Hydrogen, due to its lightness, is very mobile among organic compounds, especially when its partner has higher electronegativity, like oxygen. You can think of hydrogen as the scrawny kid that gets pushed around by all the larger atoms, and oxygen as the bully that always takes his lunch money (the electron). Whenever the environment is energetic enough to ionize one hydrogen, the result is like the tea party in Alice in Wonderland. The hydrogens switch seats, and just end up drinking the same tea out of broken teacups.<p>The theory here is that if you make some hydrogens less scrawny (deuterium), the other atoms will preferentially pick on the lighter hydrogens, avoiding the destruction of the really important hydrogen-bearing molecules, like the fats in cell membranes.<p>Sounds good so far. But what happens when the fat needs to be recycled, or the deuterium swaps out to a different molecule?<p>Replacing 50% of a mammal's hydrogen with deuterium will cause the animal to die, from symptoms resembling radiation sickness, because spindle formation in mitosis relies upon Van der Waals forces, which are reduced in deuterium-containing molecules.<p>We aren't actually sure what else might go wrong in selectively deuterating the human body. So I think if I needed additional protection from oxidative damage, I'd try injecting my liver with L-gulonolactone oxidase before eating heavy fats. I may be wrong. We'll see.