To synthesize water, you need electrons, protons and oxygen. The vast majority of hydrogen nuclei are made up of the single proton. But 0.015% (or one in 6,600) of these hydrogen nuclei are not made up of just one proton, but one proton and one neutron. Tis isotope is called deuterium. This deuterium had its heyday in the battle for heavy watter during World War II. In heavy water, the hydrogen nuclei are essentially deuterium. The weight of the atom has therefore doubled. This heavy water will slow the flow of neutrons in nuclear reactors and facilitate the production of plutonium, the fuel for the atomic bomb. This is the reason why the allies put all their efforts to slow down the production of heavy water by the Germans.

Deuterium is extracted from water for the needs of the nuclear industry. The result is deuterium-depleted water that can be used in biology and medicine. Water depleted in deuterium is therefore a consequence of the nuclear industry. This has long been the preserve of Eastern Europe and in particular the Hungarians. Depleting water in deuterium is to make the water lighter because the common hydrogen nucleus, unlike deuterium, does not include these heavy neutrons.
During cell digestion, the proton is torn from the glucose molecule, it is transported into the mitochondria where it will be excreted between the inner membrane and the outer membrane of this mitochondria. It will re-enter the mitochondria by rotating a pump called ATP synthase. This pump in turn will activate the synthesis of ATP. The proton once in the mitochondria will be combined with electrons and oxygen to synthesize water.
These precision mechanics will be destroyed when the mass of hydrogen is doubled by its isotope deuterium. The deuterium will destroy the ATP synthase and the synthesis of water will not take place. Water depleted in this heavy deuterium will restart mitochondrial activity. Entropy may escape as heat and cell growth will cease.

Olgun, A. (2007). Biological effects of deuteronation: ATP synthase as an example. Theoretical Biology and Medical Modeling, 4 (1), 1-4.

 

Water depleted in deuterium modulates and decreases the frequency of cancers induced by chemical molecules. For these Hungarian scientists, the ketogenic diet is beneficial because it is naturally low in deuterium.

Gyongyi, Zoltan, Gabor. Deuterium depletion can decrease the expression of C-myc, Ha-ras and p53 gene in carcinogen-treated mice. In vivo (Athens, Greece), 2000, vol. 14, no 3, p. 437-439.

Somlyai, G., Laskay, G., Berkényi, T., Galbács, Z., Galbács, G., Kiss, S. A., Jancsó, G. (1999). The biological effects of deuterium-depleted water, a possible new tool in cancer therapy. Zeitschrift fur Onkologie, 30, 91-94.

 

Normal water contains 150 ppm deuterium. There are several commercial forms at 125-, 105-, 85-, 65-, 45- and 25 ppm. It seems good to start with water at 85 ppm then to decrease regularly in stages of two months. Water low in deuterium is not without side effects because it stimulates the metabolism and in particular the brain and some patients have complained of insomnia. This means that this treatment cannot be done without medical supervision.
Thousands of cancer patients, mostly Hungarians, supplement their treatment with a drink depleted in deuterium. Most of these are not randomized studies but feedback. Hungarian doctors compare patients drinking depleted water to other patients treated without drinking water changes years before. They claim that low-deuterium water doubles cancer survival.

Kovács, A., Guller, I., Krempels, K., Somlyai, I., Jánosi, I., Gyomgyi, Z., Ember, I. G. S. (2011). Deuterium depletion may delay the progression of prostate cancer. Journal of Cancer Therapy, 2 (4), 548-556.

 

The combination of deuterium-depleted water with drugs such as methylene blue or chlorine dioxide has not been studied.
Like any treatment that stimulates mitochondrial activity, the effectiveness of deuterium-depleted water is not limited to cancer. Many athletes want to improve their performance. Scientists claim that this water is beneficial.

Györe I., Somlyai G. (2005) The effect of deuterium depleted drinking water on the performance of sportsmen. Hungarian Review of Sports Medicine 46/1: 27-38.

 

Likewise, a drink low in deuterium reduces pathological obesity by boosting mitochondrial combustion.

Halenova, T., Zlatskiy, I., Syroeshkin, A., Maximova, T., & Pleteneva, T. (2020). Deuterium-depleted water as adjuvant therapeutic agent for treatment of diet-induced obesity in rats. Molecules, 25 (1), 23.