"Soylent Green" was a bad Sci-Fi movie based very loosely on a 1966 novel, "Make Room! Make Room!" by Harry Harrison. The novel is a detective story set in a future that never happened: unrestrained population growth. It takes place in NYC, 1999, when the city's population is 40 million. Soylent Green is just one of several synthesized food products mentioned in passing in the book. Actual ingredients are soy and lentils.
You ought to be able to find the book in a decent sized library, or by interlibrary loan. Read it - it's a hell of a lot better than the movie.
Strelnikov