Cardiovascular disease is the leading cause of death in firefighters (FF) around the nation. Recent observational studies have emerged suggesting that FF consume calorically dense foods, high in sugar and fat, but low in nutritional value which can exacerbate heart diseases and impair performance. The potential to improve cardiometabolic and performance measurements when following a carbohydrate (CHO) restricted diet (CRD) has gained interest in the literature. To date, only one study has employed a nutrition intervention in FF, yet its’ focus was on nutrient dense foods and antioxidant supplements. Therefore, the purpose of this study was to examine the cardiometabolic and performance effects of a 28-day CRD in FF. 15 career FF participated and finished the present study. Participants reported to the laboratory on 9 separate occasions. Trial 1 consisted of participants having a blood draw performed for assessment of their heart disease risk followed by body composition, blood pressure, and a glucose challenge test (GCT) to assess glucose impairment following ingestion of a 75 g glucose beverage. Trial 2 consisted of a graded exercise cycling test with 5 stages followed by a maximal Wingate for 30 s. Finally, the last trial included the FF physical performance assessment (FPPA) which consisted of a 2.41-km run followed by 2 min of maximal pull-ups, push-ups, and sit-ups. The first 3 trials were used as familiarizations, the second 3 trials were used as baseline measurements, and the last 3 trials followed the 28-day CRD. The CRD consisted of ad-libitum consumption of fat and protein and keeping CHO < 25% daily kilocalorie intake. Dependent variables measured pre- and post-diet included body composition, lipid profile, insulin, cortisol, c-reactive protein (CRP), GCT, substrate oxidation rates, Wingate variables, and the FPPA. Following the diet, participants had significant reductions in CRP, blood pressure, 2.41-km run time, CHO oxidation rates, and fat mass. Participants also had significant increases in high density cholesterol count, fat oxidation rates, and pull-up repetitions. Overall, our results show that a CRD in a high-stress occupation can favorably change markers of heart disease and body composition without decrements to physical performance.