Soy boy is a pejorative term sometimes used in online communities to describe men lacking masculine characteristics. The term bears many similarities and has been compared to the slang terms cuck (derived from cuckold), nu-male and low-T ("low
testosterone") – terms sometimes used as an insult for "male femininity" by online communities.
The term is based on the presence of the phytoestrogen isoflavone in soybeans, which has led some to claim that soy products feminize men who consume them, although there is no correlation between consumption of soy phytoestrogens and testosterone or estrogen levels or sperm quality.
The term is often used as an epithet by "
internet trolls". It is often targeted at perceived
social justice warriors, vegans, liberals, and similar groups. The term has also been used in online debates about the fashion appeal of cargo shorts.