Background/Objectives: While body dissatisfaction is frequently studied as an outcome of physical activity, less is known about how pre-existing body image perceptions shape the quality of behavioral regulation. Grounded in Self-Determination Theory, this study aimed to investigate the associations of different perceived body image discrepancy profiles with autonomous and controlled motivation for both exercise and eating, and to explore the interaction effects between these profiles and sex. Methods: The sample comprised 939 regular gym exercisers (32.99 ± 11.90 years; 55.1% female). Using the Stunkard Figure Rating Scale, participants were categorized into four discrepancy profiles: desire to increase, satisfied, mild desire to reduce, and moderate/severe desire to reduce. Data were analyzed using Two-Way ANOVAs. Results: The Satisfied group reported the highest autonomous and lowest controlled motivation across both domains (main effects: p < 0.001, η²_p = 0.019–0.046). A significant body image × sex interaction emerged for controlled eating motivation (F(3, 931) = 6.22, p < 0.001, η²_p = 0.020). Females exhibited a “U-shaped” curve, demonstrating low controlled eating motivation when satisfied (M = 1.65) but elevated levels at extremes (desire to increase: M = 2.50; moderate/severe desire to reduce: M = 2.39). Males maintained stable controlled eating motivation across all discrepancy profiles (M = 2.06–2.30). Although these main and interaction effects were statistically significant, all observed multivariate effect sizes were small (η²_p = 0.012–0.046). Conclusions: Perceived body image discrepancy acts as a significant antecedent of motivational quality. The absence of a perceptual gap is linked to highly adaptive, autonomous behavioral regulation. Furthermore, the distinct sex-based patterns in controlled eating motivation underscore the necessity for health and exercise professionals to adopt tailored, sex-specific strategies when addressing body image concerns.