Background/Objectives: Testosterone and cortisol are key regulators of metabolic, psychological, and physiological responses to environmental and lifestyle factors. This study aimed to analyze the relationship between free testosterone and cortisol concentrations and dietary patterns, stress levels, sleep quality, physical activity, and body composition in healthy young men (aged 18–35 years). Methods: This study included 40 volunteers who met our inclusion criteria. They underwent anthropometric measurements, body composition analysis, and biochemical determination of serum free testosterone and cortisol concentrations. Additionally, participants completed a set of validated questionnaires: a questionnaire regarding the frequency of consumption of specific foods and stimulants, a 3-day food diary, the PSS-10, the Holmes and Rahe Scale, the PSQI, and the Baecke Physical Activity Questionnaire. Results: Free testosterone concentration in blood was negatively correlated with body fat content and positively correlated with the percentage of energy, protein, fat, sodium, and folic acid requirements. Morning blood cortisol levels negatively correlated with body weight and height. Higher intakes of cholesterol, folic acid, and vitamin A resulted in statistically significant reductions in cortisol levels. A significant correlation was identified between poor sleep quality and low cortisol levels, particularly among men aged < 26 years. A positive correlation was also found between leisure-time physical activity and testosterone levels, particularly in the older group. Furthermore, a higher body weight and greater muscle mass were correlated with lower cortisol levels. Conclusions: These results provide a starting point for further research on neuroendocrine mechanisms in active individuals exposed to environmental stress.