I'll ignore the blatant sexism.
As a young woman, although admittedly not single, who happens to be vegan I really don't understand the point you are trying to make here.
I am vegan because I would rather not have had a sentient animal purposely killed for my meal - and it is a decision I came to after years of thought and consideration.
And yes, there is a growing trend of people caring what they put in their bodies - whether it is noticing that caffeine after 2pm disturbs their sleep, or that as they age they need to consider an increase in b12 or vitamin D - the majority of these choices are very rational ones - I have yet to meet a person whose diet choices fall out of the range of rationality - except, perhaps, the excuses people give me for not cutting down the amount of <insert foot they acknowledge they eat too much of> in their diet.