (HFCS) typically used in food is HFCS55, which has 55% fructose and 45% glucose.

Yeah, that’s it. That’s the dramatic difference. The reasons for using HFCS55 rather than cane sugar are economical and practical – fructose is actually sweeter than glucose so you can use a bit less of it, it is a liquid so it stores and transports well, and its generally cheaper.

Critics of this “unnatural” product site studies showing that fructose has an adverse effect on metabolism. It does – raising triglycerides, for example – but no more than other sugars. Critics often recommend “natural” alternatives based on no evidence, just the fact that they are natural.

Partly they also rely upon basic science studies rather than clinical studies that look at net health effects. This is a common fallacy – extrapolating from basic science data while ignoring or downplaying the clinical data.

A recent systematic review of that clinical data found:

Pooled analyses show that fructose in isocaloric exchange for other carbohydrate does not increase postprandial triglycerides, although an effect cannot be excluded under all conditions. Fructose providing excess energy does increase postprandial triglycerides. Larger, longer, and higher-quality trials are needed.

Consuming too much of any sugar is bad for you, but fructose no more than anything else. Some of the same authors also just published their own clinical trial, looking at a variety of health outcomes. They found:

Depending on the cardiometabolic endpoint in question, fructose has variable effects when replacing glucose. In the absence of clear evidence of net harm, there is no justification to replace fructose with glucose in the diet.

In other words, some of the parameters followed were a little better for fructose, some were a little worse, and in the end it was all a statistical wash.

The best interpretation of all available clinical evidence is that you do not need to worry about how much fructose vs glucose is in the food you eat, and it matters not at all how “natural” the source of the sugar is. You do need to pay attention to the overall amount of sugar in your diet. Simple sugars are calorie dense and high intake does have an adverse effect on numerous metabolic parameters, including cholesterol and insulin.

In the end, when it comes to nutrition, simple advice is often the best. Just don’t overdo the sweets.

22 responses so far

22 Responses to “Fructose vs Glucose”

  1. DevoutCatalyston 06 Feb 2014 at 11:01 am

    Once upon a time the health food industry claimed that added sugar was a food industry ploy to get people to consume more product. Health food was small time and they hawked bland products to set themselves apart and portray themselves as ethical. Nowadays health food is big industry and they promote their snacks and breakfast cereals by adding sugar to move more product. Makes their stuff taste better. But because they are the ones doing it, this is OK, although formerly, this was not OK. Big Health Food wears the white hat by casting doubt upon the other guys’ ingredients and gaming the system. On current food products we have detailed labels ostensibly to protect the eater from the machinery of chicanery. A health food cereal box today will list “organic evaporated cane juice” as an ingredient. In the 1970s this wording would have been protested as the cynical deception of big industry to soft peddle the added sugar. My how things have changed. Health food industry = laughing hyenas, all the way to the bank.

  2. rezistnzisfutlon 06 Feb 2014 at 11:16 am

    Unfortunately, health and fitness circles, including those who are considered “experts”, are rife with pseudoscience. Admittedly, there were many things even I took on faith some years ago, “gym lore” that was passed on orally and taken at face value because “it made sense”.

    One problem with health and fitness is that there just isn’t much in the way of clinical study surrounding it to make solid conclusions about what universally works and what doesn’t, or what role certain nutrients play. We’ve seen a lot of headway in this in the past 10 years, but it’s just now starting to catch up. The other problem is that everyone has different tolerances and reactions to nutrients, so what may be tolerable for one person may not be for another, which makes clinical study all the more difficult.

    Another issue is with the field of dietetics, which has traditionally been about programming diets for patients who are sick or injured. When this paradigm is extrapolated to healthy people, you run into problems. For instance, programming a diet for kidney patients would be inappropriate for healthy people. I have seen it several times where GPs, and even some specialists, raise alarms when they notice someone has elevated serum creatinine levels in the blood work of a bodybuilder who eats more protein than the average person, and may even supplement with creatine. I’ve seen many dieticians rail against high protein diets (not Atkins, but just higher levels of protein in a balanced diet) because “it’s bad for the kidneys”.

