By definition, fasting is the abstention from eating and sometimes drinking, therefore in the ideal fasting scenario one should consume water only. However, fasting can be modified in accordance with your goals to obtain better results. If your goal is losing weight many supplements including NMN won’t change your insulin profile thereby having no negative effects on your fat loss. If your fasting goal is to increase NAD+ levels to improve mitochondria health and metabolic function, having NMN when you are fasting will likely increase even further. But if your goal is detoxification, water fasting is your regimen!