It is interesting that some people don't seem to "get" this ad. For those people: How many of you complain about beautiful women in ads for other things, such as cars or boats or whatever other thing in which the women are there just to get your attention? Isn't it hypocritical to complain about beautiful women with vegetables in ads, but not complain about beautiful women with cars in ads? It seems that something else must be bothering you.
In the case of the PETA ad, there is some relevance, as a healthy lifestyle (including a healthy diet) is good for one's ability to perform sexually. Clogging your blood vessels with cholesterol can lead to impotence, because blood flow is essential for an erection.