Exposure to radiation up-regulates
genes involved in DNA repair pathways,
genes associated with antioxidant
defense (notably those downstream of the Nrf2
transcription factor) and autophagy-related genes (which are crucial for the degradation and
recycling of cellular components).
Fasting does all those things, too -- without introducing random errors into one's DNA. Basically everyone under 40 should do regular fasts of some form, and those that do will probably derive no additional benefit from exposure to ionizing radiation, i.e., the type of radiation being promoted by the OP. (People older than 40 need to worry about losing muscle mass during a fast since old people find it very hard regain muscle mass once it it lost. Actually it is likely that only people over 60 or 65 might have to worry about muscle mass: experts disagree on the best cut-off age, and 40 years old's is the lowest I have seen.)
Three days of fasting has all of the benefits I list above, but there are risks to going completely without calories for that long, and actually our ancestors probably went without any access to calories for days almost never, but often endured stretches of days in which their calorie intake was less than a sustainable level, but not zero. To reduce the risks of going completely without calories for 3 days at a time, longevity researchers have devised the "fasting-mimicking diet", which give over the course of 5 days most or all of the benefits as eating no calories at all for 3 days. It restricts calories to about 800 calories per day with only 10% of that coming from protein and is the type of fasting that most people should be doing.
FMD requires no interaction with or prescription from the health-care industry and costs nothing except the time and attention needed to learn how to count calories if one has never done that before.