If I understand correctly, the primary causality is with the energy substrates where fat is the most effective (of the main three - fat, protein, starch/carbs) with regard to endogenous DDW (deuterium-depleted water) production.
Then there's the question of DDW intake-outcome ratio that just doesn't make any sense at a glance. It's like a 10% difference in intake produces a 50% difference in plasma level. It doesn't make any sense if we assume that there's a direct mass-to-mass correlation. On the other hand, it doesn't make any sense either if we start with the premise that deuterium displaces hydrogen and then interferes with functions where some of these functions are involved in the management of deuterium, and then we assume that it's still just a question of mass-to-mass correlation. Just the fact that the observation doesn't match mass-to-mass expectations should tell us that there's more to it than just mass-to-mass.
It's hard to explain how I see it but imagine you're making shovels, and to make shovels you need tools that do exactly what shovels do (need shovels to make shovels, get it?), and the only such tools available are either shovels or very leaky sieves, and the only tools available now is those pesky sieves. So initially the work is very slow, but once you make your first shovel, work efficiency just goes through the roof and the next shovel you make is that much cheaper and quicker to make, and so forth. Now extend this to a huge matrix (like the body where there's something like trillions of such points) where each production point requires any number of other production points, and no production point can produce anything until it gets the output of the other production points. Now start with a matrix where all points have shovels, then introduce a very leaky sieve at just one point. Every point that relies on that sieve point produces anything only when this sieve point produces something, and this sieve point's output rate is very very low, so all points that rely on this one are obviously low as well. Now extend this to all the other points that rely on those shovel points that rely on that single sieve point and you can see how even a single point within the matrix can affect the entire matrix in such a hugely disproportionate ratio. Well, now do the same thing but introduce a shovel instead at a point where there used to be a leaky sieve, and that's what DDW does.
Now let's add transport into the mix, so we get output-input and input-output. So, output-input is between two points (that's the transport), and input-output is production time within a point. Now let's say that transport also needs shovels to move things along between two points. So even if two points that rely on each other both have shovels, if transport still uses only a sieve, those two points will only be as productive as what that sluggish transport can supply. Now let's add backup handling to the system, where if a point can produce more than another point can take in, a system kicks in and stops that initial point so its output doesn't clog transport. Now let's say that this backup handling system also needs a shovel, but it's only got a sieve. Now let's say that some points need multiple shovels and have a high chance to blow up even if just one of those shovels gets replaced with a sieve. Now let's say that the repair systems that go in and fix this break also need shovels, and so forth.
Does this make any sense?
Anyways, we're talking water here and fairly recently I watched a couple lectures by Gerald Pollack on what he calls EZ water (EZ stands for exclusion zone). I just did a quick search for DDW and found a site called Dancing with Water that deals with pretty much everything about water, its properties and its effects on various things. So on their page about DDW they got a lecture where the speaker briefly mentions Gerald and his work on water. Here's that lecture: https://www.youtube.com/watch?v=HAbKmyjvFaY
And here's Gerald's: https://www.youtube.com/watch?v=TPvYxDDpAgo
Now here's something that could be significant about Gerald's work in the context of deuterium and DDW. He discovered that water (H2O) separates into H+ and OH- when exposed to light. Well if light can separate one H from H2O, it can probably separate one deuterium from heavy water. And if it can do that, it would explain at least part of the biological mechanisms that handle excess deuterium. So for example when EZ water forms and expands, it excludes the separated H+ which could then be transported elsewhere. And because EZ water cycles between expansion and contraction, the process of separating and excluding H+ and transporting it elsewhere is repeated, and this would also be true for deuterium separation exclusion and transport.
Now the thing that puzzles me is that dietary fat is most effective at endogenous DDW production, and how. I imagine that it's got something to do with the hormones that regulate water, i.e. where it goes, how much is stored and where, etc, and how these hormones are differently affected by those main three energy substrates. I mean, it puzzles me but all I really need to know is which one is most effective.