Research with deuterium-depleted water (DDW) in the last two decades proved that deuterium/hydrogen ratio has a key role in cell cycle regulation and cellular metabolism. The present study aimed to investigate the possible effect of deuterium-depleted organic compounds (DDOC) alone and in combination with DDW on cancer growth in two in vivo mouse models. To produce DDOC, drinking water of laying hens was replaced with DDW (25 ppm) for 6 weeks, resulting in 60 ppm D level in dried egg yolk that was used as deuterium-depleted food additive. In one model, 4T1, a cell line with high metastatic capacity to the lung, was inoculated in the mice’s mammary pad. After three weeks of treatment with DDW and/or DDOC, the tumor volume in the lungs was smaller in all treated groups vs. controls with natural D level. Tumor growth and survival in mice transplanted with MCF-7 breast cancer cell line showed that the anticancer effect of DDW was enhanced by food containing the deuterium-depleted yolk. The study confirmed the importance of D/H ratio not only in consumed water but also in metabolic water produced by the mitochondria while oxidizing nutrient molecules. This is in line with the concept that initiation of cell growth requires the cells to generate a higher D/H ratio, but DDW, DDOC, or the naturally low-D lipids in a ketogenic diet, have significant effect on tumor growth by preventing the cells from raising D/H ratio to the threshold.