    Many people just assume certain things because someone who seems authoritative tells them, or they inappropriately attribute the wrong thing to someone else’s success. Or, it just “makes sense” to them. Usually, these things have no actual evidence supporting them and is based on testimonial and/or personal anecdotes, which are, of course, the bread and butter of much of the fitness industry.

  3. RoninChurchillon 06 Feb 2014 at 11:30 am

    I agree the whole sucrose vs. HFCS debate is entirely based on misperceptions about what exactly each are. The small percentage change in glucose vs. fructose isn’t going to spell metabolic disaster, even if fructose was a villain.

    I do wonder about the differing rates of CHO absorption of a meal containing only glucose vs. a meal containing both glucose and fructose. Endurance athletes will often take advantage of drinks/bars with a 2:1 mix of glucose to fructose since the mixed CHO allows for faster CHO uptake in the small intestine (due to multiple transporters being utilized), ultimately providing more energy. Glucose absorption alone seems to cap at around 60 g/h, whereas a drink with a 2:1 mix can be absorbed at 90 g/h CHO.

    For anyone consuming healthy amounts of food (i.e., not overconsuming), differing transport rates probably wouldn’t make a difference, but what about for individuals who continually overconsume sweets and foods with high fructose content? Perhaps fructose isn’t by itself responsible for anything malicious, but increasing rate of CHO absorption to 150% of glucose-only levels could make a significant difference in weight gain over time.

    Just a thought. If your diet isn’t high in added sugar you’re unlikely to encounter this problem, so again, it’s not really about fructose being inherently bad.

  4. ConspicuousCarlon 06 Feb 2014 at 11:40 am

    CNN just had a guest article about “added sugar”. The phrase was used extensively, as though adding sugar were a specific entity rather than an act.

    Enhancing that, it contained a statement about the mysterious “added sugar” which went something like “it’s different from naturally-occurring sugars in foods like…” and then went on to list some foods which naturally contain some sugar… including corn, which is really odd to say because CORN SYRUP is the most common sugar added to foods.

  5. ConspicuousCarlon 06 Feb 2014 at 11:52 am

    A health food cereal box today will list “organic evaporated cane juice” as an ingredient.

    [ahem]… “LOLZ”

    Somewhat recently, the corn industry asked the FDA if they could call their syrup “corn sugar” instead of “high fructose corn syrup”, seeing as how 1. “HFCS” has been demonized by propaganda, and 2. It actually IS sugar from corn so it’s not really asking much to call it that.

    Some cranks threw a fit over that as if it were somehow deceptive. Meanwhile, the pseudo-health industry pulls stunts like the above in which they won’t even say that their sugar contains sugar.

  6. BBBlueon 06 Feb 2014 at 2:13 pm

    ”Fructose is the form of sugar most commonly found (as the name implies) in fruits.”

    Actually, fructose is not the form of sugar most commonly found in fruits, if by that you mean it is the dominant sugar among those present. For instance, the relative composition of sugars in many peach varieties is in the neighborhood of 10% fructose, 75% sucrose, and 15% glucose. In other fruits, cherries, many berries and grapes, for instance, fructose and glucose are roughly equal in concentration and there is relatively little sucrose, while fructose is generally the dominant sugar in apples and pears.

    As for relative sweetness, if one sets the perceived sweetness of sucrose to 100, which is the standard for comparison, fructose would score +/- 170 and glucose +/- 75. HFCS would be somewhere in the range of 100-120, depending on the proportion of fructose to glucose.

    A common means of measuring sugar concentration is by refractometer with total soluble solids concentration (SSC) expressed in °Brix, which is roughly the same as %. SSC by refractometer does not discriminate among types of sugar or other soluble solids, so it is just an estimate and not necessarily a reliable indicator of flavor. Relative sugar composition and total content along with aromatic compounds are the variables of greatest interest to plant breeders in their attempt to improve the flavor of fruits.

