It depends on the person. Statistical studies pertaining to nature vs. nurture like to vary a lot on how much genetics or nurture-type influences change outcomes.

One's genetic background is only a probability figure. One's nutrition and general health measures can and often does counteract one's genetic probability. My health measures are paramount to me.

Nutrition won't change the genetic background. Ionizing radiation may, in a fully unpredictable manner.
The science of nutrition is rapidly growing and changing. There are a lot of unknown areas.
Looks like, in general, genes won't determine a patient's lifespan and illnesses but rather make some outcomes more or less likely. Proper nutrition and lifestyle may decrease the probability of negative outcomes.