Abstract Background The benefits of providing optimal nutrition for recovery from illness and chronic health management are well documented. The measure of energy expenditure by indirect calorimetry or by predictive equations are two methods to assess energy needs. This abstract provides an overview of indirect calorimetry use in the outpatient setting. The study aims is to compare the results obtained with indirect calorimetry, with those obtained through the theoretical calculation with the Harris-Benedickt formula, by using t-student test. Methods This observational study was conducted from January 2019 to February 2020. The selected population is made up equally of men and women in the general population, from 18 to 65 years of age, without a specific disease, after having given informed consent. Our study was conducted in outpatient setting by using the fitmate pro to do the indirect calorimetry. Results A total of 50 patients were evaluated. The t-student test was used to evaluate whether there was a statistically significant difference in the population analyzed between the basal metabolic rate calculated with the Harris-Benedickt formula and the one measured by indirect calorimetry. The variables evaluated were gender, age (greater than or less than 38 years) BMI (greater than or less than 25). Conclusions A statistically significant results were found (with t-student less than 0.05) for patients over the age of 38 (0.006) and women (0.044). Not statistically significant results were found for the variables: male (0.64), under 38 years of age (0.98), BMI (0.15). Our study shows there are data in favor of the use of indirect calorimetry as a better method for assessing basal metabolic rate instead of Harris-Benedickt for a more targeted approach to the patient. Further studies may support results obtained in this study; furthermore, direct research is necessary in order to increase a personalized approach of the doctor towards the patient. Key messages Our study shows that there are data in favor of the use of indirect calorimetry as a patient-oriented approach to assessing basal metabolic rate. The study aims is to compare the results obtained with indirect calorimetry with those obtained through the theoretical calculation with the Harris-Benedickt formula.