    Of course, none of the foregoing changes the overall point being made, which again, is spot-on.

  7. TsuDhoNimhon 06 Feb 2014 at 3:42 pm

    For fun … the “Agave Nectar”* that is the sweetener of choice for the anti-HFCS group has a lot of fructose in it. More than HFCS.

    So if it’s the fructose that’s evil, why are they using it? The cute picture of an agave on the label?

    *Marketing genius squashes potential tequila glut. When the acres and acres of agaves that were planted during the big tequila boom finally ripened enough to harvest, there were already warehouses of tequila … so they did the other thing you can do with agave juice and made syrup out of it.

    Cleverly packaged and marketed, it’s ideal for sweetening your kale and breast milk smoothies.

  8. ConspicuousCarlon 06 Feb 2014 at 3:56 pm

    Here’s a chart of some fruits and their sugar types, even though it doesn’t matter:

  9. SteveAon 06 Feb 2014 at 4:07 pm

    DevoutCatalyst: “Nowadays health food is big industry and they promote their snacks and breakfast cereals by adding sugar to move more product. Makes their stuff taste better.”

    So true. When our local health food store opened some years ago it was full of ultra ‘Puritan’ products. No added anything. Shelves and shelves of snack bars made out of what looked like compressed bird seed.

    It apparently didn’t sell that well, because if you go in now, you find the same sort of products except everything is cut liberally with chocolate chips.

  10. Bronze Dogon 06 Feb 2014 at 5:07 pm

    Nowadays health food is big industry and they promote their snacks and breakfast cereals by adding sugar to move more product. Makes their stuff taste better.

    I’m reminded of an old cereal commercial going through the horrible sins of competing cereals followed by reaction shots.

    “Cheerios has added fat.”
    Incredulous woman: “They add fat?

    Well, yeah. Fat tastes good so people will be more eager to eat it. The more people eat, the more they sell. Same kind of rationale for fast food places to make triple baconators. Yeah, it’s an unhealthy, self-justifying vicious cycle, but corporations are in the business of fulfilling peoples’ demands. It’s nasty, but their actions are understandable. It’s not some elaborate evil conspiracy to kill off half the world’s population, just short-sighted greed and gluttony feeding on each other, and a case where the invisible hand of the market goes against our health interests.

  11. tmac57on 06 Feb 2014 at 7:54 pm

    I recall back in the heyday of the frozen yogurt craze,that I took my girlfriend to a non-chain fro-yo shop,where the earnest young man behind the counter extolled the health virtues of frozen yogurt versus ice cream.
    One of his pitches was that theirs was especially healthy because it was sweetened with fructose instead of evil cane sugar. And so it goes 🙂

  12. Will Nitschkeon 07 Feb 2014 at 1:04 am

    @Steven Novella

    Robert Lustig appears to be the champion of the anti-Fructose case. His arguments are rather complex and he does make the point that the diseases that lead to insulin resistance (and other problems) are likely to only manifest over multiple decades. One meta study you cite notes:

    “Most of the available trials were small, short, and of poor quality. Interpretation of the isocaloric trials is complicated by the large influence of a single trial.”


    “Pooled analyses show that fructose in isocaloric exchange for other carbohydrate does not increase postprandial triglycerides, although an effect cannot be excluded under all conditions. Fructose providing excess energy does increase postprandial triglycerides. Larger, longer, and higher-quality trials are needed.”

    Your other study notes:

    “Depending on the cardiometabolic endpoint in question, fructose has variable effects when replacing glucose. In the absence of clear evidence of net harm, there is no justification to replace fructose with glucose in the diet.”

    This second study also examines fewer trials.

    I’m not sure how you’ve managed to reach your conclusion. You can’t actually metaanalyze poor studies – that don’t have the power to answer the questions we want answered – no matter how many poor studies you have – into good science. If you’re going to reach conclusions based on studies like these, let’s just put 100 endocrinologists in a room, get them to give us their opinions on a questionnaire, and whatever their best guesses are can be the ‘consensus’ on the matter. It sure is a lot less hard work than doing some actual good decent research.

