There is controversy about the relationship between ACE I/D polymorphism and health. Seventy-four healthy adults (n = 28 women; 22.5 +/- 4.2 years) participated in this cross-sectional study aimed at determining the influence of ACE I/D polymorphism, ascertained by polymerase chain reaction, on cardiometabolic risk (i.e., waist circumference, body fat, blood pressure (BP), glucose, triglycerides, and inflammatory markers), maximal fat oxidation (MFO), cardiorespiratory fitness (maximal oxygen uptake), physical activity and diet. Our results showed differences by ACE I/D polymorphism in systolic BP (DD: 116.4 +/- 11.8 mmHg; ID: 116.7 +/- 6.3 mmHg; II: 109.4 +/- 12.3 mmHg, p = 0.035) and body fat (DD: 27.3 +/- 10.8%; ID: 22.6 +/- 9.7%; II: 19.3 +/- 7.1%, p = 0.030). Interestingly, a genotype*sex interaction in relativized MFO by lean mass (p = 0.048) was found. The DD polymorphism had higher MFO values than ID/II polymorphisms in men (8.4 +/- 3.0 vs. 6.5 +/- 2.9 mg/kg/min), while the ID/II polymorphisms showed higher R-MFO values than DD polymorphism in women (6.6 +/- 2.3 vs. 7.6 +/- 2.6 mg/kg/min). In conclusion, ACE I/D polymorphism is apparently associated with adiposity and BP, where a protective effect can be attributed to the II genotype, but not with cardiorespiratory fitness, diet and physical activity. Moreover, our study highlighted that there is a sexual dimorphism in the influence of ACE I/D gene polymorphism on MFO.