Leaving sex out of the equation was an unfortunate oversight. STDs cause a lot of grief and arguably as much or more damage than diet. AIDS speaks for itself; herpes is implicated in Alzheimer's, heart disease and other ailments and is just a general curse without the modern antivirals (although many persons are naturally immune); gonorrhea and syphilis continue to mutate to new drug-resistant forms.
On the other hand, sex has been found to have lots of benefits (I'm at work so I don't want to be looking up citations, but intuitively a few minutes of cardio can't be a bad thing).