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A friend of mine (who previously studied Chemistry and then had a couple of Nutrition courses) claims that all the sugar that does not occur naturally in our food (eg: sugar in chocolate vs sugar in fruit) is "bad".

Specifically, he claims that in foods with added fructose, the spacial arrangement of the fructose molecules is different from the fructose molecules naturally presented in fruit (for instance), and that the "artificial" combination makes it harder for our bodies to process it.

Is there any evidence to support this claim?

closed as off-topic by jwenting, Jan Doggen, Mad Scientist Jul 10 at 10:44

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    There is no such things as "artificial" fructose. Fructose is a molecule and if you arrange it differently it isn't fructose anymore. Even if the sugar, or any other food content, was produced in a laboratory and is "artificially" created if it is the same molecule as the "organic original" it is literally the same and food companys are allowed to call it natural/organic because it is literally the same. You do need to know the difference between sugars and artificial sweeteners because there is a difference. – GittingGud Jul 10 at 9:07
  • @GittingGud he didn't mean in terms of the molecules' componentes, but in terms of spacial arrangement... he said that is where the difference lays! – essay Jul 10 at 9:54
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    Fructose is a monosaccharide, which means that there is no way the spacial arrangement does have impact on the digestive aspect of the sugar. And even if the sugar is a polysaccharide the spacial arrangement does not have impact. Changing the individual monosaccharides of a polysaccharide makes it a new sugar and not a artificial version of another one. I would suggest you do some reading on sugar, but read scientific sources with a chemical basis and not ones that focus on nutrition because thats a field were the experts never agree. – GittingGud Jul 10 at 10:32
  • @GittingGud just as I thought. I would accept that as na answer! – essay Jul 10 at 10:37
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    This really needs a notable source, the answer depends a lot on the exact terms used, and the variants of this I've heard (mostly related to HFCS) are somewhat different than what is claimed here. – Mad Scientist Jul 10 at 10:45
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Your friend is partly correct, but is possibly confused about some things.

The various sugar molecules (glucose, fructose, etc), like most carbon chain molecules have a property known as chirality, and can form enantiomers - essentially mirror images. These are known as D- and L-enantiomers.

Now, sugars produced biologically are D-enantiomers, and almost all enzymes for metabolising sugars can only metabolise the D-enantiomers (although, a bacteria has been found that can metabolize L-glucose). This is because the enzymes that produce the sugars are similarly biased to produce D-enantiomers. Chiral Biological Molecules - University of Texas and How did protein amino acids get left-handed while sugars got right-handed?

Sugar molecules can be created artificially - using processes which will produce equal amounts of D- and L-enantiomers. But our bodies can't metabolise the L-enantiomers, which is how a lot of artificial sweeteners work. low-calorie sugar - NASA Spinoffs

So, artificial fructose is no worse for you then natural fructose - actually, since taste response to L-enantiomers is the same as D-enantiomer, it might be slightly better since you get the same level of sweetness, but only metabolise some of the sugars you ingest.

However, any added D-fructose (and other sugars - natural or artificial) can cause problems simply by introducing too much into our diet. There's a limit to how much sugar we can absorb - and what is not absorbed is metabolised by gut bacteria, causing bloatedness, diarrhea and other issues. L-sugars can also cause diarrhea as the body tries to expel it. Chiral Toxicology: It's the Same Thing...Only Different.

A further confusion is that there's also High Fructose Corn Syrup as a food additive - which is actually a mix of free glucose and fructose. Since glucose is the primary sugar responsible for causing insulin resistance, this may be linked to increased issues such as type 2 diabetes.

For a more complete introduction into sugars and chirality Biomolecules - Institute of Organic Chemistry, University of Zurich

  • you state that 'a' bacteria (i read that as 'one strain of') has been found to metabolize l-glucose, but later you go on to say that r-sugars are metabolized by gut bacteria giving rise to problems. so are there actually a lot of those r- capable bacteria? – bukwyrm Jul 15 at 5:22
  • @bukwyrm I've clarified that section - didn't mean to imply common gut bacteria can metabolise L- sugars - they feed on the D-sugars we don't absorb – HorusKol Jul 15 at 5:27

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