Ok so I think I might have a possible theory for this.
My skin started breaking out more since I became a vegetarian. I've used many different acne products (including ProActiv) with no real success.
In my search for more acne solutions online, I came across a acne solution called "Pantothen". This product has two active ingredients called Pantothenic Acid and L-Carnitine. The company argues that a dietary deficiency may cause acne "based on the research of Dr. Lit-Hung Leung, who published his first study on the relationship between Pantothenic Acid and acne treatment in 1997".
Pantothenic Acid is more commonly known as Vitamin B5. So basically this "Pathothen" product is just an expensive, well marketed vitamin pill which I would not bother buying.
HOWEVER they may be onto something because both Pantothenic Acid and L-Carnitine are found in their highest concentrations in meat and dairy products. So vegans and vegetarians may be missing out on these nutrients that help prevent acne.
So what vegetarian/vegan food source contains these nutrients? Turns out that AVOCADOS have a fairly high concentration of both, so I'm going to try including a lot more in my diet and see how it goes. Of course there are lots of other vegetables that have these nutrients so for more information check out these wikipedia pages:
http://en.wikipedia.org/wiki/Pantothenic_acid#Dietary
http://en.wikipedia.org/wiki/Carnitine#Food