Body fat and muscularity dissatisfaction are not prospectively associated with psychological wellbeing among sexual minority men: A case for separating within- and between-person variation in examinations of body image phenomena and their outcomes.

Extensive cross-sectional research reports that body fat and muscularity dissatisfaction contribute to negative psychological outcomes among sexual minority men; however, longitudinal models are necessary for accurately quantifying the strength and direction of these relationships. We investigated the bidirectional longitudinal relationships of body fat and muscularity dissatisfaction with psychological quality of life among 2953 sexual minority men using random intercept cross-lagged panel models. Consistent with existing literature, we found that higher average muscularity and body fat dissatisfaction were associated with higher average psychological quality of life impairment between-persons. Unexpectedly, these constructs were not significantly associated within-persons/longitudinally. These findings conflict existing literature's conclusions that muscularity and body fat dissatisfaction consistently contribute to poorer psychological wellbeing in this population. A significant between-person relationship in the absence of within-person relationships suggests that intermediary constructs (e.g., body ideal internalization) may account for the between-person effects of muscularity and body fat dissatisfaction on psychological wellbeing. Future research can accurately estimate these effects and identify reliable intervention targets by ensuring that within- and between-person relationships are examined separately, rather than being conflated.