Leveraging machine learning to identify gendered stereotypes and body image concerns on diet and fitness online forums.

The pervasive expectations about ideal body types in Western society can lead to body image concerns, dissatisfaction, and in extreme cases, eating disorders and other psychopathologies related to body image. While previous research has focused on online pro-anorexia communities glorifying the "thin ideal", less attention has been given to the broader spectrum of body image concerns or how emerging disorders like muscle dysmorphia ("bigorexia") present in online platforms. To address this gap, we analyze 46 Reddit forums related to diet, fitness, and mental health. We mapped these communities along gender and body ideal dimensions, revealing distinct patterns of emotional expression and community support. Feminine-oriented communities, especially those endorsing the thin ideal, expressed higher levels of negative emotions and received caring comments in response. In contrast, muscular ideal communities displayed less negativity, regardless of gender orientation, but received aggressive compliments in response, marked by admiration and toxicity. Mental health discussions aligned more with thin ideal, feminine-leaning spaces. By uncovering these gendered emotional dynamics, our findings can inform the development of moderation strategies that foster supportive interactions while reducing exposure to harmful content.