Having valid and reliable resting energy expenditure (REE) estimations is crucial toestablish reachable goals for dietary and exercise interventions. However, most of the REE predictiveequations were developed some time ago and, as the body composition of the current populationhas changed, it is highly relevant to assess the validity of REE predictive equations in contemporaryyoung adults. In addition, little is known about the role of sex and weight status on the validity ofthese predictive equations. Therefore, this study aimed to investigate the role of sex and weight statusin congruent validity of REE predictive equations in young adults. A total of 132 young healthy adults(67.4% women, 18–26 years old) participated in the study. We measured REE by indirect calorimetrystrictly following the standard procedures, and we compared it to 45 predictive equations. The mostaccurate equations were the following: (i) the Schofield and the “Food and Agriculture Organizationof the United Nations/World Health Organization/United Nations” (FAO/WHO/UNU) equationsin normal weight men; (ii) the Mifflin and FAO/WHO/UNU equations in normal weight women;(iii) the Livingston and Korth equations in overweight men; (iv) the Johnstone and Frankenfieldequations in overweight women; (v) the Owen and Bernstein equations in obese men; and (vi) theOwen equation in obese women. In conclusion, the results of this study show that the best equationto estimate REE depends on sex and weight status in young healthy adults.