It’s really just weird Christians convinced that if you eat enough bran flakes you won’t think about sex, updated for the 21st century.
It wasn’t just bran flakes - his whole schtick was about living life in as unstimulating a fashion as possible. Food that isn’t as dull and bland as possible might inflame the passions, and passion for something that doesn’t taste like cardboard might translate into passion of another kind. His original flakes were unsweetened, as were his contemporary Graham’s crackers in order to be as tasteless as possible.
Routine infant circumcision is a thing in the US because of the corn flakes nutter, the idea was that circumcision would reduce masturbation by cutting off a bunch of erogenous tissue without actually limiting your ability to reproduce. He also had a procedure for girls that involved burning the clitoris with acid to reduce sensitivity, but that one never took off to mass appeal and is illegal in every state now.