Body Mass Index and Dietary Self-Regulation Are Associated with Attenuated Error Monitoring in Young Adults

Background/Objectives: Obesity is associated with alterations in cognitive control processes that support performance monitoring and dietary self-regulation, but the neurocognitive markers most closely tied to body weight status in young adulthood remain unclear. Methods: Sixty-two young adults completed a modified Simon task while continuous electroencephalography (EEG) was recorded. Response-locked event-related potentials (ERPs) were quantified for error-related negativity (ERN) and error positivity (Pe). The association between body mass index (BMI) and ERP amplitudes was examined under three parameterizations: BMI as a continuous variable, BMI split into three categories (normal weight, overweight, obese), and BMI split into two median-matched categories. Results: Higher BMI was associated with reduced (less negative) ERN amplitude under continuous (r = 0.30, p = 0.016, and median-split, Cohen’s d = −0.69, p = 0.009) specifications, and at the level of a trend under the three-group classification F(2, 59) = 2.80, p = 0.069, η2p = 0.09. The association was most consistent for neutral trials, where it reached significance under the continuous (r = 0.32, p = 0.010) and three-group (F = 3.31, p = 0.043) specifications and approached significance under the median-split (d = −0.51, p = 0.051). The BMI-ERN association remained significant after adjustment for age, sex, cardiorespiratory fitness, physical activity, and trait impulsivity. In contrast, Pe amplitude did not differ as a function of BMI under any specification. In exploratory analyses that did not survive correction for multiple comparisons, Pe amplitude was positively associated with mindful eating disinhibition and negatively associated with UPPS-P Positive Urgency, independent of BMI. Conclusions: These cross-sectional findings indicate that elevated adiposity in young adulthood is associated with attenuated pre-conscious conflict and error monitoring (i.e., ERN), whereas conscious error awareness (i.e., Pe) is unrelated to body weight status. The exploratory Pe–trait associations are offered as hypotheses for future confirmatory work rather than as established effects.