Hi Jean-Louis,

Nice to hear from you again (despite our friendly differences).

> rennin is indeed a proteolytic enzyme that digests casein and
> coagulates milk.

Rennin certainly coagulates milk but does not "digest" casein..it
merely releases the calcium bonded to casein.

> The effect is a longer retaining in the stomach, and
> enhanced digestion (since enzymes have more time to act).

You call a longer retention in the stomach "enhanced digestion"??

> But even in
> the absence of rennin, casein can still be digested by other
> proteolytic enzymes (pepsin and trypsin). I am not saying that
> digestion is 100% efficient, but that rennin is not absolutely
> necessary.

Rennin is necessary in order to get at the calcium which is
bonded to the casein...nothing more and nothing less apart
from the coagulation.

> In the article I cited, it was said that 25% of the calcium
> in milk is absorbed (figure obtained by radioisotope labeling), so
> calcium in milk is indeed bioavailable (but milk might increase bone
> loss for other reasons).
>
Even if this were true, it would merely demonstrate that milk is
a relatively poor source of calcium. And if you take (your previous
figures) the ratio of phosphorus to calcium then it is more than
apparent that milk MUST rob the bones of calcium in order to
balance out the imbalance.

> In the past, rennin (extracted from calves' stomachs) was used to make
> cheese. Now, manufacturers use other enzymes that have the same effect
> on casein. Thus, pre-digested forms of milk (like cheese) are more
> digestible than milk itself.

Have you ever wondered why rennin is not (can not be) extracted from
either cows' stomachs or even human stomachs? Both calves and human
babies produce it...for obvious reasons..the adults of both species
do not (as with Africans, for example, or certainly not nearly enough).

Best regards,

Alan