No differences were detected in energy intake or output between Klf3+/+ and Klf3−/− mice. A: Food intake was measured daily over 3 days in male 12-week Klf3+/+ (n = 7–9) and Klf3−/− (n = 5–6) mice fed either chow or high-fat diet. B: Energy in feces was determined by bomb calorimetry and data corrected for daily fecal output. Klf3+/+, n = 10; Klf3−/−, n = 7–8. C and D: Total energy expenditure determined from Vo2 and expressed as kJ/day per mouse and per gram of lean body mass (n = 7–10 per group). Data are means ± SEM. **P < 0.01, ***P < 0.001, chow vs. high-fat diet by ANCOVA. E and F: Relationship between individual energy expenditure data calculated as heat production and lean body mass; diet, but not genotype, significantly affects energy expenditure.