0 calorie proteins

I remember reading something way back about how all proteins could be either left of right hand wound and that all proteins on earth are wound one way. Our digestive system isn’t designed to digest proteins would the other way and they would be passed through.

Has there been any work done on seeing if we can synthesize this reverse wound protein for use in diet foods?

I don’t understand, what is the point of making a protein just so it can pass through your system? Isn’t tofu “diet protein” in a way? (doesn’t just pass through but it is protein.) I’m missing something.

I belive that, like with certain fat substitutes, it’d have an unwanted effect on your digestive system. The body’s enzymes and such might not work on the reverse proteins and they’d come out like they came in…

Furthermore proteins aren’t a big source of calories. Yes, they can be broken down for energy, but mostly they’re used as building blocks for our muscles and such.

Producing these reverse proteins would probably be insanely expensive too. You’re better off just adding flavourings to something else indigestible, like sawdust.

If they’re completely indegistible, they wouldn’t affect satiety anyway, so what’s the point?

Isn’t fiber indigestible? And doesn’t it affect satiety? Or am I confused?

Nonsense. I defy any protein other than keratin, collagen, or fibrin to stand up to gastric digestion. Left, right, whatever, all globular protein falls before the might of hydrochloric acid and pepsin.

That said, it wouldn’t make sense to reduce the digestibility of protein, because it’s not a major source of calories for most people. I suppose MacDougal dieters who want to reduce their protein load might find it attractive, but it’s easy and sufficient to just avoid meat.

I’ve been told by folks in the know that fiber isn’t entirely indigestible; just that the calories from fiber are much less bioavailable than those from other carbohydrates. IIRC, you get roughly 2 calories per gram from fiber.

Fiber affects satiety by slowing the passage of food through the small intestine, meaning you get a slower release of sugar into your blood. An indegistible protein–say one of the ones on Nametag’s list–wouldn’t have that effect.

The “handedness” (i.e. left or right twist) in Organic Chemistry is called “Chirality”.

Arthur C. Clarke wrote a short story in 1946 called “Technical Error” where a worker in a massive generator had his body flipped into a mirror image due to an inadvertant power surge. It was found that he was slowly “starving” to death due to an inability to absorb key proteins. We need the L-proteins (left chirality) common in nature, but he needed the D-proteins (right chirality).

IANAOC, but my googling seems to suggest that this only applies to proteins. So, as nametag said, stopping the digestion of proteins isn’t helpful to weight loss.

I’ve seen most reccomendations say that we should be getting our calories in a 25/25/50 ratio of fat, protein and carbs respectively.

ultrafiller: I suspect satiety mainly has to do with the act of chewing and swallowing as well as a feeling of bulk in the stomach. By the time the body finds out it’s indigestible, your already away from the table.

Nametag: I believe it’s actually the amino acids that have the reverse chirality, so peptin & ilk would have no effect on them.

naita: I don’t know how you can say they are expensive if nobody has tried to make them. Seeing as we can easily synthesize amino acids in the lab, it might just be a matter of using GM to manufacture some bacteria that can turn those aminos into proteins. If that doesn’t sound too appealing, then it might be conceivable that we could GM a chicken or cow embryo into only using reverse protiens as well and feed it the bacteria chow. You would end up with a chicken breast indistinguishable from the real thing, only with no calories whatsoever.

Nope. Satiety is tied mainly to blood sugar levels. Indegistible food has no effect on that.

Hydrochloric acid is a very poweful solvent, so they would probably be digested.

There’s also a chance that reversed amino acids would really fuck up your body’s natural processes cause they don’t fit quite right.

I dunno, If I eat fast enough, I feel full before my body could possible be reacting to Leptin levels or blood sugar levels. :smiley:

course I get pretty nauseous eating that much too.

There’s a difference between feeling full and feeling satiated, and some stuff out there does digest pretty quickly.

Nah ahh. While acid hydrolysis happens regardless of stereochemistry, proteases like pepsin care very much whether their substrate is D or L.

Even if someone came up with a cheap source of D amino acids, and a cheap method of converting them into polypeptides, you still have to worry about the toxicity of the material. D amino acids tend to show up in things like antibiotics and marine toxins. These are not substances you’d want in your diet food. Keeping them out, and testing for them would raise the manufacturing cost.

Right. Just some GM. No big deal, right? Good luck with that. That’s way beyond our current level of technology. There are probably at least dozens of proteins, and therefore genes, that would have to be completely redesigned from the ground up to ensure we get the same final protein shape from the reverse amino acids, and ensure that those reversed proteins were then able to act on other reversed proteins, etc, etc. We can’t even predict the shape of a normal protein from its amino acid sequence yet.

I’d guess that the number of proteins you’d need to redesign would be in the thousands, plus the tRNA’s and all that stuff too. On the bright side, there is that experiment where someone synthesized HIV-1 protease from D amino acids, and found that it digested the D isomer of the normal substrates.

[Dons tinfoil hat]
Maybe a strict mirroring of all the contents of a cell would work for D protein production?
[/Dons tinfoil hat]

Nah, that’d be too easy!

Not all proteins on Earth are made of left-handed amino acids. Some bacteria do use right-handed (D-) amino acids; these mostly serve to prevent other bacteria from breaking them down. An example is gramicidin, an antibiotic produced by bacteria for self-defense – it contains D-amino acids and cannot be broken down by the protein-destroying enzymes of other bacteria.

Making D-amino acids in the lab is relatively easy-- in fact, most methods of preparing amino acids produce a 50-50 mixture of left-handed and right-handed amino acids, and it’s just a matter of separating out the right-handed ones. Turning these amino acids into a protein that is identical to a natural protein in every respect except chirality is not easy. I think the easiest method would be to use a non-biological process (without involving enzymes), since this is not sensitive to the chirality of the amino acids. As has been mentioned, getting bacteria to make proteins with right-handed amino acids would require right-handed enzymes in the bacteria, so you’d have to redesign the whole system.

Even if it were possible, though, it would have little practical use. Proteins are not a particularly calorie-rich source of energy, and not a cause of concern in obesity. Effective zero-calorie fat or sugar equivalents would be very useful, but zero-calorie proteins (by far the hardest to make of the three) would not do all that much good. Also, if digestive enzymes are capable of breaking down these right-handed proteins (I’m not entirely sure that they can; the enzymes are selective for left-handed amino acids, but you might get some activity with right-handed ones), the whole process will do no good at all. The body has enzymes (racemases) that turn right-handed or left-handed amino acids into a 50-50 mixture of both isomers. Since only the left-handed ones are used in the body, the racemases have the overall effect of converting any right-handed amino acids that might be encountered into left-handed ones.

Fiber comes in two flavors: soluble and insoluble (water soluble and water insoluble). Soluble fiber is digestible to some extent, but insoluble fiber passes through the alimentary canal without any digestion. Each type has its own health advantages. Even though insoluble is not digestible, it does rid the alimentary canal of possible toxins and reduces the risk of colon or rectal cancer. It also provides for greater bulk and more regularity.