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Why is too much sugar bad for us?

  1. Jul 25, 2010 #1
    These days there's a lot of hype about cutting down on sugar in your diet, and there's all those GDAs and advice about how to reduce your sugar intake, etc, but I can't really find much information about why sugar is bad for you. It seems, from what I've found online, that pretty much the only reasons to cut down on sugar are because of the calories, and because it rots your teeth (and I'm sure causes various other problems in the mouth).

    So assuming you're a healthy weight and take care of your teeth, is there actually any reason to cut down on sugar, or stick to any particular daily amount? I always thought too much sugar could cause diabetes, but I can't find any information to support that - does anyone know if there's any truth to it? Are there any other health dangers from consuming too much sugar?
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  3. Jul 25, 2010 #2


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    Mostly calories, sugar is water soluble so it doesn't really stick on your teeth - potato chips are worse.

    Eat too many calories, don't do enough exercise = get fat.
    The only thing against sugar is that it's empty calories, if you eat vegatables you are getting some calories but a lot of other good stuff, with sugar you are wasting your ration of calories you can eat without gaining anything other than the nice taste.

    There is some evidence that not all calories are equal, some sugars (eg HFCS) cause you to make fat more than other types.
  4. Jul 25, 2010 #3
    So say you were fairly fit and healthy and weren't putting on weight, is it OK to pretty much eat as much sugar as you want as long as you're eating enough of all the other nutrients you need as well?
  5. Jul 25, 2010 #4


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    Because we make it bad for us when we process it (white sugar, high fructose corn syrup) and then we load drinks and snacks up with too much of them.

    Sugar from fruit (glucose and fructose) isn't really that bad

    Milk (lactose) is a different topic. Many people argue that cow's milk is for calves, not humans.
  6. Jul 25, 2010 #5
    I've heard lactose intolerant people say that. Sounds like they're just jealous they can't drink it. The milk from the cow isn't for us, but somehow the meat is? Massacre the cows and eat their flesh, but if you milk the cow and drink it, that's just weird.
  7. Jul 25, 2010 #6
    I find that people that argue that stuff are really missing the big picture anyway. Since when in the last say 10 000 years have humans only been eating things that were 'meant for us'??? I mean we cook our meat and we flavour it... hardly necessary but tastes good. Same with milk... tastes pretty damn good in my books and it's normally got a bunch of other goodies up in there to boot.
  8. Jul 25, 2010 #7
    It depends what you mean by sugar.
  9. Jul 25, 2010 #8
    OK so even if it's processed sugar, why does processing it make it bad for you? And in what WAY is it bad for you?
  10. Jul 26, 2010 #9
    The issue with sugar as it is related to non-diabetics (for whom sugar is an obvious issue of balance) may be that large doses of sugar can cause a spike in insulin production, then a "crash" the pattern leading to insulin resistance (aka Type II Diabetes). This is not a certainty, and some people clearly can pack it in without much consequence.

    For your teeth, as Mgb said, it's starches which stick to your teeth (and poor hygiene) which are the primary culprits. This material is metabolized to simple sugars and all the while it tends to be covering the tooth.

    Finally, sugar is calorically dense and easy to eat. While it's true that fat packs more calories per gram than sugar, you can easily down hundreds of calories of sugar without a feeling of satiation compared to fats. People are often not aware of the volume of simple sugars they consume in processed foods, soft drinks, candies, and food prepared in restaurants, much as is the case with salt. This isn't a strike against either sugar or salt, but how we deal with them.
  11. Jul 27, 2010 #10


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    First of all someone should define what "sugar" is: in non-scientific usage "sugar" = "table sugar" = sucrose. Sucrose is one glucose molecule and one fructose molecule linked together; when it gets into your small intestine the linkage is broken and you get glucose and fructose separately, no different than if you ingested HFCS. In HFCS the gluc/fruc ratio varies, but the most common forms are 55% and 42% fructose so both are more or less the same as sucrose.

    Glucose is not a metabolic issue: every cell in your body uses it for energy, in fact almost all forms of life (even bacteria and archaea) can use it as well. Your brain can use ONLY glucose, BTW, it cannot metabolize proteins of fats for energy the way other parts of your body can.

