Why was the population so great in Soylent Green?

Soylent Green takes place in the 2040s and the population has become so great that they used up all the foodstuffs on Earth. Starvation is rampant so a company creates an edible product called Soylent Green

If all people are being fed a huge amount of the population must be killed, not just a few people, so if a large amount of people must disappear why is the population still so dense?