"Left-handed" sugar

Factual Questions
1

About ten years ago or so, I read in one of those “developments to watch” science and technology columns that a scientist had developed a sugar substitute that amounted to a mirror image of a regular sugar molecule. The idea was that the taste buds would recognize this as sugar, but the digestive system would be unable to process it, so it would pass intact from the body.

Does this sound familiar? Did anything ever happen with this? Everytime I’ve heard of a new sugar substitute, I’ve looked up the details to find out if this is the same thing, but none of them appear to be. Most of the sugar substitutes have some drawback (can’t be used in baking, bitter aftertaste, might cause cancer, etc.) but this sounded ideal.

2

Yes, I remember hearing about this too. But like you, I haven’t heard what became of it. I too would like the straight dope on this.

3

I heard about 6 months ago on UK TV that they’d finally created this, and it was perfect.

Unfortunately, I don’t know who “they” are… But I have the impression that it had been bought by one of the major sweetener manufacturers.

4

I sure hope a GI doctor latches onto this question. Seems to me that sugar molecules passing unmolested through one’s body could be a bad thing. Like in the kidneys, maybe?
Peace,
mangeorge

5

One of the problems has been cost effective commercial development. A company called Spherix (formerly Biospherics) has been trying to do it for some time now, but are now pushing something called D-tagatose:

http://www.foodtechsource.com/emag/017/trend.htm

They are stating that the D-tagatose has the same benefits - it tastes like sugar, but simply isn’t digested. It also occurs naturally, and can be produced economically. The company blurb on it, which they are marketing under the name naturlose:

http://www.tagatose.com

Pepsi is going use the stuff in a new Pepsi-flavored Slurpee drink at 7-Eleven’s, according to an August press release.

6

Lotsa things pass thru the GI tract unmolested, mangeorge. They don’t go anywhere near the kidneys. Olestra, the fake fat is the first one that comes to mind.

I hope the sugar isn’t able to be digested by bacteria (which would produce lotsa gas). I suppose it could cause an osmotic diarrhea if taken in large concentrations though, and make olestra’s anal leakage warnings seem like small change.

We’ll have to wait for clinical trial data.

7

Oh.
So the sugar has to be digested (metabolized?) before it can get into the blood and be dumped by the kidneys? I ask because one test for diabetes is a urine test. If it’s high they say you’re pissing a lot of sugar. This stuff would be a boon for diabetics.
I’m always cynical, 'cause we seldom get something good without paying some kind of price.

8

Kidneys filter blood. There is no direct channel from the intestine to the kidneys. The intestines absorb stuff into capillaries, send it to the liver where much stuff is done, to the heart, out the aorta, then thru the kidneys.

9

I think Mangeorge has a point though Qadgop. Monosachharides don’t need to be acted on by enzymes to pass through the gut wall. They just get pased though intact. In fact conversion of complex carbohydrates into monosacharides is how they are digested. I don’t know exactly what the mechanism is for glucose absorption on the gut, but if the transport system can latch onto L-glucose then it’s gonna get passed inot the bloodstream.

Once it’s in the bloodstream it’s got to be disposed of. Since it’s resistant to enzymes the kidneys are going to be charged with disposal. That can’ be good in large quantities, as Mangeorge says.

10

I followed yabob’s tagatose link above. They (the company) claim that not only is the product harmless, but that it is even beneficial for non-insulun dependent diabetics. There’s a research paper which I’ll read later.
A couple more developements like this, and we won’t even need smarty-pants doctors. :wink:

11

I missed mangeorge’s point earlier, when he asked if the stuff needed to be digested to enter the system. I was operating under the assumption that the stuff was not absorbable at all. If that’s not the case, then my statement is irrelevant. My bad.

12

I forgive you, Qadgop.

13

The tagatose-D is claimed to be “prebiotic” which seems to indicate that it isn’t digested (definition: “a nondigestible food ingredient that affects the host by selectively targeting the growth and/or activity of one or a limited number of bacteria in the colon”).

Spherix also claims:

Spherix is making an awful lot of beneficial claims for this stuff, for just an oddball sugar:

http://www.tagatose.com/naturlose-benefits.htm

If you didn’t follow through the interview, this relates to the OP in that the company was trying to commercially develop left hand sugars such as L-glucose and L-fructose, and finding them way too expensive to produce. They realized that this D-tagatose, which occurs in low concentrations in natural sources, rather structurally resembled L-fructose, and they thought it might work the same way.

