Gluconeogenesis (GNG), the formation of glucose from non-carbohydrate precursors, requires adenosine triphosphate (ATP). Previous studies have estimated the energetic cost of GNG in humans based on theoretical calculations of rates of GNG, moles of oxygen consumption by GNG, and average oxygen consumption. Few human studies have measured the energy expenditure (EE) due to GNG. We estimated EE attributable to GNG in patients with three insulin resistance conditions and high GNG rates (insulin receptor pathogenic variants, lipodystrophy, and type 2 diabetes) and obesity without diabetes. Fractional GNG was measured by incorporation of deuterium from body water into newly formed glucose, endogenous glucose production (EGP) as glucose appearance following administration of [6,6-2H2] glucose, and total GNG as fractional GNG x EGP. EE was measured by indirect calorimetry and compared to predicted EE from the Mifflin St. Jeor equation. EE attributable to GNG was estimated using linear regression after accounting for age and FFM. EE in patients with insulin resistance was significantly higher than predicted by the Mifflin St. Jeor equation. GNG correlated with resting EE (REE). EE attributable to GNG in patients with insulin resistance was almost one-third of REE, substantially higher than theorized in healthy subjects. Our findings demonstrate that GNG is a significant contributor to EE in insulin resistant states. Prediction equations may underestimate caloric needs in patients with insulin resistance. Therefore, targeting caloric needs to account for higher EE due to increased GNG should be considered in energy balance studies in patients with insulin resistance.