  13. rezistnzisfutlon 07 Feb 2014 at 5:01 am


    You base all of your conclusions on the premise that Robert Lustig is correct and assume that it’s fructose that leads to the diseases that lead to insulin resistance. You first have to demonstrate these claims. What makes his case compelling? How is it that fructose leads to disease? How is it that these diseases lead to insulin resistance?

    The point of the meta-analyses isn’t necessarily to justify the consumption of fructose, but to debunk the claims made that fructose causes special harm, or that it is responsible for many societal ills. There is no basis for these claims, and between the cited studies and the basic science, no reasonable expectation that glucose or sucrose is any better or worse than fructose.

    I’ve read Lustig’s work, and it has many flaws with it, primarily by leading with the same preconception that you are, that fructose is bad, then going about proving it without actual clinical evidence to support it. That’s not even science, that’s pseudoscience. Starting with a conclusion then trying to prove it, especially without a posteriori reasoning, is fundamentally flawed.

    Again, you indicate not only that you are little more than a contrarian out to prove us “amateur skeptics” are full of ourselves, but you belie that attitude with your flagrant disrespect for everyone here.

  14. Martin Lewitton 07 Feb 2014 at 5:42 am

    Here is the full text article:


    Note that the longest feeding study was 10 weeks, and the median was 3 weeks. Established effects like raising uric acid and postprandial triglycerides were confirmed.

  15. Will Nitschkeon 07 Feb 2014 at 8:20 pm

    “You base all of your conclusions on the premise that Robert Lustig is correct…”

    I don’t read 99% of the comments posted here but as I wrote the above post I bet my second testicle that one or more foolish individuals would leap to the conclusion that I’m some sort of champion of Lustig’s research. I let my normal discipline lapse and read the first sentence of the very next post, then stopped.

    I’m not prepared to dismiss or accept Lustig’s claims (unlike Steve) because I don’t like to go beyond the evidence and there isn’t enough evidence to decide a matter as complex as this. Yet. Which is actually what the meta studies concluded and not what Steve concluded.

    That’s ultimately the difference between scepticism and activism. Actual skeptics can stay in that ‘uncomfortable’ place in the middle. It’s called agnosticism. When skeptics form groups, committees, etc., hold meetings, lobby on their blogs and so on, they feel they have to create ‘positions’ even over matters where it’s not reasonable to hold a ‘position’. If you’re for ‘X’ your ‘enemies’ must be arguing for ‘Y’ which is the opposite of ‘X’.

    I also want add a general comment because Steve has the habit of dismissing a claim on the basis that there is no experimental evidence in support of a claim. But science is a lot more complicated than that. There is no experimental evidence in support of speciation. However, I accept speciation as highly likely to be true, because there are other types of evidence that is not necessarily experimental in nature which is credible. Obviously if it’s available it’s preferred, but we don’t always get what we want.

  16. rezistnzisfutlon 07 Feb 2014 at 8:46 pm


    No, you don’t get it, we are still practicing skepticism no matter how often you pretend we’re being activists. I HAVE read Lustig’s research, as well as watched his lecture on fructose, and while some of it has science behind it, he draws some wild conclusions about fructose that has little actual evidence supporting them. YOU are the one who is using Lustig’s research as an initial premise for your arguments against fructose. WE, on the other hand, maintain that there is no evidence for the myriad claims made about fructose, including HFCS, considering that the studies actually done on fructose don’t back up any of those claims.

    No one here is making any definitive claims about fructose, glucose, sucrose, or any other simple saccharides. The point of all of this is to debunk the positive claims made about fructose pointing out the negative research, which is pure skepticism. If we were to make unwarranted positive claims about fructose, then we’d be working outside the realm of skepticism. And there is some clinical study, as well as science, to base some conclusion on (namely that there is little differential effect between fructose and other forms of simple saccharides), so it’s unnecessary to be agnostic. We, as skeptics, also understand science, unlike you apparently, in that we realize that science is provisional and further research may indeed yield additional data.

