Adequate nutritional status is fundamental to cope with the disease and its treatments. The diagnosis of cancer does not necessitate a change in diet. In the case of unhealthy dietary habits, it is recommended to maintain a varied, balanced, and healthy diet that meets nutritional needs during this period. If you were following a vegan, macrobiotic, or vegetarian diet before the oncological diagnosis, you can continue doing so under dietary-nutritional supervision to ensure complete nutritional intake, but you should not make the change if it was not the case. Always consult with your designated medical team before following any diet that has not been prescribed within this team or hospital setting.