    Fructose is a different matter. Evidence has been piling up for years that fructose is involved in the "metabolic syndrome" cluster of disorders, e.g. obesity, type 2 diabetes, cardiovascular disease, etc. Fructose also contributes much more to the formation of inflammatory abdominal fats than other sugars.

    Lactose is not a constituent of table sugar. It is composed of glucose and galactose. I have seen some rumblings about potential health problems of galactose but it doesn't seem to be a hot topic. Lactose intolerance can be a problem though, which results from having a mutation in your lactase gene, which codes for the enzyme that splits lactose into its component monosaccharides. The pancreas secretes lactase into the small intestine, but if it doesn't do it's job quick, then your gut flora will start digesting the lactose and producing acids (and CO2), which irritate the intestine causing diarrhea and gas. Taking probiotics or eating predigested dairy products (e.g. yogurt) reduces the problem. But none of these issues overlap with the problems caused by sucrose/HFCS consumption.

    Considering that sucrose/HFCS only has two components, one is vital and the other not, I think that alone should serve as a smoking gun as to which one is the problem, if sucrose is causing problems...

    Here is a good review article (even back in 2005) on the known medical issues surrounding fructose intake:

    Something even more hard-hitting, I think, is a recent video in UCSF's public YouTube channel, by Robert H. Lustig, MD, UCSF Professor of Pediatrics in the Division of Endocrinology -- titled "Sugar: The Bitter Truth". Be prepared for some biochem, but the lecture covers much more ground than that. It provides a very clear argument for considering fructose a toxin -- once fructose hits the liver, the metabolic impact is more or less the same as alcohol -- which explains why chronic alcoholics and heavy consomers of sugar/HFCS wind up with the same health issues down the road:
    Last edited by a moderator: Sep 25, 2014
  12. Jul 27, 2010 #11
    Exactly. Sugar causes a spike in insulin and blood glucose levels, it is quickly digested, within 3 hours after consumption, blood glucose is below fasting level and you feel hungry again. The consequences are twofold. One is that, in the long run, you develop insulin resistance a.k.a. type II diabetes (a very nasty condition). The other is that, since it's absorbed so quickly, you end up feeling hungry sooner, and you're prone to over-eat. Over-eating leads to obesity, which comes with a host of health issues of its own.

    Not so simple. Pure glucose and simple sugars that contain large quantities of glucose are bad for the reasons I mentioned above. Your body is simply not designed to handle repeated, large injections of concentrated glucose. In fact, diabetics are ENCOURAGED to eat fructose, because it does not cause the same insulin response as glucose, it's just processed directly by the liver through a totally different metabolic pathway.

    On the other hand, "high glycemic index" foods, which contain glucose in the form of starch polysaccharides (many molecules of glucose joined together), are gradually metabolized to release glucose, and therefore they are much gentler on the body.
    Last edited: Jul 27, 2010
  13. Jul 27, 2010 #12


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    You are correct that refinement + overconsumption are the real problems here, almost regardless of the sugar. I was pointing out the orthogonal argument that glucose per se is not an issue, but it can be argued that fructose, in any quantity, is problematic. True, it's only a small problem in naturally occurring foodstuffs and we have evolved to handle naturally-occurring fructose loads. But we have not yet evolved to handle all the things we do with our modern food supply, esp. overloading them with refined carbs, and right now a lot of research is pointing to fructose in particular.

    That is no longer the case. Initially it was thought that fructose would help diabetics, but research has scrapped that idea. While fructose does not cause insulin spikes, it is currently contraindicated for diabetes because it raises triglyceride levels and fails to stimulate leptin production, so you lose the satiety response and tend to overconsume. This is due in part to the fact that, as you pointed out, only the liver metabolizes fructose. Broadly speaking, if your liver is the only organ that processes compound X, then compound X is a problem for your body...

