Back in the dark ages of the early 60's when I was a kid; I learned that chewing gum was made from the sap of a certain type of tree, and that this sap was called chicle. (Hence the name of "Chiclets" for one of the brands of chewing gum.)
But it turns out that perhaps by the mid 1940's, and certainly by the early 1950's, world demand far outstripped supply. So a new artificial substitute had to be found. Well they found one. Plastic. YES, plastic, with some petroleum based long chain polymers added.
Then it's dyed and coated with artificial colours and sweeteners.
So all of my life, while I have naively thought I was chewing chicle with flavours and sweeteners added, I was actually chewing a form of plastic.
Let's just say that I spent 15 years of my life working in a plastic factory, and would never have dreamed of putting that stuff in my mouth, no matter how pretty the colour was.

-And incidently, I wonder how old that documentary about chewing gum actually was that I saw on TV when I was a kid? Clearly it was already outdated information and no longer true, for it was 1958 or 1959 before my parents were able to buy our first TV set, and by then the artificial stuff was in use. I'm pretty sure I was 9 or 10 at the time I watched that outdated film about chewing gum, so the darn thing was upwards of 30 years old, as this would have been 1962 or 63 when I saw it on TV.
But it turns out that chicle is still being produced. So if you want to "go green" and chew the real thing instead of a hunk of plastic, you can.
Below are the links for the Chicza chewing gum company's American and Canadian websites. Don't worry European members. I saw in the program that the Chicza company also ships to the UK. So you should be able to buy the real thing over there if you want it. I did a quick Google and found a few places in the UK that sell the product.

The Chicza company claims to be operating sustainably, so that's good news too. Please use the American website for more information.
(The Canadian website is mostly just about ordering product, since they are a small company that has obtained the distribution rights here.)
USA: http://www.chiczausa.com/
Canada http://www.chiczagum.ca/home/