Deuterium is an isotope of hydrogen.
Water found in nature contains both H2O (two atoms of hydrogen and one of oxygen) and D2O (two atoms of deuterium and one of oxygen).
D2O concentration is normally very low, for example, near 140 part per million (ppm) in drinking water. Heavy water contains a higher concentration of deuterium.
Based on the energy source (glucose or fat), metabolic water, i.e. the water stemming from the oxidative metabolism of the energy source of a cell, which combines hydrogen or deuterium atoms from the energy source and the oxygen from respiration, features relatively low or high D2O concentration. Indeed, carbohydrates (especially fruits), are relatively high in deuterium atoms while fat (especially polyunsaturated fats) are relatively low. That’s why some of the researchers advising for Deuterium Depleted Water also advises for the Ketogenic diet, which is carbohydrates restriction.
The research that has been carried out regarding deuterium shows that:
it has a role in the regulation of cell growth, low deuterium concentration impairs the division of cells, high deuterium concentration allows high division rate;
low deuterium conditions can make cancerous cells die while healthy cells can adapt;
the deuterium concentration of the water contained in cells can influence the functioning of some proteins that are involved in ATP (the “energy currency of the cells”) production. The rational is that too much deuterium can impair these proteins which are thought to function as “nanomotors” because deuterium atoms are far more heavy than hydrogen ones and they could thus break them.
Deuterium Depleted Water (DDW) is a costly product but it can be thought that limiting the water consumed could be helpful, in particular in the context of a low carbohydrate diet, which reduces the consumption of deuterium from food, in parallel of the reduction from limited water consumption.
Restricting water could also have effects that consuming DDW doesn’t have regarding cancer :
immune system stimulation (cf. osmotic stress effects),
osmolyte metabolism promotion,
reduction of cells edema, allowing the oxygen to reach the mitochondria (cancer cells have a greater water quantity than healthy cells, which is by the way exploited to diagnose cancer).
The following book is a good resource about the research on DDW and how to use it:
Deuterium Depletion - A New Way in Curing Cancer and Preserving Health