Why on earth they would call it this is beyond me considering the movie and all.... (look up soylent green if you haven't seen the movie.)
http://motherboard.vice.com/blog/drink-soylent-and-youll-never-have-to-eat-again
https://campaign.soylent.me/soylent-free-your-body
Everything the body needs – that we know of, anyway – vitamins, minerals and macronutrients like essential amino acids, carbohydrates and fat. For the fat, I just use olive oil and add fish oil. The carbs are an oligosaccharide, which is like sugar, but the molecules are longer, meaning it takes longer to metabolize and gives you a steady flow of energy for a longer period of time, rather than a sugar rush from something like fructose or table sugar. I also add some non-essentials like antioxidants and probiotics and lately have been experimenting with nootropics
I haven't seen the movie, but it is simply a geeky joke on a couple of levels -- the original soylent in the book was just soy and lentils (it was a story about poverty), but then they added cannibalism and made it the main theme of the movie for dramatic purposes. Since this product was originally just a blog post about someone's homemade liquid, naming it that was probably actually a smart marketing move that helped it go viral.
Nowadays thanks to Rob's blog posts, "soylent" has become a kind of generic term for liquid diet that is supposed to meet all your nutritional needs. Rob is making his own and selling it via CrowdFunder. But there are also "open source" versions for DIYers... like this one that I just started making for myself: http://www.cookingfor20.com/2013/06/18/hacker-school-soylent-recipe/
Unlike Rob's, this one is really based on soy. I'm considering scaling up and selling it for BTC... it actually tastes really good.