    Fructose does not contribute to glycemic load, but triglyceride and VLDL production increase. This is because the liver produces fat for storage, and the amount of calories converted to fat is -- correct me if I'm wrong -- a function of energy load as experienced by the liver, more specifically the "acetyl-CoA load", which the fructose pathway provides a back door to. A glucose load will be absorbed by many tissues as it moves through the bloodstream, lowering the load on the liver. A fructose load will go directly to the liver alone, saturate the TCA cycle and spur storage of the excess acetyl-CoA as fat.
  14. Jul 27, 2010 #13


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    Just read my own post. I might sound like a glucose apologist :rolleyes:

    Just wanted to say I'm not... Overconsumption of calories is not healthy, and in particular, consuming refined glucose or starch also causes insulin spikes, which lead to resistance and eventually type 2 diabetes. But I think a lot of people think that the problems with "sugar" end there, weight gain / diabetes / cavities. So if a product comes out that doesn't have "sugar" (but HFCS instead) then great! We're off the hook, right? No -- the fructose side of the problem is well documented in the literature -- but not in the media. So I wanted to bring extra attention to it.

    The media got around to condemning fats (generically), then carbs (generically), and now it's slowly turning on to refined sugar (even though negative research has been around for over 70 years), but with all the talk about excess calories => problems, we have been missing the fact that a calorie is not just a calorie. 100 calories from glucose, fructose, protein, saturated or unsaturated fats all come with different side effects, and some sources are far quicker at causing problems than others. I don't think most people realize that fructose, calorie for calorie, is much more likely to cause weight gain than is glucose, both because of its metabolism and because it can't make you feel full. And table sugar has the distinction of dosing you with refined glucose AND fructose simultaneously.
  15. Jul 28, 2010 #14
    I wouldn't bother drinking diet soda, or nutri-sweet instead of table sugar. I would just consume less of it. A good natural sweetener to use is stevia.
    Last edited: Jul 28, 2010
  16. Jul 28, 2010 #15
    Fructose can't make you feel full (lack of leptin production), but glucose can actually make you feel hungry prematurely (blood glucose overshoot) and it also raises insulin levels, which stimulates lipogenesis. So they are both dangerous in large quantities as part of a steady diet. It's hard to say which is worse. I haven't seen any studies on humans that conclusively say that one is significantly more likely to cause weight gain than the other.

    And it's all mostly theoretical, since most realistic simple-sugar products, from table sugar to HFCS to grapes, will contain generous amounts of both glucose and fructose.

    There's no scientific reason why you shouldn't abstain from both glucose and fructose altogether, and stick to starches. My own ancestors probably lived on starches 10 out of 12 months a year for many centuries, only enjoying occasional apples or cherries when in season (July to September) ... From the evolutionary standpoint, it's beneficial to gain weight as long as you don't do it year round.
    Last edited: Jul 28, 2010
  17. Jul 29, 2010 #16
    OK so having re-read this thread and tried to explain it to a friend, it seems that a recurring theme is that 'refined' sugar is bad for you, much more so than naturally occurring sugars. So I was wondering if someone could explain to me what is actually meant by the term 'refined'. Why is refined fructose worse than natural fructose? And what on earth is the difference?
  18. Jul 29, 2010 #17
    By refined we mean concentrated. Some foods (fruit juices, in particular) naturally contain concentrated simple sugars, they are NOT better than stuff that's been artificially sweetened with sugar or HFCS.
  19. Jul 29, 2010 #18
    The basic rule is that the more steps it takes from FOOD X -> Glucose is "better", for the reasons discussed regarding the "whiplash" effect on insulin and blood sugar. The refinement process itself is not the culprit, and in some cases is a life-saver. There is a reason that diabetics often have a tube of pure glucose around, because short of an IV infusion of glucose, it's the fastest way to get "sugar" in its usable form into the body. A slice of bread is going to end as, in part, sugars, but it takes many more steps.
  20. Jul 29, 2010 #19


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    Here's how I like to think about it. When eating "natural" sugar rich foods like fruits, you get the sugars (bad for you) along with some of the chemicals contained in the fruit that are good for you (e.g. vitamins, fiber, antioxidants, etc.). With refined sugar, you take all of the bad parts of these foods (the sugar) while throwing out anything in the foods that are actually good for you. It is similar to a comparison between wheat bread and white bread. White bread is wheat bread minus the healthy parts (fiber).

    My take, without getting into so much details about exact sugar composition, is that 1 cal of sugar is equally bad whether it is from a fruit or from high fructose corn syrup. The difference is that the 1 cal of sugar from fruit comes with some amount of good nutrients while the 1 cal of HFCS lacks any other redeeming value.
  21. Jul 31, 2010 #20


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    Let's keep this thread on topic and show some actual evidence for the claims made. We can't tolerate pure speculation.
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