    So it is YOU who is being the activist here, not us. We are practicing proper skepticism.

  17. rezistnzisfutlon 07 Feb 2014 at 8:48 pm

    More accurately, Will, it isn’t activism you seem to be practicing so much as just being contrarian merely for the sake of being contrarian.

  18. ccbowerson 07 Feb 2014 at 10:48 pm

    “That’s ultimately the difference between scepticism and activism. Actual skeptics can stay in that ‘uncomfortable’ place in the middle. It’s called agnosticism.”

    Again, this is an argument to moderation, which you seem to be fond of, but you don’t seem to be aware that this can be a logical fallacy. The problem is that you are viewing this as 2 extreme positions, and envision yourself in the middle. This is misrepresenting the issue.

    There is a fairly common belief (especially among health enthusiasts) that HFCS is less healthy that sucrose, and it is this belief that we should be agnostic to (i.e. it is the default position prior to incorporating plausibility and any available evidence). Let’s keep in mind who is making the claim here.

    “he does make the point that the diseases that lead to insulin resistance (and other problems) are likely to only manifest over multiple decades.”

    This is an appeal to future evidence. OK, well then wait to make those claims when you have that evidence, not before. Let’s start from the evidence and then draw the conclusions, and appealing to future evidence has it backwards. Its fine to have that thought or idea as a possibility for research, but it’s another thing to promote an idea with flimsy evidence

  19. BillyJoe7on 08 Feb 2014 at 12:37 am

    “I don’t read 99% of the comments posted here”
    Pull the first one.

    “I bet my second testicle”
    What happened to the first one?

    “I let my normal discipline lapse”
    Pull the second one.

    “and read the first sentence of the very next post, then stopped”
    Pull the…um…middle one.

  20. faunafarmon 09 Feb 2014 at 7:06 pm

    Usually I am totally unconcerned about fructose in my diet. Until now. I am attempting to find triggers for my IBS using the low FODMAP diet. Part of the diet is to reduce the intake of high fructose foods, although foods with a fructose to glucose ratio of 1:1 are more tolerated. Apparently the fructose can contribute to diarrhea. Here is a quote from the University of Arizona’s Campus Health Service low FODMAP guidelines:

    “Fructose is a carbohydrate found in fruit, honey, high-fructose corn syrup (HFCS), and agave syrup, but not all fructose
    containing foods need to be limited on a low FODMAPs diet. Fructose malabsorption is similar to lactose intolerance, in
    that fructose is not completely digested in the GI tract due to the lack of an enzyme, but unlike lactose intolerance the
    absorption of fructose is dependent on another carbohydrate, glucose. Therefore, fructose-containing foods with a 1:1
    ratio of fructose to glucose are generally well tolerated on the FODMAPs diet and conversely, foods with excess fructose
    compared with glucose, such as apples, pears, and mangos, will likely trigger abdominal symptoms”

  21. Will Nitschkeon 09 Feb 2014 at 11:06 pm

    @Steven Novella

    I want to use another example to clarify the point I’m making. Are carrots healthy? Let’s run a bunch of short studies with small populations to decide that question. Let’s divide people into those who eat carrots and those who are asked not to eat carrots.

    Let’s repeat the above twenty times and do a meta analysis of the findings. How plausible does it sound that people in the non-carrot eating group had worse health outcomes to those who did eat carrots? Let’s speculate that no statistically significant difference in health outcomes was detected.

    Is it therefore reasonable to conclude that removing carrots from one’s diet has no adverse health outcome?

  22. Bruceon 10 Feb 2014 at 2:52 am


    It is reasonable to conclude that you can remove carrots from your diet and still live quite healthily. It is reasonable to conclude from those studies that fear-mongering about the fructose/glucose debate is in fact baseless.

    I know you are trying to prove Steve wrong here, but all you are doing is showing an amazing naivety when it comes to reading and understanding studies and statistics.

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