Are all acids the same?
January 22, 2010 1:16 PM   Subscribe

How can Prelief react with food acid but not with stomach acid?

"Prelief" is a pill or powder, containing calcium glycerophosphate, which prevents certain foods from causing heartburn for people who are susceptible to that. It does work; if I take two tablets before eating spaghetti with tomato sauce, it doesn't bother me a bit, although otherwise it's a problem. Prelief is also used for preventing food-associated problems for people who suffer from interstitial cystitis (previously); various sources blame unspecified acids in foods for causing bladder discomfort in those people (even foods that make the urine less acidic, such as orange juice, which is known [PDF] to increase the pH of urine).

The makers claim, "Prelief is the only acid fighter that takes out food acid while leaving your protective stomach acid untouched. [Their emphasis.] Prelief takes the acid out of coffee, tomato sauce, fruit juices, wine, and many other of your favorite foods."

This raises several related questions: how can it neutralize food acids in the stomach, without neutralizing stomach acid? Does it neutralize only specific acids that are common in foods? If it's just a question of not taking too much Prelief, how would that be different from taking just the right dose of a calcium carbonate antacid such as Tums?

Also, and more perplexing to me: how can neutralizing acids in the stomach help someone's sensitive bladder? If food acid in the stomach causes bladder problems, why doesn't the hydrochloric acid naturally in the stomach do the same thing? Are all acids a problem, simply because of the fact that they are acids, or is it just that certain irritating substances are being lumped together and labeled 'acids'?
posted by Ery to Health & Fitness (10 answers total)
I have no clue, but my guess is that they chose that chemical because it doesn't react with (or as much with) the stomach acid, but will neutralize other acids.

Similarly, the body has a mechanism for neutralizing the HCL in the duodenum, but (I would imagine) does not neutralize other acids as well.
posted by gjc at 1:29 PM on January 22, 2010

You get heartburn not because of acids contained in foods, but because your stomach secretes more HCl when those foods arrive. Your antacid of choice does not neutralize acids, but simply creates a buffer solution.

Basically (!) if you insert an anion of a weak acid like glicerylphosphate (or citrate, also very popular in heartburn remedies) in an acid environment, if captures H+ ions recreating the original acid (citric acid, glicerylphosphoric acid...) which is way weaker than HCl, so in an acid environment as your stomach it stays combined instead of releasing H+ ions. This is called a buffer solution because it 'buffers' the acidity, preventing the pH to descend below a certain value until there are available (ie: not recombined) anions.
posted by _dario at 1:41 PM on January 22, 2010

(so, no: not all acids are the same; HCl secreted by your stomach is a strong acid, meaning that in solution it is completely divided in H+ and Cl- ions, whereas glicerylphosphoric acid is a weak acid: in solution about 1 in 60 molecules gives off an H+)
posted by _dario at 1:47 PM on January 22, 2010

Much of this makes no sense. Stomach acid isn't "protective" in any way. I'd even call it the opposite given it's damaging properties on it's own and how it activates the natural proteases in the stomach, the only thing stopping all the digesting the stomach away is the mucus layer. It's also not some special magical thing, it's just HCl, the same as any other HCl. There are pretty good feedback mechanisms to keep acidity levels high too, tums don't work because the stomach just produces more acid to override their buffering capacity (and this would be no different).

Overly acidic foods do cause heartburn in some people, me included, because it irritates the lining of the stomach to cause increased HCl secretion and/or irritate the valve at the top of the stomach to trigger reflux. But then many of those foods have proteases in them to which are probably the true culprit in at least some cases, and I can certainly eat some very acidic foods with no problem at all. The orange juice leading to alkaline urine is kind of interesting because orange juice is actually pretty acidic and is on my list of reflux triggers, so I don't know what's going on there (presumably something downstream in the biochemistry since food doesn't go straight from the gut to the bladder).

An acid/base neutralising reaction will happen the same regardless of where the acid is from. What happens will be dictated by the organic chemistry, strength of each solution etc, and food acid vs stomach acid is meaningless. gjc's last point about the intestine neutralising stomach acid but not food acid is completely wrong, bicarbonate secreted into the duodenum is going to lower overall pH of the digesta regardless of what's in there or where the acid came from (although the vast majority of it will be gastric acid anyway so it kind of doesn't matter). I can imagine this stuff having a differential effect if you mix it with your food before you eat it, then it can react with the food acid using up all it's buffering capacity because it gets to your stomach (so there is no alkaline left to react with HCl). But if you just take it orally then it's going to react with stomach acid just the same as food acid, and any claims from the manufacturers otherwise should be treated with caution.

