Bioavailability of calcium carbonate


Continuing the discussion from (Soylent + Whey) and/or (other stuff) == Nausea? (1.5):

Calcium carbonate is a natural form of calcium. What would you suggest replacing it with?

Low bioavailability doesn’t matter if nutritional needs are met. Even if calcium carbonate has lower bioavailability than an alternative (e.g., calcium citrate), it also contains a high % of elemental calcium (40% in calcium carbonate vs. 21% in calcium citrate). It may be more efficient if you take that into account.

I found this interesting: Calcium bioavailability and absorption.

To cover an obligatory loss of 250 mg/day, the 800 mg/day RDA for adults assumes an average absorption of 30%.

I didn’t read the whole thing, but I skimmed it. Some tidbits:

  • Measuring the absorption accurately is a huge challenge.
  • Increased fiber intake can significantly reduce calcium absorption.
  • The body actually adapts to absorb calcium more efficiently when calcium-deficient, although this is not a reason to neglect calcium intake.
  • Calcitriol increases calcium absorption.

Soylent contains ergocalciferol (vitamin D2), which metabolizes to calcitriol. Exposing skin to sunlight should lead to increased calcium absorption as well; this is a great reason to visit a nude beach.


I should be more precise about it - organic form :smile:

I posted before about replacing all trace minerals in Soylent with amino acid chelated form, it’s relatively high bio-available and also released slowly and steadily into bloodstream.


I don’t know what you mean by “organic form” of calcium. I tried to google the term and I found a bunch of unscientific articles/advertisements selling organic calcium supplements. I hope that’s not what you meant.

I did a little more digging and apparently the “organic” calcium in at least one product is—wait for it—calcium carbonate!

As far as replacing all trace minerals with chelated forms, that doesn’t appear to be necessary at least, but I’m not aware of any potential benefits either. I googled this too and found more advertisements masquerading as scientific advice. I remain skeptical.

High bioavailability sounds good, but it doesn’t necessarily mean that form is better than another. A highly bioavailable form could be effectively worse than a low bioavailable form, or better in every way. More likely they would each have a mix of attributes in their favor. Bioavailability is only one aspect, and we can’t glean much useful information from one aspect in isolation.


“Organic” is a food term coined by the Devil himself.

It’s right up there with “chemical”.


Calcium carbonate neutralizes stomach acid. Good for some, bad for healthy people. Bioavailability decreases with age (particularly in women) so dosage must be increased - not ideal for aging gastrointestinal tracts and decreasing amounts of food / stomach acid.

There’s some good general information on calcium and supplements here


Your source, which I linked to as well and is specifically about supplemental forms of calcium rather than dietary calcium (Soylent is a food, not a supplement), conflicts somewhat with what you said:

Due to its dependence on stomach acid for absorption, calcium carbonate is absorbed most efficiently when taken with food, whereas calcium citrate is absorbed equally well when taken with or without food [4]. Calcium citrate is also useful for people with achlorhydria, inflammatory bowel disease, or absorption disorders [1].

Calcium citrate is useful as a supplemental form of calcium, or for people with various diseases, but I didn’t see any indication that calcium carbonate is not a perfectly acceptable form of calcium from food. Even as a supplement, it says:

As noted above, calcium carbonate is an acceptable form of supplemental calcium, especially for individuals who have normal levels of stomach acid.

From what I read (linked above), all calcium absorption decreases with age, especially in post-menopausal women.

There are better supplemental forms of calcium, especially for people with various diseases, but I haven’t yet seen any evidence that there is something deficient with calcium carbonate as a dietary source of calcium.


Calcium carbonate (caco3) as found in food or supplements is functional in the same way maltodextrin is a valid exclusive carb, dog food ingredients such as meat protein flour or chicken meal are valid sources of human nutrition as per chemical makeup and uptake - it’s not ideal but it’s abundant, cheap and effective (iirc caco3 makes up like 3% of the earths crust)

Caco3 is also the same as garden lime which is used to keep the pH value up for years eventhough slightly acidic rain and plants leach it out constantly. We humans want the same kind of calcium you can feed to plants without disrupting soil pH, which is chelated (metal suspended in liquid (yes calcium is metal))

Calcium and magnesium fight for uptake in the human body. That is, they need to be in balance or one will take over. If you have to do all sorts of calculations and adjustments based on your age, gender and overdo calcium (like if you supplement a caco3 soylent with a caco3 pill) you may end up with the calcium depositing in annoying places such as dental tartar, hard skin under feet or worse - blood clots.

I’ve seen a huge difference going to DIY with citrate instead of (EU-brand) with carbonate. My dental tartar and hard skin under feet have fallen off. I’m male 35. This is anecdotal I know. It may just as well be from a more bio-available magnesium source. Point is, if chelated, you know what you get. With calcium and magnesium, knowing exactly what you get/uptake is a real advantage.

Valid does not equal good, ideal, tasty, side-effect free or non-disgusting is all :smile: