Rapid Weight Loss in Competitive Boxers: Salivary Neuroendocrine and Neurotrophic Responses, Executive Function, and Eating Behavior Across Weight Cutting and Recovery

Background: Rapid weight loss (RWL) is widely practiced in boxing, yet its short-term associations with hydration, salivary biomarkers, executive function, and eating-related risk remain incompletely characterized. This prospective observational repeated-measures study examined competitive male boxers across baseline (T1), pre-weigh-in peak RWL (T2), and 12–18 h post-weigh-in recovery (T3). Methods: Sixty competitive male boxers were assessed using bioelectrical impedance analysis, urine-specific gravity, salivary osmolality, dietary intake, estimated energy availability (EA), salivary cortisol, testosterone, salivary alpha-amylase (sAA), spexin, apelin, brain-derived neurotrophic factor (BDNF), neuron-derived neurotrophic factor (NDNF), computerized executive-function/reaction-time tasks, and psychometric instruments assessing eating attitudes and affective state. Results: At T2, body mass decreased by 6.22 ± 1.48%, while estimated EA decreased from 42.8 ± 4.6 to 14.2 ± 3.8 kcal/kg fat-free mass/day (p < 0.001). Hydration indices worsened, cortisol and sAA increased, and salivary testosterone, spexin, apelin, BDNF, and NDNF decreased. Executive-task performance, reaction time, state anxiety, and mood disturbance also deteriorated. After 12–18 h recovery, several physiological, salivary, and cognitive outcomes remained different from baseline under the observed self-directed recovery conditions. Linear regression identified acute weight-loss magnitude, lower estimated EA, hydration stress, and salivary biomarker shifts as correlates of Stroop slowing; these models are exploratory and associative. Unmeasured salivary flow and assay quantification limitations constrain interpretation of the biomarker associations. In addition, 38.3% of participants exceeded the EAT-26 screening threshold for elevated eating-disorder risk. Conclusions: In this cohort, real-world RWL was temporally associated with dehydration, very low estimated EA, salivary stress-marker changes, slower executive-task performance, and elevated eating-risk screening. Given the absence of a non-weight-cutting control group and the concentration-based nature of peripheral salivary measurements, these findings should be interpreted as ecologically relevant observational associations requiring confirmation in controlled, larger cohorts.