Gaucher disease type III (GD III) is a rare form of GD characterized by neurological involvement and severe systemic disease. The objective of this study was to assess the nutritional status and energy metabolism of patients with GD III. Methods: The basal metabolic rate (BMR, measured by indirect calorimetry) and anthropometric parameters (height, weight, body mass index (BMI), and arm circumference) of three patients with GD III (p.L444P/L444P genotype) were assessed at different time points. The clinical severity of GD was assessed by means of physical examination, laboratory tests, imaging findings, and the severity scores proposed by Zimran (SSI) and Davies (SSNI). Results: The measured BMR of patients 1 (age 14 years, not on enzyme replacement therapy (ERT), SSI score 33, SSNI score 14.5), 2 (age 17 years, on ERT, SSI score 33, SSNI score 16), and 3 (age 20 years, on ERT, SSI score 33, SSNI score 7.5) was, respectively, 47%, 72%, and 15% higher than that estimated by the Harris–Benedict equation. Patients with a more severe phenotype had more marked hypermetabolism. Patients 1 and 2 had BMI-for-age z scores of −1.09 and −1.39, respectively, and height-for-age z scores of −4.27 and −3.02, respectively; patient 3 had a BMI of 24.7 kg/m2. Conclusion: All three patients showed hypermetabolism; however, the two patients with the highest BMR had more severe GD and were malnourished. Additional studies are warranted to assess whether hypermetabolism may be a biomarker of disease severity in GD.