Possibly worth keeping in mind that many many people artificially reduce their stomach acid to very low levels for very long periods of time with zero side effects (refluxy people like me taking proton pump inhibitors or H2ras, all of which has been well studied over long periods of time), so realistically if this stuff helps then it doesn't matter what it's doing to the HCl along the way. If it is just the reduction in acidity that works then anything else which reduces acid by straight chemical means, like tums, should have the same effect (although these have been shown to be very ineffective at actually reducing overall stomach acidity) and I don't see why a small amount of calcium glycerophosphate would magically be better. But the actual mechanism for why this stuff may help intestinal cystitis isn't known, and I'd want to see some independent studies done before I even believe that claim.

Actually that last point is probably the most important. Look for independent studies and see what they say about the mechanism. Chemical reactions in food like this should be pretty easy to study and if the health effects are real they can be picked up too, although the downstream effects on biochemistry won't be so easy. When a manufacturer says something like "protective stomach acid" red flags go up because it shows a real lack of understanding of basic digestive physiology.
posted by shelleycat at 2:10 PM on January 22, 2010

buffering capacity because it gets to your stomach

That should be *before* it gets to the stomach.
posted by shelleycat at 2:13 PM on January 22, 2010

Stomach acid isn't "protective" in any way.

In fact, stomach acid is protective against traveler's diarrhea and possibly also dangerous C. difficile infections; the rate of the latter has gone up greatly since stomach acid reducers have become so popular.

Stomach acid also helps to protect against deficiencies in vitamin B12; decreased stomach acidity is one of the causes of inadequate absorption of dietary B12.
posted by Ery at 2:36 PM on January 22, 2010

Right, the stomach acid has a job to do, and one of them is to try to kill pathogens that get into the tract. Thus, protective.

I remember reading somewhere that excessive use of acid reducers resulting in a permanent lower-acid condition in the stomach ends up ruining the stomach lining in some way.

My point about the different chemicals working in different ways was perhaps unclear. I was theorizing that this stuff neutralized the other acids in some other way than by a regular acid/base reaction. Instead of neutralizing the acid ions, it (for example) forms a precipitate with acetic acid, but not HCl.
posted by gjc at 3:31 PM on January 22, 2010

It does work; if I take two tablets before eating spaghetti with tomato sauce, it doesn't bother me a bit, although otherwise it's a problem.

Sounds like you haven't considered the placebo effect.
posted by gramcracker at 3:46 PM on January 22, 2010

That's a pretty big stretch though, plenty of infections are present even with full acid (and none of what you linked is peer reviewed). Here's one that is peer reviewed that discusses B12 status (keep in mind there are quack medicine claims that low stomach acid causes all kinds of problems and ready to sell you supplements to fix it, you really need to stick to the literature for this one).

Using that as justification for calling it 'protective' is weak, particularly given the negative effects stomach acid can have, the lack of ongoing side effects when it's reduced (as I said before this has been studied extensively), and the actual real protective mechanisms in place (e.g the mucous lining). That phrase sounds very much like marketing speak to this digestive physiologist and is still a huge red flag. Their other claims are also somewhat vague and the science is off.

So again, look for independent, peer reviewed information and go from there. The claims about interstitial cystitis are interesting and quite likely have merit, particularly as something about the calcium and/or phosphate itself may be what helps the problem rather than anything to do with acid. But without a solid mechanism or some real evidence it's pretty difficult to discuss.
posted by shelleycat at 3:48 PM on January 22, 2010

I remember reading somewhere that excessive use of acid reducers resulting in a permanent lower-acid condition in the stomach ends up ruining the stomach lining in some way.

This was thought to be the case for quite a while but has since been disproved. Repeatedly. Also note that PPIs aren't side effect free on their own, I can't tolerate them at all personally for example, but that's a separate issue from low stomach acidity. Which this stuff isn't going to do anyway any more than tums or the like, the feedback mechanisms in the stomach are too good for that. (also PPIs and H2ras work by blocking the enzymes that create HCl rather than interact with the HCl itself, so they're doing something very different than prerelief of calcium carbonate)
posted by shelleycat at 3:55 PM on January 22, 2010

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