Soy boy

Soy boy is a pejorative term sometimes used in online communities to describe men perceived to be 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 insults 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 this is a discredited conspiracy theory with no scientific evidence for the correlation between consumption of soy phytoestrogens and testosterone or estrogen levels or sperm quality.

Biology
Soy products contain high amounts of phytoestrogens. As they are structurally similar to estradiol (the major female sex hormone) and have activity at the estrogen receptor, concerns have been raised that it may act as an endocrine disruptor that adversely affects health. The Harvard School of Health, however, notes that "there are many factors that make it difficult to construct blanket statements about the health effects of soy."

Usage
The term is often used as an epithet by internet trolls. It is often targeted at perceived social justice warriors, vegans, social liberals, and similar groups. The term has also been used in online debates about the fashion appeal of cargo shorts.

Soy boys are often depicted as feminized and unathletic, usually with glasses and a poorly groomed beard, and having a characteristic open-mouthed smile called a "soy face" or "soylent grin", a pun on the 1973 dystopian film Soylent Green.

Diet and men's health
While there is some evidence that phytoestrogens may affect male fertility, "further investigation is needed before a firm conclusion can be drawn". Several review studies have not found any effect of phytoestrogens on sperm quality or reproductive hormone levels.

Soy is rich in nutrients and likely to provide health benefits, especially when it replaces red or processed meat. Avoidance of red and processed meat was found to lower risk of developing erectile dysfunction. Higher soy intake is also associated with lower risk for prostate cancer.