May be we have to look at this using the low of diminishing returns. At some point optimising your "healthy life-style" won't yield significant reduction in probability of getting sick. But on the other hand very unhealthy life-style will yield sickness with very high probability. I guess a good balance would be to allow yourself a "treat" from time to time, but generally avoid things which are well-known to cause health problems like smoking for example. Also remind yourself not to go over-board with the "healthy life-style".