14

Are these the same as levulose, or is that different?

15

In which case, it could also make a difference as far as phrase and fable; the expression “sharp as rat st" will simply become "sharp as st”.

Aggh. I hope not…

16

Actually, d-mannitol, a regular (dextrorotary) sugar that is poorly absorbed by the human gut when administered orally was (and is) widely used to make dietetic candies and to a lesser degree as an artificial sweetener. It’s also used as an osmotic agent in strokes and brain trauma because it doesn’t pass readily out fo the bloodstream (when administered IV). These ‘diabetic candies’ are not terribly popular these days in the US, but they’re still sold. In other contries they are quite popular.

There is absolutely nothing novel or difficult about producing levorotary sugars, which have ben known for abotu a century. It’s just we’re accustomed to the cheap availability of the d-forms, which are produced in all common plants to some degree. It’s a matter of profit margin more than anything else. You can’t charge nearly the usual “per milligram” pharmacological prices for a sweetener, when sucrose runs a buck or so a pound. In general, sweeteners are chosen that are much sweeter than sugar, so they can be diluted with cheap sugars after they’ve been purified to FDA specs. Sadly, even aspatame and other ‘sugar substitutes’ often adulterated with less-absorbable sugars and sugar-starch compositites to make the “spoonable” granular version (vs the packet powers and tablets). It is right there on the ingredients label.

17

Levulose is the same as fructose. It’s one of the simple sugars. The name “levulose” comes from the fact that polarized light passing through it rotates to the left. Levulose is not a left-handed, indigestible sugar.

BTW, dextrose is the same as glucose, and is another simple sugar. Dextrose rotates polarized light to the right. A dextrose molecule combined with a levulose molecule produces sucrose, or common table sugar.

18

Trouble is, these other substitutes don’t act like sugar. Try making a caramel sauce (ie sticky buns) with Equal. They even suffer a little in hot coffee. I don’t use much sweetner, so I’d be willing to pay more for a true substitute.
Next: Left handed pasta.

19

While we’re here, what about Sucralose, aka Splenda?

20

Jeff Lichtman: I was going to mention that, but I see you got to it first… =) Carbohydrate stereochemistry is my very least favorite part of chemical nomenclature. I am also of the opinion that Emil Fischer’s vast contribution to organic chemistry is entirely negated by his insane and confusing method of drawing molecules.

Anyway…D-tagatose is a ketohexose (6 carbons, with a C=O group at the second carbon, as opposed to aldohexoses, which are aldehydes with -HC=O on the first carbon). D-fructose is also a ketohexose. The difference between them is the configuration of the -OH group at the fourth carbon. D-Fructose is sweeter than glucose, and is the sweetest common sugar; it’s possible that D-tagatose is also sweet.

All sugars, if I remember correctly, eventually must be changed into D-fructose to undergo glycolysis (carbohydrate metabolism). Humans do not have any enzymes capable of changing D-tagatose into D-fructose, so they cannot metabolize it. Apparently, some bacteria, including E. coli and some other common bacteria, do have enzymes for metabolizing D-tagatose as part of their pathway for digesting lactose. Thus, I would imagine that D-tagatose would be digested in humans by the intestinal flora, probably with no nutritive value to the host.

Strangely, it appears that ‘left-handed’ (-)-glucose/L-glucose/l-glucose really is as sweet as (+)-glucose/D-glucose/d-glucose. Assumedly, the same thing is true of the ‘left-handed’ form of fructose (which would rotate polarized light to the right, but would be L-fructose…carbohydrate stereochemistry is profoundly confusing like this!). But it couldn’t be recognized by the enzymes which digest sugars in your body (except possibly by some bacteria), and therefore would have no nutritive value.

I say strangely because there are many examples of two enantiomers having very different tastes and smells. The classic example is carvone; (+)-carvone smells like caraway seeds, (-)-carvone smells like spearmint. Another example is aspartame itself; aspartame is made from two L-amino acids and is much sweeter than sugar. The enantiomer of aspartame, made with D-amino acids, is extremely bitter.

Some references:
I found a good introduction to carbohydrate nomenclature here. (There’s a mnemonic for the names of the aldohexoses, including glucose: All altruists gladly make gum in gallon tanks. It was first suggested by the inventor of napalm.)

There’s a discussion of this topic from another site here.